Cosmetic/dermatological compositions, well suited, e.g., for skin-firming and anti-aging applications, as well as for stimulating the proliferation of dermal fibroblasts, comprise effective skin affliction-alleviating amounts of (a) at least one hydroxystilbene compound, in immixture with (b) at least one ascorbic acid compound, advantageously formulated into a topically applicable, physiologically/cosmetically acceptable vehicle, diluent or carrier therefor.

This application claims priority under 35 U.S.C. xc2xa7119 of FR-99/08570, filed Jul. 2, 1999, hereby expressly incorporated by reference.
1. Technical Field of the Invention
The present invention relates to novel cosmetic/dermatological compositions comprising at least one hydroxystilbene in intimate admixture with ascorbic acid, especially for skin-firming applications.
In particular, the novel compositions of this invention are well suited to stimulate the restructuring of the skin and/or mucous membranes by stimulating the proliferation of the dermal fibroblasts.
2. Description of the Prior Art
Human skin includes two compartments or constituents, i.e., a superficial compartment, the epidermis, and a deep compartment, the dermis.
Natural human skin is principally composed of three types of cell: the keratinocytes, which are the vast majority, the melanocytes and the Langerhans cells. Each of these cell types contributes, by virtue of its intrinsic functions, towards the essential role played in the body by the skin.
The dermis provides the epidermis with a soft support. It is also the epidermis"" nourishing factor. It primarily includes fibroblasts and an extracellular matrix itself composed of different extracellular proteins, among which are, in particular, collagen, elastin and various glycoproteins. This assembly of extracellular components is synthesized by the fibroblasts. Leukocytes, mastocytes and tissue macrophages are also found in the dermis. Too, the dermis contains blood vessels and nerve fibers.
On account of their activity in the synthesis of the extracellular matrix proteins (proteoglycans, collagen fibers and other structural glycoproteins), the fibroblasts are the principal factors involved in the structural development of the dermis.
The collagen fibers provide the dermis with solidity. They are very strong, but are sensitive to certain enzymes generally referred to as collagenases. In the dermis, the collagen fibers comprise fibrils sealed together, thus forming more than ten different types of structure. The structure of the dermis is essentially due to the overlapping of the trapped collagen fibers. The collagen fibers contribute to the skin""s tonicity. The collagen fibers are regularly renewed, but this renewal decreases with age, thus leading, especially, to a thinning of the dermis. This thinning of the dermis is also due to pathological causes such as, for example, the hypersecretion of corticoid hormones, certain diseases (Marfan""s syndrome, Ehlers-Danlos syndrome) or vitamin deficiencies (scurvy). It is also accepted that extrinsic factors such as ultraviolet radiation, tobacco or certain treatments (retinoic acid and derivatives, glucocorticoids, vitamin D and derivatives, for example) also have an effect on the skin and on its collagen level.
Degradation of the collagen fibers results, notably, in the appearance of loose, wrinkled skin which individuals have always tried to combat, since skin which looks smooth and taut is obviously more preferred.
Moreover, during menopause, the principal changes relating to the dermis are a decrease in the level of collagen and in the thickness of the dermis. In menopausal women, this results in thinning of the skin. Women thus experience a sensation of xe2x80x9cdry skinxe2x80x9d or of skin which feels tight, and an increase in the level of surface wrinkles and fine lines developed. The skin feels rough to the touch. Lastly, the skin is less supple. It is demonstrated that women gradually lose their level of collagen yearly after menopause and that 30% of the overall level is lost in the first five years after menopause.
Thus, serious need continues to exist for alternative active agents that maintain the level of collagen in the skin and also maintain the smooth and taut appearance of the skin.
One approach for achieving this result entails stimulating the proliferation of the fibroblasts and, consequently, on account of the increase in the number of secretory cells in the dermis, also maintaining or even reinforcing/enhancing the synthesis of collagen.
It has now surprisingly and unexpectedly been determined that association of at least one hydroxystilbene with ascorbic acid or one of the analogs thereof presents the attribute of stimulating the proliferation of the dermal fibroblasts in proportions that are higher than those which would reasonably be expected by simple addition of the effects of each of these components taken separately.
More particularly according to the present invention, the subject hydroxystilbenes are compounds having the following structural formula (I):
in which n is an integer ranging from 0 to 4, inclusive, and m is an integer ranging from 0 to 5, inclusive.
These compounds can be in cis- or trans-configuration.
According to this invention, by the term xe2x80x9chydroxystilbenexe2x80x9d are intended both the compounds of formula I and the hydroxyalkyl derivatives thereof.
The hydroxystilbenes are compounds that exist in the natural state in plants of the Spermatophyte class and particularly in vine. Such compounds as, for example, resveratrol are found in grapes and in wine.
In the prior art, the hydroxystilbenes are useful, inter alia, as depigmenting agents (JP-87/192,040), as vasodilators (EP-96/830,517), as antithrombin agents (JP-05/016,413), for the treatment of various cardiovascular conditions (CA-2,187,990), as mutagenesis and carcinogenesis inhibitors (JP-06/024,967) or are described as antioxidants.
Among these compounds, resveratrol (or 3,5,4xe2x80x2-trihydroxystilbene) is particularly interesting for the activities described above, notably because it is a natural compound which is found in the skin of grapeseeds and in wine. In this regard, the review by Soleas et al. (Clinical Biochemistry, Vol. 30, No. 2, pp. 91-113 (1997)) well summarizes the state of the art regarding this compound and hydroxystilbenes.
Moreover, ascorbic acid (or vitamin C) is known to stimulate collagen synthesis by preventing, as a co-factor, the self-inactivation of the lysine and proline hydroxylase enzymes and by increasing the synthesis of procollagen mRNAs. Ascorbic acid (or vitamin C) is also known to stimulate the synthesis of elastin in the skin. In this regard, compare U.S. Pat. Nos. 5,801,192 and 4,983,382 and EP-0,717,983. See, also the article entitled xe2x80x9cPola to incorporate vitamin C in new cosmetics line for skin carexe2x80x9d from the Japan Economic Journal of Jun. 5, 1984 (page 15). Thus, it has been described that ascorbic acid in cosmetic compositions is useful for treating wrinkles (Fragrance Journal, Vol. 8, No. 6(45) (1980) pp. 38-43, xe2x80x9cCosmetic and vitamin action and safety to dermatologyxe2x80x9d).
Thus, the present invention features compositions comprising, in a physiologically acceptable medium, at least one hydroxystilbene in immixture with ascorbic acid or with an analog thereof.
The subject compositions are particularly suited for stimulating the proliferation of dermal fibroblasts.
Exemplary hydroxystilbenes according to this invention are mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa- and nonahydroxystilbenes, or, alternatively, hydroxyalkyl derivatives thereof.
According to the invention, the hydroxystilbenes can be used alone or as mixtures of any nature and can be of natural or synthetic origin.
The hydroxystilbenes according to the invention are preferably selected from among:
4xe2x80x2-hydroxystilbene,
2xe2x80x2,4xe2x80x2-dihydroxystilbene,
3xe2x80x2,4xe2x80x2-dihydroxystilbene,
4,4xe2x80x2-dihydroxystilbene,
2xe2x80x2,4xe2x80x2,4-trihydroxystilbene,
3xe2x80x2,4xe2x80x2,4-trihydroxystilbene,
2,4,4xe2x80x2-trihydroxystilbene,
3,4,4xe2x80x2-trihydroxystilbene,
3,4xe2x80x2,5-trihydroxystilbene,
2xe2x80x2,3,4-trihydroxystilbene,
2,3xe2x80x2,4-trihydroxystilbene,
2xe2x80x2,2,4xe2x80x2-trihydroxystilbene,
2,4,4xe2x80x2,5-tetrahydroxystilbene,
2xe2x80x2,3,4xe2x80x2,5-tetrahydroxystilbene,
2,2xe2x80x2,4,4xe2x80x2-tetrahydroxystilbene,
3,3xe2x80x2,4xe2x80x2,5-tetrahydroxystilbene,
2,3xe2x80x2,4,4xe2x80x2-tetrahydroxystilbene,
3,3xe2x80x2,4,4xe2x80x2-tetrahydroxystilbene,
3,3xe2x80x2,4xe2x80x2,5,5xe2x80x2-pentahydroxystilbene,
2,2xe2x80x2,4,4xe2x80x2,6-pentahydroxystilbene,
2,3xe2x80x2,4,4xe2x80x2,6-pentahydroxystilbene,
2,2xe2x80x2,4,4xe2x80x2,6,6xe2x80x2-hexahydroxystilbene.
3,4xe2x80x2,5-Trihydroxystilbene, or resveratrol, is the preferred compound according to the invention.
The ascorbic acid analogs are more particularly the salts thereof, especially sodium ascorbate, magnesium or sodium ascorbyl phosphate, the esters thereof, especially the acetic, propionic, palmitic, cinnamic or ferulic esters thereof, or the sugars thereof, especially glycosylated ascorbic acid. Thus, by the term xe2x80x9cascorbic acid compoundxe2x80x9d are intended ascorbic acid itself, as well as the analogs thereof
The ascorbic acid is typically in L-configuration, since it is usually extracted from natural products.
According to the invention, the ascorbic acid and/or the analogs thereof can be used alone or as mixtures of any nature and can be of natural or synthetic origin.
The compositions of the invention are particularly useful for topical application onto the skin and/or mucous membranes.
As indicated above, collagen is involved in the solidity of the dermis, and thus in the firmness of the skin and/or mucous membranes. Also, the fibroblasts are responsible for the synthesis of the proteins of the extracellular dermal matrix, in particular of collagen.
Thus, the present invention features compositions comprising at least one hydroxystilbene in admixture with ascorbic acid, such compositions being well suited to preventively or curatively treat the signs of aging of the skin, more particularly to preventively or curatively treat or combat loose and/or wrinkled skin.
The subject compositions are especially well suited to reduce the signs of aging of the skin, more particularly to reduce the appearance of loose and/or wrinkled skin.
The present invention also features compositions comprising at least one hydroxystilbene in combination with ascorbic acid or analog thereof, for stimulating firming of the skin.
Too, this invention features compositions comprising at least one hydroxystilbene in combination with ascorbic acid or an analog thereof, for promoting the smoothness of the skin and/or to make the skin taut.
In another embodiment of the invention, compositions comprising at least one hydroxystilbene in combination with ascorbic acid or an analog thereof are used to combat the effects of menopause on the skin, more particularly the effects of menopause on collagen and/or fibroblasts.
The amounts of hydroxystilbene and of ascorbic acid or analogs thereof which are administered according to the invention obviously depend on the desired effect.
For example, the amount by weight of hydroxystilbene which can be administered according to the invention advantageously ranges, for example, from 0.001% to 10% and preferably from 0.005% to 5% relative to the total weight of the composition.
To provide an order of magnitude, the amount by weight of ascorbic acid or of analogs thereof which is administered according to the invention advantageously represents from 0.001% to 20% relative to the total weight of the composition, preferably from 0.1% to 15% relative to the total weight of the composition and, more advantageously, from 3% to 10% relative to the total weight of the composition.
In the compositions of the invention, the weight ratio between the hydroxystilbene and the ascorbic acid advantageously ranges from 5xc3x9710xe2x88x925 to 10+4 and preferably from 10xe2x88x923 to 2.
In addition, the compositions of the invention are administered for a period of time which is sufficient to elicit the expected results. To provide an order of magnitude, this period of time can be a minimum of 3 weeks, but can also be more than 4 weeks, or even more than 8 weeks.
The subject compositions are preferably intended for cosmetic or dermatological usage, advantageously cosmetic use.
The compositions of the invention for topical application contain a physiologically acceptable medium, i.e., a medium which is compatible with the skin, including the scalp, mucous membranes and/or the eyes, and can especially constitute a cosmetic or dermatological composition.
The present invention the combination of at least one hydroxystilbene and of ascorbic acid or an analog thereof, to preventively or curatively treat the signs of aging of the skin, more particularly to preventively or curatively treat loose and/or wrinkled skin.
The subject compositions are preferably well suited to reduce the signs of aging of the skin, more particularly to reduce the appearance of loose and/or wrinkled skin.
This invention also features the combination of at least one hydroxystilbene and ascorbic acid or analog thereof for skin-firming applications.
Thus, this invention features the combination of at least one hydroxystilbene and of ascorbic acid or an analog thereof for smoothing the skin or making it taut.
Too, the present invention features compositions comprising at least one hydroxystilbene and ascorbic acid or analog thereof to stimulate the proliferation of dermal fibroblasts.
Lastly, the present invention features compositions comprising at least one hydroxystilbene and ascorbic acid or analog thereof, to combat the effects of menopause on the skin, more particularly the effects of menopause on the fibroblasts.
It will be appreciated that the compositions according to the invention comprise a cosmetically acceptable support (vehicle, diluent or carrier) i.e., a support which is compatible with the skin, mucous membranes, the nails and the hair, and can be in any pharmaceutical form normally used for topical application, in particular in the form of an aqueous, aqueous/alcoholic or oily solution, an oil-in-water or water-in-oil or multiple emulsion, an aqueous or oily gel, a liquid, pasty or solid anhydrous product, a dispersion of oil in an aqueous phase with the aid of spherules, it being possible for these spherules to be polymer nanoparticles such as nanospheres and nanocapsules or more preferably lipid vesicles of ionic and/or nonionic type.
The subject compositions can be more or less fluid and can be formulated as a white or colored cream, an ointment, a milk, a lotion, a serum, a gel, a paste or a mousse. They can optionally be applied to the skin in the form of an aerosol. They can also be in solid form, and, for example, be in the form of a tube or stick. They can be used as a care product, as a cleansing product, as a makeup product or as a simple deodorant product.
In known fashion, the compositions according to the invention can also contain adjuvants and additives that are common in cosmetics and dermatology, such as hydrophilic or lipophilic gelling agents, hydrophilic or lipophilic active agents, preservatives, antioxidants, solvents, fragrances, fillers, screening agents, pigments, chelating agents, odor absorbers, dyestuffs and colorants. The amounts of these various adjuvants and additives are those used conventionally in the fields under consideration, and, for example, constitute from 0.01% to 20% relative to the total weight of the composition. Depending on their nature, these adjuvants and additives can be formulated into the fatty phase, into the aqueous phase, into the lipid vesicles and/or into the nanoparticles.
When a composition of the invention is an emulsion, the proportion of the fatty phase advantageously ranges from 5% to 80% by weight, and preferably from 5% to 50%, relative to the total weight of the composition. The oils, the emulsifiers and the co-emulsifiers formulated into the composition in emulsion form are selected from among those conventional in the fields under consideration. The emulsifier and the co-emulsifier are typically present in the compositions in a proportion ranging from 0.3% to 30% by weight, and preferably from 0.5% to 20%, relative to the total weight of the composition.
Exemplary oils which can be formulated into the composition of the invention, include mineral oils, oils of plant origin (apricot oil, sunflower oil), oils of animal origin, synthetic oils, silicone oils and fluoro oils (perfluoropolyethers). Fatty alcohols (cetyl alcohol), fatty acids and waxes (beeswax) can also be used as fatty substances.
Exemplary emulsifiers and co-emulsifiers include, for example, fatty acid esters of polyethylene glycol, such as PEG-40 stearate and PEG-100 stearate, and fatty acid esters of polyols, such as glyceryl stearate and sorbitan tristearate.
And exemplary hydrophilic gelling agents include in particular, carboxyvinyl polymers (carbomer), acrylic copolymers such as acrylate/alkylacrylate copolymers, polyacrylamides, polysaccharides, natural gums and clays, and exemplary lipophilic gelling agents include the modified clays such as bentones, metal salts of fatty acids, hydrophobic silica and polyethylenes.
The subject compositions can contain other hydrophilic active agents such as proteins or protein hydrolysates, amino acids, polyols, urea, allantoin, sugars and sugar derivatives, water-soluble vitamins, plant extracts and hydroxy acids.
Retinol (vitamin A) and derivatives thereof, tocopherol (vitamin E) and derivatives thereof, essential fatty acids, ceramides, essential oils and salicylic acid and derivatives thereof are representative lipophilic active agents.
According to the invention, in combination with the hydroxystilbene can be associated compounds selected from among:
(1) plant hormones;
(2) calcium antagonists such as verapamil and diltiazem;
(3) OH radical scavengers such as dimethyl sulfoxide;
(4) chlorine-channel openers
(5) plant extracts such as those from Iridaceae, from Rosaceae or from soybean, these extracts also possibly containing isoflavones;
(6) extracts from microorganisms including, in particular, bacterial extracts such as those from non-photosynthetic filamentous bacteria.
Other compounds are also intended, namely, for S example, potassium-channel openers such as diazoxide and minoxidil, spiroxazone, phospholipids such as lecithin, linoleic and linolenic acids, salicylic acid and derivatives thereof described in FR-2,581,542, such as salicylic acid derivatives bearing an alkyl group containing from 2 to 12 carbon atoms in position 5 of the benzene ring, hydroxycarboxylic or ketocarboxylic acids and their esters, lactones and their corresponding salts, anthralin, carotenoids, eicosatetraenoic and eicosatrienoic acids or the esters and amides thereof, and vitamin D and derivatives thereof.
According to the invention, it is also intended, inter alia, to combine the at least one hydroxystilbene with other active agents suited, in particular, for preventing and/or treating a variety of skin conditions. Exemplary such active agents include:
(a) agents which modify skin differentiation and/or proliferation and/or pigmentation, such as retinoic acid and its isomers, retinol and its esters, vitamin D and derivatives thereof, estrogens such as estradiol, kojic acid or hydroquinone;
(b) antibacterial agents such as clindamycin phosphate, erythromycin or antibiotics of the tetracycline class;
(c) agents which modify the adhesion of bacteria to the skin and/or to mucous membranes, such as honey, in particular acacia honey and certain sugar derivatives;
(d) antiparasitic agents, in particular metronidazole, crotamiton or pyrethroids;
(e) antifungal agents, in particular compounds of the imidazole class such as econazole, ketoconazole or miconazole or their salts, polyene compounds such as amphotericin B, compounds of the allylamine family such as terbinafine, or octopirox;
(f) antiviral agents such as acyclovir;
(g) steroidal anti-inflammatory agents such as hydrocortisone, betamethasone valerate or clobetasol propionate, or nonsteroidal anti-inflammatory agents such as ibuprofen and its salts, diclofenac and its salts, acetylsalicylic acid, acetaminophen or glycyrrhetinic acid;
(h) anaesthetics such as lidocaine hydrochloride and derivatives thereof;
(i) anti-pruriginous agents such as thenaldine, trimeprazine or cyproheptadine;
(j) keratolytic agents such as xcex1- and xcex2-hydroxycarboxylic or xcex2-ketocarboxylic acids, their salts, amides or esters, and more particularly hydroxy acids such as glycolic acid, lactic acid, salicylic acid, citric acid and fruit acids in general, and 5-n-octanoylsalicylic acid;
(k) anti-free-radical agents such as xcex1-tocopherol or its esters, superoxide dimutases, certain metal-chelating agents or ascorbic acid and its esters;
(l) anti-seborrhoeic agents such as progesterone;
(m) antidandruff agents such as octopirox or zinc pyrithione;
(n) anti-acne agents such as retinoic acid or benzoyl peroxide;
(o) substances such as antagonists of substance P, of CGRP or of bradykinin or NO synthase inhibitors or alternatively sodium-channel inhibitors, compounds described as being active in the treatment of sensitive skin and as having anti-irritant effects, in particular with respect to irritant compounds which may be present in the compositions.
Moisturizers such as polyols (for example glycerol), vitamins (for example D-panthenol), anti-inflammatory agents, calmatives (allantoin, cornflower water), UVA and UVB screening agents, matt-effect agents (for example the partially crosslinked polydimethylorganosiloxanes marketed under the trademark KSG(copyright) by Shin Etsu), and mixtures thereof are particularly useful active agents.
Anti-wrinkle active agents, and in particular tautening products such as plant proteins and their hydrolysates, in particular the soybean protein extract marketed under the trademark Eleseryl(copyright) by LSN or the oat derivative marketed under the trademark Reductine(copyright) by Silab, can also be added.
Since the skin comprises many more components or constituents than just collagen and fibroblasts, it is found to be advantageous, when a combination of hydroxystilbene and ascorbic acid is used according to the invention, to simultaneously promote the synthesis of these other components, for example such as the lipids, and/or to promote the proliferation of other cell components, for example the keratinocytes.
Thus, this invention features cosmetic compositions comprising, in a cosmetically acceptable medium, a combination of at least one hydroxystilbene and of ascorbic acid or an analog thereof and at least one other active species for stimulating the synthesis of lipids and/or the proliferation of keratinocytes.
In this regard, active species for stimulating the synthesis of lipids which are exemplary are plant hormones, such as auxins, or compounds of plant origin, such as cinnamic acid, and products for stimulating the proliferation of keratinocytes which are exemplary are compounds of plant origin, such as phloroglucinol.
Thus, in addition to hydroxystilbene and ascorbic acid, the compositions according to the invention can comprise cinnamic acid or derivatives thereof and/or a plant hormone, particularly an auxin selected from among indoleacetic acid (IAA), 4-chloroindole-3-acetic acid (4-Cl-IAA), phenylacetic acid (PAA), indole-3-butyric acid (IBA), 2,4-dichlorophenoxyacetic acid (2,4-D), xcex1-naphthaleneacetic acid (xcex1-NAA), xcex2-naphthoxyacetic acid, indolethanol, indoleacetaldehyde and indoleacetonitrile and/or a plant compound such as phloroglucinol.

Hydroxystilbene/ascorbic acid compositions for treating skin afflictions


An aircraft structural panel (10) of the skin-stiffener type such as is commonly used in aircraft construction, has a skin (15) supported by uniformly spaced stiffeners or frames (39). Stiffeners (39) are secured to skin (15) and extend outwardly from the associated skin (15). Each stiffener (39) has a horizontal body (38), an inner mounting flange (41), and an outer bowed flange (42). Mounting flange (41) and bowed flange (42) have free edges and respective inturned beads or curls (44, 46) are formed thereon for stiffening of flanges (41) and (42).

This invention relates generally to a reinforcing support structure for aircraft structural panels of the skin-stiffener type, and more particularly to stiffeners mounted on aircraft panels.
Over the past several years aerospace design engineers have been challenged to address ever higher payload requirements. This has occurred in parallel with weight reduction and other structural efficiency goals that have driven the industry. Ever present safety and structural integrity demands have led the industry to look for more efficient and effective structural members and configurations that are more robust while addressing weight concerns.
Generally speaking, a stiffened aircraft panel""s load-carrying capability is directly related to the type and strength of the stiffener typically installed on one side of the panel. The current approach within the industry to meet higher competitive demands has ranged from resorting to sophisticated alloys including extrudable aluminum and other alloys. It has also included such approaches as using specialty fiber reinforced composite structures, and increasing the depth of conventional stiffener designs as well as the yield strength of the material used in making the stiffeners. In order to appreciate the uniqueness and novelty of the current invention, a better understanding of the current state of the art in addressing the above airframe requirements follows. The first, and most common, approach taken by the industry in addressing the higher requirements has been to make conventional stiffeners out of heavier or higher strength materials. These traditional stiffener designs include the C-channel stiffener and Z-shaped stiffener, as well as the hat-shaped stiffener. Heavier gauges such as 0.055 inch min. (17 gauge) to 0.070 inch min. (15 gauge) material are now common. The use of thicker material has not only lead to greater tooling and handling costs, but also as will be shown, has had the effect of creating other major problems simultaneously.
The aircraft structural panel including any attached stiffeners is a system of parts interacting with each other as they are acted upon by combinations of pressures and in-plane as well as bending loads. Currently, stiffened-panel aircraft structures found in the wings, empennage, and fuselage of aircraft are typically constructed using aluminum or fiber reinforced composite skins with aluminum stiffeners and titanium members, or stiffeners using fiber reinforced composites.
These panels may also be supported by metal stiffeners to provide greater support as the stiffened panel system sustains bending moments as well as in-plane and pressure forces during service. However, an incompatibility occurs when relatively thick, stiffer sections, i.e., stiffeners made of 0.55 inch min. to 0.070 inch min. material are joined or fastened to thinner, less stiff sections, i.e., stringers made of 0.023 inch min. to 0.038 inch min. material. The area where these two sections are joined is an area of load transfer and thus of relatively higher stress. The reason for this is that the stiffer section resists conforming to the deformation of the less stiff stringer sections as loads are increased. The result is that one part of the system, the stringers, try to slide relative to another part of the system, the stiffener. This may result in early failure of the system, such as by buckling of the stiffener or of the stringer. This is due to in-plane compressive loads that result from the constraint that the stiffener imposes on the adjacent members as the loads are increased. Because of the increased stress at the joining area, manufacturers have been forced to modify parts of the stiffened panel to offset this effect. For example, because the use of heavier stiffeners increases the shear load through the joining area or fasteners, especially on the outer extremes of the panel width (near the panel edges), heavier panels and mounting members have had to be introduced. Still another approach to alleviate the problem has been to use additional shear ties or fasteners. This has been implemented in an attempt to reduce the high local in-plane compressive stresses that the heavy stiffeners may impose on the panel skin. However, this approach is undesirable because by increasing the number of parts, it increases the complexity and cost of the system.
This approach requires still heavier stiffeners, since the stiffener failure risk is somewhat reduced when it acts as an independent component rather than as part of a fully integrated system. Another drawback to additional shear ties is that it requires substantially more parts and installation time.
The second approach generally taken by the industry is to make the current hat-shaped and C-channel stiffeners deeper and out of thinner, yet higher yield strength material. This offers the advantage of reducing in-plane stress as noted above while at the same time increasing bending stiffness due to the deeper configuration. However, this approach has major disadvantages.
First, the thinner materials used in these traditional stiffener configurations make these stiffener sections more susceptible to edge stress concentrations. The conventional C-channel, Z-shaped, and hat-shaped stiffeners have a xe2x80x9cblade edge.xe2x80x9d This edge is very susceptible to imperfections in the sheet material along this edge as well as to damage during manufacture, shipping/handling and installation. These imperfections along the blade edge become stress concentration points or focal points at which failure of the stiffener can initiate. A more detailed description of this failure initiation follows.
Even the most perfect, smooth edge of the conventional stiffener will experience a very localized point of high stress gradient due to the characteristic edge stress concentration associated with open sections under bending loads.
Thus, initiation of an edge xe2x80x9cbulgexe2x80x9d or xe2x80x9ccrimpxe2x80x9d on a perfect smooth edge is nothing more than the creation of an edge imperfection that is large enough to grow or xe2x80x9cpropagatexe2x80x9d easily. It is significant that this stress concentration may be made worse by the presence of any relatively small local edge imperfections, even those on the order of size of the thickness of the stiffener material itself.
These imperfections near the edge can be in the form of edge notches, waviness (in-plane or out-of-plane), local thickness variations, local residual stress variations, or variations in material yield strength. Where multiple imperfections occur together, they may all compound together to further increase the stress concentration effect, and thus lower the load level at which failure is initiated. Thus, the existence of any edge imperfections in a conventional stiffener has the effect of enhancing an already established process of failure initiation.
Second, all the above conventional stiffeners, when manufactured out of relatively thin sheet materials are more susceptible to buckling due to the reduced thickness. Buckling is an instability in a part of the stiffener associated with local compressive or shear stresses. Buckling can precipitate section failure of the stiffener. This in turn causes a stress concentration in the adjacent panel skin near the buckled stiffener section, which may cause the stiffened panel to fail.
Finally, some thinner conventional stiffeners can experience xe2x80x9crollingxe2x80x9d when placed under load. Rolling may be caused when the shear stresses within the stiffener result in a net torque about the centroid of the thin walled cross-section thus causing the cross-section to twist, possibly making the stiffener unstable. Another cause of rolling is the curvature of the panel itself that is induced by in-plane or pressure loads that are imposed upon the stiffened panel. Some airframers have increased the cross-sectional length of the flange furthest from the panel skin of the conventional C-channel stiffener in their attempts to solve the rolling problem, but have been met with only marginal improvement. This is because the increased flange length has had the simultaneous effect of increasing the distance from the centroid to the shear center of the channel. Additionally, increasing the cross-sectional flange length caused difficulty in accessing the fastener areas used in mounting the C-channel to the stiffened panel.
The use of solid bulb flange-edges for extruded stiffeners has surfaced as another attempt to address aircraft stiffener needs. However, due to the relative material inefficiency of providing such a solid, mass-intensive edge section, as well as the limitation to specific extrudable aluminum alloys, this solution has not gained extremely wide usage. Because of the higher load requirements of current aircraft, and problems such as the fastening of relatively thick sections to sections relatively less thick, there is a need within the industry today for a new stiffener configuration that can address all of the above mentioned drawbacks and shortcomings of the present state of the art, is suitable for use with substantially all standardized stiffened panel structures, and can be made on a cost-effective basis.
The present invention alleviates and overcomes the above-mentioned problems and shortcomings of the present state of the art through a novel aircraft structural panel stiffener. The novelty and uniqueness of this invention are that it: 1) may be made of thinner material to reduce the in-plane stresses found in the joining area, 2) resists loads adequately to meet new requirements, 3) is resistant to buckling and rolling, 4) effectively addresses edge stress concentrations by modifying the blade edge to an area of relatively low stress, and 5) can be manufactured cost effectively by using conventional manufacturing methods.
This novel invention may be described as a substantially reconfigured or stabilized J-stiffener having a mounting or stabilizing flange. It should be noted here that due to their extreme susceptibility to rolling, conventional J-stiffeners are seldom used in aircraft structural panels. The unexpectedly strong synergisms of the unique characteristics found in the stabilized J-stiffener not only address the above problems, but simultaneously obtain significant material savings. More particularly the synergisms may be described as follows.
The instant invention has substantially redistributed material at critical locations as compared with conventional stiffener configurations. This material redistribution has the effect of altering considerably the behavior of the stiffener as compared with conventional J-stiffeners and other stiffener configurations.
The material redistribution required to accomplish these collaborative effects is accomplished by having specifically placed free edge portions, which are turned inwardly to define tubular beads or curls along the free edges. Moreover it is not just the presence of the tubular bead or curl that enables the substantial level of synergism, but the discovery of specific ratios of curl diameter to other stiffener dimensions that maximize these synergisms even to the extent of obtaining significant weight savings.
Two sets of synergisms combine to make the present invention successful. The first set of synergisms is directly related to the ratio of the diameter of the curl to the stiffener section flange length and web length. Each tubular bead has a cross-sectional dimension which when combined in specific ratios with other stiffener dimensions substantially maximizes the moment of inertia of the overall section about the horizontal and vertical axes with a minimal use of material. Moreover, the tubular bead size specified by these same ratios has the effect of altering the characteristic failure mode normally associated with the free edge stress concentration for conventional stiffeners as described above. Finally, the cross-sectional dimension of the tubular beads of the stabilized J-stiffener make the novel stiffener less sensitive to edge imperfections and damage because the blade edge has now been placed in a position of relatively benign stress levels so that imperfections or damage to the tube or edge region have to be on the order of size of the diameter of the curl in order to have significant detrimental effect to the stiffener section.
Having established the above ratios, a second set of synergisms was discovered by directly combining the above with specific ratios of the stiffener""s cross-sectional web dimension to cross-sectional flange dimension. The compounding effect of the first set of synergisms with this additional set of ratios makes the stabilized J-stiffener more resistant to rolling and buckling and thus avoids the problems that plague deeper conventional structural panel stiffeners using thinner gauge material. Additionally these compounding synergisms make this stiffener unique in that stresses are now more evenly distributed in the flanges thus making the stiffener more stable and less sensitive to dimensional imperfections. Because of these cooperative effects, the stabilized J-stiffener demonstrates its uniqueness and efficiency in using thinner gauge material to reduce in-plane stresses found in the joining area, thus allowing the panel and stiffener to work together as a more cohesive system instead of as individual components.
Because the stabilized J-stiffener effectively addresses the problem of in-plane stresses in the area nearest the panel skin, the use of fewer fasteners may be considered. Thus, the airframer may now uniquely rely upon a single stiffener design to address the stiffening of a wide variety of structural panel constructions.
When compared to conventional stiffeners on the market today, the stabilized J-stiffener uses substantially thinner material while obtaining better resistance to service loads. Thus, even though additional slit width (width of the sheet of material from which the stiffener is made) is required to reposition needed material, the use of thinner gauge material more than offsets the additional slit width, bringing overall material savings as high as 15% in some instances. This innovation in system configuration represents an additional cost savings for the airframer, since material cost is a significant portion of total manufacturing cost of stiffened panel structures. Thus, this unique and novel stiffener is cost effective.
For manufacturing process cost efficiency, the tubular bead is preferably an open-section bead, meaning for example that the sheet material may be formed in an almost complete bend or curl, but the curl need not be closed near its outer edge, such as by welding, bonding, or joining. A closed section tubular bead would work equally well, at a slightly higher fabrication cost.
This edge feature is discussed in more detail as follows. The mounting flange curl and the trough curl are tubular features, preferably open-sections, that are made by shaping the free edges or edge marginal portions of the stiffener cross-sections into an elliptical, preferably circular, cross-sectional shape. As used herein, a circular cross-section is considered to be a special case of an elliptical cross-section. The term xe2x80x9ccharacteristic diameterxe2x80x9d refers to a constant diameter in the case of a circle, while other elliptical shapes will have major and minor axes or diameters, with the minor axis or diameter being the xe2x80x9ccharacteristic diameter.xe2x80x9d
Even though some configurations of a slightly non-circular elliptical shape may be more desirable in some applications, the circular cross-section is generally preferable, because it is simpler to manufacture, while still achieving the desired benefits to a significant degree.
It is important to contrast the edge curl approach against other possible edge treatment approaches by noting that the dimensional order of size effect related to imperfections or damages described above for the curl can not be achieved by simply folding the edge over, either once or multiple times, because in this case the characteristic dimension with respect to the local stresses, will be defined by the fold edge diameter and not by the length of overlap of the fold. This is because the overlap direction is transverse to the edge and quickly moves out of the peak stress region, and because the edge fold diameter defines the maximum distance over which the edge stresses may be effectively spread.
The elliptical or circular open-section tubular shape or xe2x80x9cedge curlxe2x80x9d is contrasted to tubular sections of rectangular cross-sectional shapes, including folded edges, and to open-section tubular shapes of softened corner polygon cross-sectional shapes in that the characteristic diameter with respect to the local stresses, will be defined in each of these other cases by the fold diameter or by the softened corner diameter nearest to the stiffener edge, as opposed to the overall diameter of the edge curl section.
It may be noted that in this context a rectangular or polygonal cross-section with very softened corners or curved sides is in effect an imperfect ellipse or circle.
In some instances, quasi-elliptical or quasi-circular cross-sections, imperfect ellipses, and imperfect circles, in the form of polygon cross-sections with very softened corners may function adequately, but may also be more difficult to fabricate and will be less effective than a generally circular curl. In other cases, the tubular edge may be formed by lapping the edge over itself one or many times in order to achieve specific design objectives within the teachings of the present invention.
Other variations are obtained by including local offsets or adding material locally such as by bonding or welding strips of material or high strength fibers or wires. Still other variations include local modifications to the material such as by heat, electromagnetic, chemical, or deformation treatment of the tubular bead cross-section or of adjacent regions. In spite of the potential for additional fabrication costs, some of the above variations may at times be desirable, for example in local regions where the designer desires local regions of modified cross-sectional shape for space claim, interfacing, or joining reasons. In some applications the curl may be formed by turning the edges through an arc of up to 360 degrees, 720 degrees, or even more, so that the edge loops over one or more times on itself, in order to concentrate mass locally or to address other design objectives. In these cases manufacturing economy and complexity are also considerations.
The resulting synergistic effect of the stabilized J-stiffener""s material efficiency in obtaining the desired bending rigidity or moment of inertia, the alteration of the characteristic failure mode, the reduction in sensitivity to edge imperfections and damage, resistance to buckling and rolling as well as the ability to spread stresses more uniformly has the same degree of compounding advantage as the conventional stiffener""s compounding disadvantage of low resistance to buckling and rolling combined with sensitivity to relatively small edge or dimensional imperfections.
Accordingly, it can now be appreciated by those versed in this art, that the novel stabilized J-stiffener of the instant invention provides a solution to the problems that the airframe stiffened panel art has sought to overcome. Areas of viable application include stiffened panel applications in wing, empennage, and fuselage areas, where they may be used as frame structural members. In these applications the stiffeners are usually installed such that they project in a direction substantially perpendicular to the surface of the panel skin with which they are associated.
In summary, the stabilized J-stiffeners of the present invention having inner stabilizing flanges are uniquely designed to be compatible with substantially all standard stiffened panel configurations, thereby significantly reducing the number of stiffeners and panel frame members that airframers must carry in their inventories and employ, to permit more stringent design criteria to be met, and to permit this to be done without major modification of other associated hardware.
The following description of the present invention may incorporate dimensions that are representative of the dimensions that will be appropriate for most commonly found stiffened panels. Recitation of these dimensions is not intended to be limiting, except to the extent that the dimensions reflect relative ratios between the sizes of various elements of the invention, as will be explained where appropriate.
It is an object of the invention to provide stiffeners for aircraft panels of a minimum weight while maintaining strength requirements.

Stiffeners for aircraft structural panels