Abstract
Flatwise tension strength of sandwich structure is important for designing a sandwich construction since it provides failure mechanism and debonding strength between the skin faces and the core, as well as (i) core strength and (ii) face strength of the sandwich structures. The flatwise tension strength is affected by many factores: method of core preparation, test environment, testing speed, etc. In this paper, the ambient test temperature was 23 deg C and the humidity was 65%. The testing speed was 0.5 mm/min. Four different core preparations were investigated. ASTM C297 was used as a standard method to get the strength values. Two processes were employed to cure the adhesive during coreto-face bonding. It was found out that cleaning the core with Methyl-ethyl-ketone (MEK) and drying further in an oven gives maximum flatwise tension strength of the sandwich structures, with the value of 5.9 MPa. The data base is important for both the manufacturing and design engineers. For the manufacturing engineers, the data provides a value for process qualification, while for design engineers it gives a maximum allowable strength for designing sandwich construction for tensile loads.
Data
The data set provided herein was the result of experimental studies conducted to determine flatwise tensile strength of sandwich structures prepared using different methods of core material preparation and the core-to-face adhesive curing methods. The type of materials for sandwich structures is given in Table 1 , while the core material preparation parameters are given in Table 2 . A strength-deformation curves produced during the flatwise tensile tests were given in Fig. 4 , while the complete maximum flatwise tensile load and strength was given in Table 3 for configuration parameters A, B, C and D. All specimens with different parameters were able to withstand above 5 MPa, with configuration B achieved the maximum flatwise tensile strength of 5.59 MPa. Fig. 5 provides failure surface of typical specimen configuration after test. The failure mode is a combination of adhesive, cohesive and core failure according to ASTM C297 [1] . The complete pictures of failure surfaces for each specimen is available from http://bit.ly/DIB-Data-Flatwise-Test. Table 4 gives summary of the failure modes of the specimens.
Experimental design, materials, and methods

Experimental design
The experiments were carried out according to ASTM C297 [1] . Typical experimental setup is given in Fig. 1 [1, 2] , while the current experimental configuration is given in Fig. 2 . Specifications Table   Subject Aerospace Engineering  Specific subject area  Sandwich structures, Flatwise tension, Mechanical properties, Composite materials  qualification  Type of data  Table  Image Chart How data were acquired Laboratory experiment using Universal Testing Machine and a special apparatus for flatwise tension test Data format Raw Parameters for data collection Different core preparations: 1) core material was cleaned using Methyl-Ethyl-Ketone (MEK) spray without drying process, 2) core material was cleaned using MEK spray with drying process in an oven, 3) core material was cleaned using air spray without drying process, 4) core material was cleaned using air spray with drying process in an oven. Two methods to cure the adhesive during core-to-face bonding: table press and autoclave.
Description of data collection
Specimens with special apparatus according to ASTM C297 were put into the Universal Testing Machine and loaded in tension. The maximum load and the load-displacement curve were recorded before failure. This was done for different core preparation parameters.
Data source location
Bandung, Indonesia Data accessibility Date are accessible in this article. The complete raw data is available in http://bit.ly/DIB-Data-Flatwise-Test
Value of the Data
The data set can be used as a reference concerning the flatwise tensile strength of core materials used for sandwich satructures incorporating carbon/epoxy composite faces. The manufacturing engineers will use the data for process qualification in sandwich structures, while the design engineers will use the data for designing sandwich structures in order to avoid the debonding failure between the skin and the core in sandwich construction. The dataset allows exploration on the use of different adhesive materials and core preparations to get the maximum flatwise tensile strength of sandwich materials.
Value of the Data
The dataset provides an insight into the debonding failure between the skin and the core in sandwich construction.
Table 1
List of materials.
Parts Type of materials used
Face Hexcell W3T282-42 00 -F593 carbon fibre epoxy fabric prepreg. Core
Parts Type of materials used
Hexcell HRP-3/16-4.0 fibre glass honeycomb core with phenolic resin Core-to-face adhesive Cytec FM-300 M.03 epoxy film adhesive Aluminum-to-face adhesive Cytec FM-73 M.06 epoxy film adhesive Table 2 Core material preparation parameters and the specimens numbering system.
Spec Code
Core material preparation parameters Spec number 
Materials
The materials used in the experimental was given in Table 1 . The materials properties are as follows:
Materials
Core: Fibreglass honeycomb core, HRP-3/16-4.0 Hexcell with the cell size of 3/16 inch and the density 0.064 g/cm 3 . The shear strength in L-direction is typically 4.07 MPa and the modulus 90 MPa; while in the W-direction, the strength is typically 1.10 MPa and the modulus is 45 MPa [3] . The thickness of the core was 12.7 mm. Core-to-face adhesive: FM-300 M.03 epoxy film adhesive Cytec Engineering Materials. The thickness of each ply was 0.13 mm with the density of 0.025 g/cm 3 . The service temperature was À55 deg C up to 135 deg C. The curing temperature was 170e185 deg C. Two plies of adhesive film was needed during the experiment. Face: carbon fibre fabric epoxy prepreg W3T282-42 00 -F593 Hexcell. The tensile strength was 3530 MPa and the modulus was 230 GPa. The thickness for each ply was 0.21 mm. Two plies of carbon/ epoxy fabric was needed to produce the faces. Aluminum-to-face adhesive: FM-73 M.06, epoxy film adhesive Cytec Engineering Materials. The thickness of each ply was 0.25 mm and the density was 0.025 g/cm3. The service temperature was À55 to 80 deg C, while the curing temperature was 120e130 deg C. 
Manufacturing
The specimens manufacturing are the followings:
Manufacturing
1) The carbon composite skin facing was manufactured using 2 plies Hexcell W3T282-42 00 -F593 Carbon fibre epoxy fabric prepreg and cured in an autoclave with temperature of 180 ± 5 deg C and Core failure DA5 Core failure and cohesive failure hold for 2 hours at the pressure of 3 bars. The heating up rate was kept between 1 and 3 deg C/min, while the cooling rate was kept below 3 deg C. 2) The core material was Hexcell HRP-3/16-4.0 Fibre glass honeycomb core with phenolic resin. Fig. 3 shows core material used in the experiments. The core material was prepared using different parameters as given in Table 2 . The cleaning process with MEK was carried for 1 minute. The cleaning process with air gun was also done in 1 minute. The drying process was done using oven for 2 hours with temperature of 100 deg C.
Manufacturing
3) The skin face and the core were bonded together using adhesive film Cytec FM-300 M.03 Epoxy film adhesive and cured. The curing process used two methods: using hot table press and autoclave. The curing was done at the temperature of 120 deg C. In the table press, the specimens was vacuumed to 200e250 mmHg (0.266e0.333 bar); with a pressure of 1.70 bar for 2 hours. The same parameters were done in the autoclave process. 4) The resulted sandwich structures are then bonded to the aluminium block using Cytec FM-73 M.06
Manufacturing
Epoxy film adhesive and cured once again in table press at the temperature of 120 deg C for 2 hours. The aluminum block was sandblasted before bonded was carried out to the faces. The resulting sandwich structures were ready for flatwise tension tests.
Flatwise tensile test methods
The specimen was put into the Universal Testing Machine and given the tensile load. Fig. 1 shows typical flatwise tensile experimental setup. The specimens dimension was 50 Â 50 mm and the overall thickness is 94 mm. The tensile machine was Instron with the maximum capacity of 100 kN. The displacement rate was set to be in the order of 0.5 mm/minute. Fig. 1 shows the experimental setup. The maximum load and the load-displacement curve were obtained after the test.
Flatwise tensile test methods
The ultimate flatwise tensile strength was determined using the Eq. (1):
Flatwise tensile test methods
where: F ftu z : flatwise tensile strength P max : ultimate tensile load A: area of the specimen. In this case 50 Â 50 mm. It was known that the flatwise tensile strength was affected by the environment [4] and discolouration occured when using Cytec FM-200 adhesive [5] . The environment affect the bondline strength of core-to-face adhesive. Cocured sandwich structure provided more consistent data than precured [6] . In this paper, the tests were done with the room temperature of 23 deg C and the humidity was 65%. The faces were precured before adhesively bonded to the core.

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