Are there known life forms that are able to transform mechanical energy into chemical energy?
There are no known life forms that use mechanical energy as a primary form of metabolic energy (i.e., for generic cellular functions). Many life forms are sensitive to mechanical disruption in some way, so they do utilize mechanical energy, but in a very limited fashion (@David's answer touches on this), and of course many organisms have life cycles that somehow depend on mechanical transportation (seed/spore dispersal, traveling on the wind or ocean currents, etc).

I think the main physical problem is that mechanical energy just isn't available to biological cells in a form that can be converted to substantial chemical energy. They are small, and tend to have other great benefits for being small.

To use an ocean wave as an example, there is very little or no perceptible movement for a cell in that wave, besides an apparent increase and decrease in the force of gravity. The top and bottom of the cell are moving together with the flow of water, so there is no differential to operate on.

An E. coli weighs about 1 picogram. If it could capture all of the energy from falling from 1km in the air on earth, assuming no uncaptured aerodynamic drag, that would be about 10-11 joules.

If there are ~3000 kJ/mol of energy available from burning glucose, that means about 5 &times; 10-21 joules per molecule of glucose, so about 20 billion glucose molecules, which sounds like a lot but it is only 1 femtogram, 0.1% the weight of the cell.

Also note: in @David's answer he makes a very good point that in a way, using mechanical force to open a channel is indeed a form of energy usage and therefore a proof of concept that this could happen. To put that process in the same ballpark, this source (originally mentioned by @GerardoFurtado) gives the work necessary to open one of these channels at around 8 &times; 10-22 joules. The open latency for those channels is under 50 microseconds, but that still greatly limits the number of possible cycles per unit time. Chemical energy is just substantially more dense than mechanical energy is: that's why gunpowder superceded catapults (and even the trebuchet..).