PICA-X is a SpaceX proprietary variant on the NASA Ames developed PICA (Phenolic Impregnated Carbon Ablator) heat shield material. NASA quotes decades of rigorous research, testing and development that went into it, and on this photograph we see PICA tested with the use of NASA Ames' arcjet:
NASA Ames' arcjets were integral to the testing of the PICA thermal protection material. Credit: NASA Ames
SpaceX additionally worked on it with Dan Rasky, one of the original developers of the PICA material, to develop the new PICA-X material. But how does PICA-X differ from its predecessor PICA, which, while it has some fantastic thermal properties, is really light and an improvement over FiberForm®, is also structurally rather weak (PDF) and can still grow fractures in the matrix when subjected to thermal and mechanical loads during both launch and atmospheric entry?
Matrix cracking in charred PICA samples. Source: Fracture in Phenolic Impregnated Carbon Ablator, NASA Ames Moffett Field, 2011
To what degree has SpaceX managed to improve on PICA material characteristics with their proprietary PICA-X? Has it been tested for typical stress loads aboard Falcon 9 to LEO and reentry, and what were the results in terms of both comparing PICA and PICA-X and potential reuse cycle?
I realize that I'm asking about proprietary technology that not much might be known about yet, but I'm looking for stress test results of a material that will support human spaceflight in the near future and surely SpaceX will have much reassuring to do that their technology is safe and performs as expected also in real life. So I expect at least some research of PICA-X eventually also published. Please no speculations, I'm perfectly happy to wait for answers that can be supported by facts and references, once they become available.