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Nine cross-linked UHMWPE acetabular liners were retrieved at revision surgery. Eight of the liners were fully intact and functional at retrieval. Six cases contained shallow initiated cracks at the root of rim notches; one crack had propagated several millimeters. Optical and electron microscopic inspection of the crack surfaces revealed clam shell markings, which are characteristic of fatigue crack initiation. Crack initiation at notches has been identified in reports of catastrophic cross-linked liner failures, with cracks initiation sites exhibiting similar morphology and clam shell markings. Thus, we believe the shallow cracks identified in this case series are precursors to catastrophic rim fracture. The results of this study recommend further investigations to clarify the etiology and prevalence of crack initiation in cross-linked acetabular liners.

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The insensitive explosive PBX 9502 contains 95 wt‐% of TATB crystals and a plastic bonding agent (Kel‐F). The TATB crystals have plate‐like morphology, similar to that of graphite or boron nitride. We have used X‐ray diffraction to measure the preferred orientation (texture) of the TATB crystals in parts fabricated by pressing PBX 9502 powder. Independently, we have used finite‐element calculations to derive the direction and magnitude of the shear imposed during the consolidation of this composite material. Based on our results, we propose that the texture develops because the applied shear causes the TATB crystals to rotate such that their (002) basal planes are parallel to shear planes. The texture predicted by this model agrees qualitatively with that measured at various locations within the PBX 9502 compact. Further validation of this model is obtained by the measurement of the thermal expansion coefficient of PBX 9502, which is highly anisotropic.