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A shaft suddenly suffered fracture during the test of loading in three directions. The shaft was made from 30CrMnSiA steel. The failure cause was analyzed by visual, stereo, and scanning electron microscopic observations of appearance and fracture surface of the shaft, micro-area composition inspection, metallographic examination, and measurement of the hydrogen content. The results showed that the failure mechanism of the shaft was fatigue fracture resulting from hydrogen-induced intergranular microcracks. The hydrogen-induced cracks were mainly caused by abnormal pickling during production of the shaft.

Mandibular destruction resulting from tumours, trauma, congenital, ankylosis and other reasons leads to disturbed masticatory function. The ideal goal would be to reconstruct a condyle that is similar to the original. However, each of the condylar reconstruction approaches in current has specific shortcomings. Tissue engineering can provide a method to overcome these difficulties. A tissue-engineered mandibular condyle composed of bone and cartilage has been reported, but the strength and shape of the scaffolds used cannot meet the requirement of the clinical use. Freeze-dried allogenic condylar bone is biocompatible, bioresorbable of low antigenicity and provides the morphology for the condyle similar to the original. It is a good scaffold material for tissue engineering. The three-dimensional porous internal titanium scaffold is also biocompatible; it can be easily made into the shape that we need. The two scaffolds have sufficient mechanical strength before no bone formation. Hence, we hypothesise using a three-dimensional porous titanium scaffold or an allogenic bone scaffold combined with osteogenic, chondrogenic material and bone marrow stromal stem cells in vivo tissue engineering to repair condylar defects. This article discusses the hypotheses.

The effect of frequency and sample shape on fatigue behaviors of DZ125 superalloy are systematically studied. The results show that fatigue fracture still occurs above the cycle of 108 for tests carried out at the frequency of f = 20 kHz and stress ratio R = −1, so the traditional fatigue limit at cycle of 107 is not appropriate for fatigue design. Fatigue fracture surfaces are perpendicular to stress axis for cylindrical and plate specimens, and the fatigue cracks originate from the extra surface of the specimens. Fatigue crack is apt to propagate from cutting direction to forward direction, which occurs mainly in the second propagation stage at higher stress amplitude. There is an obvious frequency effect for DZ125 superalloy. The higher the test frequency is, the more serious the effect of frequency on fatigue behaviors of the alloy. After the frequency correction, the ultra-high cycle fatigue S-N curve well coincide with the traditional fatigue S-N curve.