Purpose Core Bone Plug Fixation (CBPF) technique is an implant-less methodology for ACL reconstruction. This study investigates the effect of bone density on CBPF stability to identify the bone quality that is likely to benefit from this technique. Methods Artificial blocks with 160 (Group 1), 240 (Group 2), and 320 (Group 3) kg/m3 densities were used to simulate human bone with diverse qualities. These groups are representative of the elderly, middle age and young people, respectively. A tunnel was made in each test sample using a cannulated drill bit which enabled harvesting the core bone plug intact. Fresh animal tendon grafts were prepared and passed through the tunnel, so the core bone was pushed in to secure the tendon. The fixation stability was tested by applying a cyclic load following by a pullout load until the failure occurred. The selected group was compared with interference screw fixation technique as a gold standard method in ACL reconstruction. Results The Group 2 stiffness and yield strength were significantly larger than Group 1. The graft slippage of Group 1 was significantly less than Group 3. The ultimate strengths were 310 N and 363 N, in Groups 2 and 3, significantly larger than that of Group 1. The ultimate strength in fixation by interference screw was 693.18 N, significantly larger than the bone plug method. Conclusions The stability of CBPF was greatly affected by bone density. This technique is more suitable for young and middle-aged people. With further improvements, the CBPF might be an alternative ACL reconstruction technique for patients with good bone quality. Clinical relevance The CBPF technique offers an implant-less organic ACL reconstruction technique with numerous advantages and likely would speed up the healing process by using the patient’s own bones and tissues rather than any non-biologic fixations.

The aim of this paper is to investigate the effect of geometrical parameters on the performance of jet penetration in the process of shaped charge. To this end, the finite element analysis was used to simulate the process. The simulated process was validated by experimental tests and the effect of some parameters including stand-off distance and the liner thickness on the jet penetration depth was studied. The results indicated that choosing the optimal distance between the liner and the target (stand-off distance) can significantly affect the performance of jet penetration in the target. In addition, examining the effect of liner thickness on the penetration depth efficiency revealed that by decreasing the liner thickness, the jet penetration depth on the target increases. It should be noted that ABAQUS finite element software was used in this simulation to analyze the process of shaped charge.

No abstract

Thermosonic tests are capable of detecting surface defects such as fatigue cracks. The mechanism of its operation is based on the stimulation of structural vibration of the test piece which generates detectable displacements between crack surfaces. The main problem with using a thermosonic test is the uncertainty caused by chaotic and non-reproducible vibrations of the test piece. Consequently, the study of effective parameters such as, for example, the frequency and amplitude of vibration, crack size, vibration damping around the crack, and acoustical chaos could play a major role in improving this method to make it a highly reliable non-destructive test. In this study, an algorithm has been used to estimate the wasted vibration energy caused by extra damping due to the presence of cracks in the sample. Initially, the validity of the discussed algorithm is studied and findings compared with the results of other experimental studies available in the literature. Subsequently, a simulation process of the thermosonic test in a beam in two conditions of chaotic and non-chaotic vibrations take place. Then, findings are compared with the desired algorithm. Results indicate that in a non-chaotic vibration condition, the measured wasted energy by the algorithm is confirmed by the results obtained from the finite element. However, in a chaotic vibration condition, when the crack size is large enough, there is considerable difference between the results of the finite element method and the algorithm. This difference is due to the occurrence of acoustic chaos while stimulating the test piece. The used algorithm was unable to predict this.