This paper aims to investigate the dynamic characteristics of a loading stage with a rolling guide. In practice, the rolling guide is designed with different contact geometries to withstand various loads in service; it forms a rolling interface with contact stiffness varying with the applied loads. To model the rolling contact mode realistically, different contact modes were assumed at the interfaces between the ball and raceway and simulated by using spring elements with stiffness calculated by using the Hertzian contact theorem. The vibration characteristics of the rolling guide were determined by the proposed method and successfully verified by experimental vibration tests. As validation of the proposed method, a loading stage with rolling guides was also demonstrated to have different dynamic characteristics as various loads were applied, with the results from the experiments correlating to the finite element simulations.
The function of curve offset is of importance in the process of generating a machining tool-path. The robustness of curve offset is compact with reliable invalid loops removal algorithms. The traditional method based on interference detections in searching for all contact positions is a time consuming process and prone to misunderstanding. In order to improve such removal function, a new algorithm called the forward locus tracing method (FLTM) was introduced here. The FLTM searches for all intervals split by intersections of complicated planar curves directly and transforms 2D transversal intersection problems into 1D interval identifications. This proposed mapping process in FLTM may simplify the structure of tasks and be implemented by a computer program easily for CAD systems. Some examples with multiple loops were demonstrated and the results present considerable efficiency and reliability in the offset operation
This study was aimed at investigating the effect of the bone compositions on the fracture toughness of bovine cortical bone. A series of the SENB bovine cortical bone specimens were tested to assess the fracture toughness. Dual energy X-ray absorptiometry (DEXA) was applied to determine the mineral content of each bovine cortical specimen and hence the porosity and bone mineral fraction were measured. Current results indicate that the mean value fracture toughness is 9.37 MNm3/2. Moreover, the fracture toughness was found to be significantly correlated with the apparent wet bone density and porosity of bone structure. No apparent correlations are found among clinical BMD and mechanical properties, implying that the BMD is an invalid indicator of the bone properties. Additionally, the tested data were fitted to the relationship, based on power law model, that the fracture toughness increase as a power (1.526) of increasing volume fraction and as a power of increasing bone mineral fraction (0.8195). These data indicate that small changes in the amount or density of compact bone tissue exert a more pronounced influence on fracture property.
Clinical studies have proved that artificial joints may fail under prolonged gait load, which failure mechanism includes mechanical loosening and infectious loosening. Infectious loosening can be prevented by avoiding osteomyelitis, caused by bacterial infection arising from the marrow cavity, which affects the fixation function of the bone handle. As a result, use of bone cement containing various antibiotics has become an important method for prevention and treatment of infection after artificial joint replacement. This study was aimed to investigate the mechanical properties of bone cement after the addition of antibiotics through the mechanical tests. With the measurements we can then assessed the variations of mechanical strength with the dosage of antibiotics. The results showed that the dose of antibiotics directly affected the compression strength and elastic modulus of antibiotic bone cement. When the antibiotics was added more than 4.8 wt %, the cement strength was obviously affected and reduced, by 27%, indicating that during artificial hip joint replacement, the dose of antibiotics should be concerned, in order to avoid affecting the strength of bone cement and stability of the entire implant.
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