Multi-objective design optimization of functionally graded material for the femoral component of a total knee replacement

The optimal design of complex systems in engineering requires pursuing rigorous mathematical modeling of the system’s behavior as a function of a set of design variables to achieve goal-oriented design. Despite the success of current knee implants, the limited life span remains the main concern of this complex system. The mismatch between the properties of engineered biomaterials and those of biological materials leads to insufficient bonding with bone, stress shielding effects and wear problems (i.e. aseptic loosening). The use of a functionally graded material (FGM) for the femoral component of knee implants is attractive because the properties can be designed to vary in a certain pattern to meet the desired requirements at different regions in the knee joint system, thereby decreasing loosening problem. However, matching the properties does not necessarily guarantee the best functionality of the knee implant and there is a need for developing the optimal design of an FGM femoral component that is longer lasting. In this study, therefore, a multi-objective design optimization of a FGM femoral component is carried out using finite element analysis (FEA) and response surface methodology (RSM). The results of using optimized FGM are then compared with the use of standard Co–Cr alloy in a femoral component knee implant to demonstrate relative performance.     

经股四头肌腱关节腔内注射玻璃酸钠治疗膝骨关节炎的疗效观察

目的观察经股四头肌腱行关节腔内注射玻璃酸钠治疗膝骨关节炎(Knee Osteoarthritis,KOA)的疗效。方法对48例KOA患者(70膝)于髌骨上缘经股四头肌腱膝关节腔穿刺注射玻璃酸钠,分别于治疗前及治疗后1月行Hss评分。结果经股四头肌腱膝关节腔穿刺可做到一针穿刺成功。治疗后Hss评分较治疗前明显升高(P<0.01),其中疼痛项、功能项差异有统计学意义。结论经股四头肌腱膝关节腔内注射玻璃酸钠对改善KOA患者临床症状疗效确切、持久,操作简便、成功率高、病人痛苦小。     

Initial fracture behavior of satin woven fabric composites

Final fractures of composites is considered to be caused by cumulation of the microfractures, so that, the initiation of microfracture, namely, initial fracture is important factor to know the mechanical properties. Microfracture behaviors in textile composites were regarded to be decided by the geometry of textile fabric quantitatively. In this study, initial fracture in plain and satin woven fabric composites was investigated and the effect of weaving structure on initial fracture behavior was clarified. First, in order to investigate the geometry of textile fabric, crimp ratio and aspect ratio were measured. Tensile testing was performed and knee point on the stress–strain curve was identified. Fracture process of composites was observed by replica method. Initial fracture in plain woven fabric composite was confirmed as transverse crack in weft fiber bundle, on the other hand, in satin woven fabric composites both transverse crack and filament fracture at the same time was observed. The effects of changes in crimp ratio and aspect ratio on the initial fracture of woven fabric composites were discussed.     

Out-of-plane stability of simply supported beams with knee braces

This paper investigates the buckling of thin-walled beams braced by horizontal knee angles, which is a new practice currently coming into use in Chinese industrial buildings with small and moderate overhead cranes of light or medium duty to improve the stability of simply supported crane runway girders. It was found that this technique increases significantly the elastic buckling capacity of thin-walled beams. The increase in elastic-plastic buckling capacity may also be as high as 40% compared with unbraced beams. Simple formulae are presented for buckling moments of the knee-braced beams. Compared with the results of finite element analysis, the proposed formulae have excellent accuracy in prediction of the critical loads of knee-braced beams under concentrated load at mid-span and uniformly distributed loads. The application of the formulae was explained through an example of a practical crane runway girder.     

On the characteristics of new ductile knee bracing systems

In this paper, a new structural lateral bracing system called ‘Chevron Knee Bracing’ (CKB) is investigated. This new form of framing system is constructed through the knee and the diagonal brace elements. The knee part is a fuse-like component that dissipates energy by the formation of plastic flexural and/or shear hinges at its ends and mid-span, when the building is subjected to severe lateral loads. However, the diagonal brace component, on the other hand, provides the required level of lateral stiffness and remains in the elastic range without buckling at any time. In this investigation, first, by studying of the system in the elastic region, three new and practical parameters are established. Then, the best fitting optimal shape and angle of the knee and brace elements are projected, analytically. In the next step, by developing a nonlinear analytical knee element model, the actual behavior of this new CKB system is experienced in the nonlinear static and dynamic analysis, on two example structural systems, where the knee element happens to be in the moment and/or shear yielding mode. Using the results on nonlinear analysis of these test problems, the main properties of the CKB, such as the energy dissipation characteristics of the proposed systems, are properly inspected by establishment of an energy calculation algorithm. Finally, based on the presented optimal shape of the CKB in this paper, two step-by-step algorithms accompanied by appropriate main graphs and charts are suitably demonstrated and nonlinear behavior of the new model for flexural and shear yielding modes is well determined, which is followed in the next paper.     

Behaviour of semi-rigid steel beam-to-beam joints under bending and axial forces

This paper presents an analysis of semi-rigid beam-to-beam end-plate bolted joints that are subjected to bending and tension or a compression axial force. Usually the influence of axial force on joint rotational stiffness is neglected. According to EC3, the axial load, which is less than 10% of plastic resistance of the connected member under axial force, may be disregarded in the calculation of characteristics of a joint. Actually, the level of axial forces in joints of structures can be significant and has a significant influence on characteristics of semi-rigid joints. One of the most popular practical methods permitting the determination of rotational stiffness and moment resistance of a joint is the so-called component method. The extension of the component method for evaluating the influence of bending moment and axial force on the rotational stiffness and moment resistance of a joint are presented in the paper. The numerical results of calculations of characteristics of joints and calculations of steel framework are presented in this paper as well.