关键词： AZ31镁合金   载流静轴   肩搅拌摩擦焊   数值模型   温度场   应力场  

摘要： 传统镁合金搅拌摩擦焊接过程中材料流动性能较低,从而焊缝容易出现缺陷。本文利用COMSOL仿真软件,建立一种镁合金载流静轴肩搅拌摩擦焊(SSFSW)双热源数值模型,研究输入电流对材料流动性能的影响。通过改变输入电流参数进行数值模拟得到焊接过程温度场,应力场和速度场的演变规律。发现随着电流的提高,温度场分布沿焊缝厚度方向趋于均匀化,焊缝的温度梯度降低,应力场峰值从532 MPa降低至461 MPa,呈明显降低趋势,证明此时焊缝中材料流动性得到显著提高。在电流达到150 A时,焊接温度峰值接近于材料熔点650℃,在此温度下易于得到无缺陷的焊缝和性能优异的焊接接头。数值模拟有效地预测实际焊接实验中可能会出现的结果,减少为了得到合理焊接参数所需大量实验的成本,并且仿真结果对工艺参数的选择有重要的指导意义。

关键词： 跟骨骨折   骨不连   硫酸钙人工骨   个案分析  

摘要： 跟骨位于足的后方,是足部跗骨中最大的一块骨骼,骨皮质较薄,内部的骨小梁稀疏。跟骨骨折占全身骨折的2%,约75%为关节内骨折,多由坠落伤或暴力挤压导致,骨折后局部剧烈疼痛、肿胀,皮下可见淤血,常伴脊柱、骨盆等部位骨折。骨折若复位不良,会引起创伤性关节炎,导致足部疼痛、功能障碍,致残率较高。无移位的跟骨骨折可选择保守治疗,小腿石膏托制动固定4~6周,待临床愈合后即拆除石膏,一般在伤后12周以后下地行走。对于严重的关节面损伤伴压缩的骨折治疗比较困难,为了避免复位后位置的丢失在跟骨外侧入路切开复位钢板螺钉内固定基础上可以进行植骨。植骨材料可以使用自体骨、异体骨或人工骨材料。本文希望通过对1例植入硫酸钙人工骨致跟骨骨折术后骨不连的病例进行分析,总结更多的经验。

关键词： AZ31B镁合金   矫直   拉压不对称性   中性层偏移  

摘要： 基于CaBa2004拉压不对称性屈服准则,从弹塑性力学角度对AZ31B镁合金板材矫直过程进行了分析,推导出AZ31B镁合金板材在矫直过程中中性层偏移量计算公式。该公式表明中性层偏移量与弹区比和板厚密切相关。通过与数值模拟结果对比,分析了理论值和数值模拟结果的误差及造成误差的原因。说明了AZ31B镁合金板材在矫直过程中存在中性层偏移现象。受拉压不对称性的影响,镁合金板材在受载过程中,中性层向受拉方向偏移。运用理论推导和数值模拟计算分析,得出了不同压下量下的镁合金板材的中性层偏移量大小,确定了镁合金板材在矫直过程中中性层偏移规律。

关键词： AZ91 magnesium alloy   Gd   slow strain rate tensile test   stress corrosion cracking  

摘要： AZ91 and AZ91-xGd (x = 0.5, 1.0, 1.5 wt%) magnesium alloys are extruded into plates. The addition of Gd promotes the formation of Al2Gd, effectively reducing the volume fraction of the beta-Mg17Al12 phase and making the banded structures of the extruded magnesium alloys thinner. The corrosion weight loss tests and electrochemistry analyses demonstrate that Gd significantly improves the pitting resistance of the AZ91 in 3.5-wt% NaCl solution saturated with Mg(OH)(2). Slow strain rate tensile tests show that in a corrosive environment, compared with AZ91, the elongation to failure of the AZ91-1.0Gd alloy is increased by 47%, and the alloy exhibits excellent stress corrosion resistance in this study. The fracture mode of AZ91 is changed from typical intergranular fracture to a mixture of transgranular and intergranular fracture in the corrosion solution by adding Gd. The mechanism of Gd to improve the stress corrosion resistance of the AZ91 magnesium alloy is that Gd increases the corrosion resistance, especially the pitting of AZ91.

关键词： Bionic internal fixation   Finite element analysis   Gamma nail   Intertrochanteric fracture   Trabecular bone  

摘要： Objective To using finite element analysis to investigate the effects of the traditional titanium alloy Gamma nail and a biodegradable magnesium alloy bionic Gamma nail for treating intertrochanteric fractures. Methods Computed tomography images of an adult male volunteer of appropriate age and in good physical condition were used to establish a three-dimensional model of the proximal femur. Then, a model of a type 31A1 intertrochanteric fracture of the proximal femur was established, and the traditional titanium alloy Gamma nails and biodegradable magnesium alloy bionic Gamma nails were used for fixation, respectively. The von Mises stress, the maximum principal stress, and the minimum principal stress were calculated to evaluate the effect of bone ingrowth on stress distribution of the proximal femur after fixation. Results In the intact model, the maximum stress was 5.8 MPa, the minimum stress was -11.7 MPa, and the von Mises stress was 11.4 MPa. The maximum principal stress distribution of the cancellous bone in the intact model appears in a position consistent with the growth direction of the principal and secondary tensile zones. After traditional Gamma nail healing, the maximum stress was 32 MPa, the minimum stress was -23.5 MPa, and the von Mises stress was 31.3 MPa. The stress concentration was quite obvious compared with the intact model. It was assumed that the nail would biodegrade completely within 12 months postoperatively. The maximum stress was 18.7 MPa, the minimum stress was -12.6 MPa, and the von Mises stress was 14.0 MPa. For the minimum principal stress, the region of minimum stress value less than -10 MPa was significantly improved compared with the traditional titanium alloy Gamma nail models. Meanwhile, the stress distribution of the bionic Gamma nail model in the proximal femur was closer to that of the intact bone, which significantly reduced the stress concentration of the implant. Conclusion The biodegradable magnesium alloy bionic Gamma

关键词： magnesium alloy AZ31B   shot peening   mechanical properties   depth of penetration   ballistic resistance  

摘要： The effect of shot peening on mechanical properties and ballistic resistance of plates from magnesium alloy AZ31B 25 x 300 x 300 mm in size to the piercing action of a projectile (diameter 7.62 mm, velocity 690 m/sec) is studied. The yield strength, the ultimate strength, the elongation, the impact toughness and the microhardness of the alloy are determined prior to and after shot peening with glass beads. The surface of the internal channel of penetration of the projectile is investigated by scanning electron microscopy. The shot peening is shown to have a positive effect on the ballistic resistance of targets from alloy AZ31B.

关键词： Engineering Thermodynamics   Heat and Mass Transfer   Industrial Chemistry/Chemical Engineering   Thermodynamics  

摘要： The estimation for interfacial heat transfer coefficient (IHTC) between casting and mold is paramount to predict solidification phenomena. In this study, three hydraulic pressures of 30, 60, and 90 MPa were applied to indirectly squeeze cast magnesium alloy AZ91 in a P20 steel mold with five casting section thicknesses of 2, 4, 8, 12, and 20 mm, named steps 1, 2, 3, 4 and 5, by using a 75-ton hydraulic press machine. For comparison, the AZ91 alloy was also cast without the applied pressure (0 MPa). K-type thermocouples were utilized to measure temperatures simultaneously on the casting surface and at three different depths from the mold surface inward. Based on the temperature measurements, the IHTCs at the five steps were calculated by the inverse method. Despite of the differences in their peak values, the IHTC variation for the three applied pressures at the five steps during the squeeze casting process was similar to that of 0 MPa, in which the IHTC values abruptly rose to an apex first, and then declined slowly. The overall IHTC values of step 5 were higher than those of the other four steps, while the lowest peak IHTC value was present at step 1. When the applied pressure was increased, the IHTC peak value of each step became large accordingly. The empirical equations relating the IHTCs to the pressures, section thicknesses, and temperatures at the casting/mold interface were derived based on the multivariate linear and polynomial regression.

关键词： 生物医学工程   镁合金   金属材料   表面改性   研究  

ISBN: (纸本)9787122394545

摘要： 本书内容结合了当今国内外对磁控溅射表面改性材料的研究以及发展情况，着重介绍了近年来作者在磁控溅射表面改性材料方面的基础理论知识的学习、实验材料与方法、制备工艺流程、分析检测方法以及相关的国内外先进技术手段的研究。主要内容包括：镁合金表面直流磁控溅射Ti-TiN镀膜研究、镁合金表面高功率磁控溅射Ti（Si）-TiN-Ti（Si）N镀膜研究、直流磁控溅射制备Ta膜及其性能分析、高功率脉冲磁控溅射制备Ta膜及其性能分析、高功率脉冲磁控溅射制备多层膜及性能分析。 本书涉及多门学科，可为研究磁控溅射表面改性材料的相关人员提供意见和建议，并且为材料领域的研究与应用提供参考资料。

关键词： Microstructures   Thermomechanical processes   Crystal plasticity   Dynamic recrystallisation  

摘要： In this paper, a dynamic recrystallisation (DRX) viscoplastic self-consistent (VPSC) model is created to predict the continuous DRX (CDRX) and twin-assisted DRX (TDRX) behaviour within an AZ31 magnesium (Mg) alloy over temperatures ranging from 25 degrees C to 200 degrees C. At this temperature range, the active deformation mechanisms and physical phenomena participating in the strain accommodation and texture evolution of Mg alloys are: a basal slip, a prismatic slip, c + a pyramidal slip, {1012} tensile twinning, and DRX. In order to predict which deformation modes are activated for this particular alloy and their influence on the DRX mechanism, a temperature sensitive VPSC model combined with a dislocation density hardening law and a composite twin grain model is used. The model is validated against a comprehensive set of experimental data including flow curves and texture evolution, realised on a hot-rolled AZ31 Mg alloy deformed at different temperatures between 25 degrees C and 200 degrees C under uniaxial tensile loads parallel to, perpendicular to, and at 45 degrees offset from the rolling direction of the processed material. Furthermore, a parametric study into parameters such as grain size, dislocation density, and crystallographic orientation of the nucleating DRX grains influencing the DRX kinetics and, subsequently, the plastic material behaviour of the alloy is carried out and discussed.

关键词： MgY12Zn2,5   extrude   solid solution treatment   microstructure   mechanical properties  

摘要： The microstructural evolution of MgY12Zn2,5 magnesium alloys was observed, and the strengthening and toughening mechanism of the alloys were studied. The results showed that the MgY12Zn2,5 alloy after solution treatment with higher content of H-14 - LPSO (long - period stacking - ordered structures) could more effectively inhibit the recrystallization and growth of recrystallized grains, and the microstructure was more fine and uniform. And its tensile strength (R-m), yield strength (R-v) were 395 MPa, 308 MPa and elongation (A) 17,5 %, respectively. In contrast, the MgY12Zn2,5 alloy treated at 470 degrees C for 24 h, whose R-m, R-v, were only 376 MPa, 282 MPa and A 15,5 %, respectively.