复合材料支架的仿生界面设计与有限元优化方法

研究光固化成形复合材料支架的材料界面分层问题。以关节软骨下骨板为仿生对象,提出骨软骨复合材料支架的界面结构仿生设计与优化方法。在构建关节软骨下骨板表面孔隙结构模型(面孔隙率为6.7±0.71%,孔隙分布夹角为40°~50°或80°~90°)的基础上,建立PEGDA/β-TCP软骨复合支架的仿生界面结构模型和有限元分析模型。结合多目标优化方法确定影响骨体孔隙成形性及其与软骨层分层的关键参数为孔隙直径、结构单元(三边形、四边形、六边形)、孔隙间距(边长)、面孔隙率;确定具有四边形结构单元,面孔隙率为5%~15%,孔隙尺寸为不小于400μm的界面结构具有良好的骨体孔隙结构成形性和较好的界面材料结合能力。该方法为复合材料支架仿生结构设计与制造一体化的研究提供新的评估与预测手段。     

骨组织工程用细胞支架生物材料的研究进展

概述了作为骨组织工程细胞支架修复和替换用的高分子生物材料、生物陶瓷材料、陶瓷/聚合物基复合材料和第三代生物活性复合材料的研究进展。指出模拟天然骨形成机制,可以制备出仿生径向梯度分布、生物活性、无机物增强相与可降解材料复合且多孔的细胞支架材料,将是未来骨组织工程用支架材料的发展趋势。     

PLLA/CPC复合支架增强结构设计及制备

为制备用于负重部位骨缺损修复的人工植入体,提出了一种复合增强结构人工骨设计及制备方案,该方案采用聚左旋乳酸支架(PLLA)为增强结构,以自凝固磷酸钙骨水泥(CPC)为复合填充材料,制备了复合增强结构人工骨。研究了PLLA的棒材力学性能、支架设计和制作及其不同增强结构形式对人工骨力学性能的影响。力学试验结果表明,所制作的人工骨有效提高了承载能力,并且该复合结构能有效弥补金属骨无法降解的缺陷。     

基于TPMS建模方法进行仿生骨支架结构设计

为了更好地拟合出人体骨细胞生存生长的多孔曲面环境,采用基于函数的极小三周期曲面(TPMS)建模方法,来进行仿生骨支架结构的设计。采用这种方法,能够通过调整函数的相关参数,实现对仿生骨支架孔径大小以及孔隙率大小的精准控制。选取了TPMS结构中的一种P曲面结构,通过与人体真实骨组织结构单元孔径大小以及孔隙率大小进行比对,选定了P曲面结构的参数值u,并确定了仿生骨支架合理的单元尺寸,最后通过有限元仿真软件对模型进行了力学分析及评估,结果表明,设计的支架结构具有更匹配人体骨结构的力学性能,对指导构建人工骨支架结构具有重要意义。     

碳纤维含量对TiB_2-TiN基复合陶瓷组织和性能的影响

在1700℃的高温下利用真空热压烧结技术,制备C_(sf)含量不同的TiB_2-TiN新型复合陶瓷刀具材料。研究了不同含量C_(sf)下的TiB_2-TiN新型复合陶瓷刀具材料微观组织和力学性能,结果表明:添加少量C_(sf)对TiB_2-TiN复合陶瓷有增强作用,然而当C_(sf)含量增加到一定量后,材料微观组织中的缺陷增多,抗弯强度、断裂韧度均呈现减小趋势,但是硬度却随着C_(sf)含量的增加一直减小;当C_(sf)含量为1.5wt%时,力学性能良好、微观组织的缺陷少,此时的抗弯强度为738±21MPa,断裂韧度为12.07±0.3MPa·m~(1/2),硬度为19±0.6GPa。     

短切碳纤维C_(sf)含量对TiC基复合陶瓷刀具材料微观组织及力学性能的影响

金属烧结剂选择Ni和Co,增强相选择短切碳纤维C_(sf),采用真空热压烧结技术,在1500°C下制备了短切碳纤维C_(sf)含量不同的TiC基复合陶瓷刀具材料。研究了C_(sf)的含量对TiC基复合陶瓷刀具材料微观组织和力学性能的影响,结果表明:加入C_(sf)后,复合陶瓷刀具材料断裂方式为穿晶断裂和沿晶断裂方式并存,在C_(sf)含量增加的过程中,TiC基复合陶瓷刀具材料的硬度逐步下降,抗弯强度和断裂韧度先变大后减小;当增加到2wt%C_(sf)时,获得了最佳的力学性能,硬度为14.32±0.16GPa,断裂韧度为8.70±0.15MPa·m~(1/2),抗弯强度为695.63±15.01MPa。     

基于骨组织微结构模型的仿生支架逆向设计

模拟人体骨组织结构,满足其几何相容性与生物适应性功能约束要求的多孔骨支架微观结构构建为组织工程中的关键问题。提出一种模拟人体骨组织多孔微观结构来构建仿生支架的逆向设计方法。利用Micro-CT扫描人体胫骨的微观结构,发现其孔的形态与椭球接近。为寻找人体骨结构的分布规律,利用椭圆最小二乘法拟合人体骨的Micro-CT图像,结果表明人体胫骨的微孔短径和长径的值分别分布在0.24mm和0.48mm附近。为使设计的多孔骨支架具有良好的生物和力学性能,将所得胫骨孔径参数创建椭球体,并通过UG二次开发技术将大量的椭球体相交形成仿生支架。研究所得的仿生支架采用人体骨结构参数,在生物和力学性能上与骨结构更为接近,对骨组织工程中的骨支架设计有一定的参考价值。     

组织工程骨支架微宏观模拟分析

应用沉积挤出快速成型技术制备组织工程骨支架过程中,复合生物材料之间相互作用的稳定性、喷头装置中复合凝胶的流动状态及制备工艺参数影响组织工程骨支架成型及成型后骨支架力学性能和孔隙结构。针对以上问题,应用分子动力学模拟软件Materials studio中经典力学工具Forcite对羟基磷灰石(HA)/聚乙烯醇(PVA)/丝素蛋白(SF)共混体系进行模拟,分析羟基磷灰石与生物复合凝胶聚乙烯醇/丝素蛋白相互作用后稳定性。结合三者混合材料特性,通过有限元模拟软件FLUENT分析复合生物材料的流动状态,依据流体分析结果,调整制备骨支架工艺参数。模拟结果表明,HA/PVA/SF三者混合材料具有良好粘结性及力学性能;有限元模拟计算出高粘度材料制备过程中流体状态分布。通过实验,结合流体分布状态,调整最佳制备参数,制备的骨支架具有良好的力学性能,混合生物材料成分基本未发生变化,表面微观孔隙能够达到生物因子驻留和营养物质交换的要求。     

立体空心血管网水凝胶支架的3D打印工艺研究

搭建同轴喷头打印系统,研究氯化铁溶液对由同轴针头打印出的藻酸盐水凝胶空心圆管的机械强度和成型结构的影响,建立3D打印优化工艺。将质量分数为2%~4%的海藻酸钠和质量分数为4%的氯化钙通过同轴针头打印出空心圆管。将质量分数为0.25%的雾化氯化铁溶液与空心圆管反应得到有氯化铁反应的空心圆管,力学试验发现经过与0.25%氯化铁反应的空心圆管的弹性模量(0.4677 MPa±0.279 MPa(2%海藻酸钠),2.0153 MPa±0.221 MPa(3%海藻酸钠),11.684 MPa±0.332 MPa(4%海藻酸钠))是无氯化铁溶液反应的空心圆管的弹性模量的5.4倍(2%),14.2倍(3%)和43.3倍(4%),其力学强度大大增强。机械强度增强的空心圆管完成了立体网络结构和螺旋结构的复杂类血管网,通过水凝胶溶液将其封装形成生物支架。灌流实验和细胞毒性试验表明该支架具有良好的生物相容性,可有效运输和灌注细胞培养液,满足了组织工程中制造大块软组织的工程化需求。     

骨支架多孔结构建模综述

3D打印技术的快速发展为复杂多孔骨支架的加工成型开创了条件,也使得组织工程支架研究工作重心从制造转向原型设计和高端个性定制。针对仿生骨支架复杂结构建模问题,重点介绍了造孔单元和功能梯度结构设计的研究现状,总结了现阶段仿生骨支架数字化设计中存在的问题,并展望了未来可能的研究方向。     

稀土强韧化陶瓷刀具材料的研制

研制出一种稀土钇强韧化Al2O3/Ti(C,N)新型陶瓷刀具材料,并对其力学性能和切削性能作了研究,表明稀土钇的适量添加能有效改善Al2O3/Ti(C,N)陶瓷刀具材料的力学性能,其抗变强度和断裂专访性分别达到1010MPa和6.1MPam^1/2。大量的切削实验表明,在切削淬硬45钢时,该刀具材料不仅具有良好的耐磨性能。而且具有较好的抗破损性能,其抗破损性能比相应不含稀土钇的Al2O3/Ti(C,N)陶瓷刀具材料高约20%。     

碳纳米管增强聚合物复合材料的界面脱黏及应力分布

碳纳米管和复合材料基体间的界面力学行为是影响复合材料宏观力学性能的重要因素,为此本文利用有限单元法对单壁碳纳米管增强聚合物复合材料的界面脱黏、切应力分布及拔出载荷进行了数值模拟。建立了一个轴对称三圆柱壳模型,引入ABAQUS中的Cohesive单元模拟了单壁碳纳米管和聚合物基体之间的界面层,分析了单壁碳纳米管的长细比、界面强度以及热残余应力等因素对碳纳米管与聚合物基体间的界面切应力以及拔出载荷的影响。模拟结果表明：当单壁碳纳米管的长度变化为50~100 nm、与基体之间的界面强度为50~100 MPa、环境温度变化为100℃ 时,碳纳米管的长细比、界面强度以及由于热失配所引起的残余应力对单壁碳纳米管与聚合物基体间的界面切应力以及拔出载荷有着显著的影响。     

尼龙帘线增强NR/SBR并用胶基磁敏橡胶的磁流变效应及其力学性能

由于可通过外加磁场来控制磁敏橡胶的刚度和强度,同时可解决磁流变液颗粒沉降、稳定性差的问题,因此磁敏橡胶成为国内外广泛关注的一种新型智能材料。制备了尼龙帘线增强型天然橡胶/丁苯橡胶(natural rubber/styrenebutadiene rubber,NR/SBR)并用胶基磁敏橡胶,采用Zwick/Roell电子拉力机和力磁耦合动态力学分析仪研究其静态力学性能和动态磁流变效应。结果表明,尼龙帘线的加入可以极大地提高磁敏橡胶的抗拉强度,同时也可提高磁敏橡胶的剪切模量和零场剪切储能模量;当加入三层帘线时,其抗拉强度可达到17.8 MPa,零场剪切储能模量为2.87 MPa;但随着尼龙帘线的增多,其磁流变效应则降低。     

Effects of manufacturing process and surface treatments on mechanical properties of PLA/SCF composites using extrusion printing

Short carbon fiber (SCF) reinforced polylactic acid (PLA) composites were fabricated by extrusion printing, and the effects of process parameters and surface treatments on the mechanical properties of composites were studied. Based on the rheological properties of composites and the extrusion process simulation, pure PLA specimens and PLA/SCF specimens were manufactured under different printing parameters. Three kinds of surface treatment were adopted to improve the mechanical properties. The experimental results show that SCF can effectively improve the tensile strength and bending strength, but the compressive strength decreased. The specimen had the best mechanical properties when the layer height was 0.1 mm and the nozzle diameter was 0.6 mm. The mechanical properties can be further improved by coupling agent coating method, and the compressive strength was even higher than that of pure PLA specimen. The research in this paper can provide a reference for the fabrication of thermoplastic composites with excellent mechanical properties by extrusion printing.

     

ZrO2陶瓷与钛合金非晶钎焊

由于陶瓷的线膨胀系数与金属的线膨胀系数相差很大,因此在通过焊接连接陶瓷与金属时,热作用势必会在接头区域会产生幅值较大的残余应力,进而降低接头的力学性能,严重时甚至会导致连接陶瓷接头的断裂。这使得陶瓷与金属的连接是一个广受关注但又未能得到很好解决的科学问题。采用非晶钎料实现ZrO2陶瓷与Ti-6Al-4V合金的钎焊连接,研究焊接工艺参数对接头的组织与性能的影响。结果表明接头界面组织结构为ZrO2陶瓷/Cu2Ti4O+(Ti,Zr)2Cu/TiO+Ti2O/CuTi2+(Ti,Zr)2Cu/ CuTi2/Ti-6Al-4V合金。钎焊温度、保温时间和冷却速度对界面组织结构有最大的影响,主要体现在反应层的厚度和脆性(Ti,Zr)2Cu相的变化。接头的剪切强度随钎焊温度、加热时间和冷却速度的增加而降低。最佳工艺参数为焊温度1 173 K,保温时间10 min,冷却速度5 K/min,其钎焊接头剪切强度可以达到165 MPa。     

Fabrication of porous beta-tricalcium phosphate with microchannel and customized geometry based on gel-casting and rapid prototyping

The tissue engineering scaffolds with three-dimensional porous structure are regarded to be beneficial to facilitate a sufficient supply of nutrients and enable cell ingrowth in bone reconstruction. However, the pores in scaffolds tend to be blocked by the cell ingrowth and result in a restraint of nutrient supply in the further side of the scaffold. An indirect approach of combining the rapid prototyping and gel-casting technique is introduced in this study to fabricate beta-tricalcium phosphate (beta-TCP) scaffolds which not only have interconnected porous structure, but also have a microchannel network inside. The scaffold was designed with customized geometry that matches the defect area, and a double-scale (micropores-microchannel) porous structure inside that is beneficial for cell ingrowth. The scaffolds fabricated have an open, uniform, and interconnected porous architecture with a pore size of 200-400 microm, and posses an internal channel network with a diameter of 600 microm. The porosity was controllable. The compressive yield strength was 4.5 MPa with a porosity of 70 per cent. X-ray diffraction analysis shows that these fabrication processes do not change the crystal structure and chemical composition of beta-TCP. With this technique, it was also possible to fabricate porous scaffolds with desired pore size, porosity, and microchannel, as well as customized geometries by other bioceramics.     

Effect of Trace Addition of Ceramic on Microstructure Development and Mechanical Properties of Selective Laser Melted AlSi10Mg Alloy

Selective laser melting(SLM) is an emerging additive manufacturing technology for fabricating aluminum alloys and aluminum matrix composites. Nevertheless, it remains unclear how to improve the properties of laser manufactured aluminum alloy by adding ceramic reinforcing particles. Here the effect of trace addition of TiB_2 ceramic(1% weight fraction) on microstructural and mechanical properties of SLM-produced AlSi10Mg composite parts was investigated. The densification level increased with increasing laser power and decreasing scan speed. A near fully dense composite part(99.37%) with smooth surface morphology and elevated inter-layer bonding was successfully obtained. A decrease of lattice plane distance was identified by X-ray di raction with the laser scan speed decreased, which implied that the crystal lattices were distorted due to the dissolution of Si and TiB_2 particles. A homogeneous composite microstructure with the distribution of surface-smoothened TiB_2 particles was present, and a small amount of Si particles precipitated at the interface between reinforcing particles and matrix. In contrast to the Al Si10 Mg alloy, the composites showed a stabilized microhardness distribution. A higher ultimate tensile strength of 380.0 MPa, yield strength of 250.4 MPa and elongation of 3.43% were obtained even with a trace amount of ceramic addition. The improvement of tensile properties can be attributed to multiple mechanisms including solid solution strengthening, load-bearing strengthening and dispersion strengthening. This research provides a theoretical basis for ceramic reinforced aluminum matrix composites by additive manufacturing.     

Functional graded scaffold of HDPE/HA prepared by selective laser sintering: microstructure and mechanical properties

This paper presents a study on the effect of hydroxyapatite (HA) content on the microstructure and mechanical properties of high-density polyethylene (HDPE)/HA composites and the fabrication of functional graded scaffold of HDPE/HA by selective laser sintering (SLS). The microstructure of the sintered composite scaffolds had interconnected pores with diameters of 30–180 μm and porosity of 45–48 %. The HDPE/HA composite scaffolds had a flexural modulus of 36–161 MPa and ultimate strength of 4.5–33 MPa. The maximum loss modulus peak tended toward lower temperature values for HDPE/HA composites with 10 and 20 % of HA content, indicating that the α_χ relaxation was slightly affected by higher quantities of HA. The HA particles reinforced the matrix and minimized the plastic and definitive deformation under the test conditions. HDPE/HA functional graded scaffold fabricated using SLS with controlled microstructure and properties showed considerable potential for biomedical applications, being suitable for bone and cartilage tissue engineering.     

铜铋合金与ZrO2陶瓷扩散焊接头的组织与剪切强度

在1.3Pa的真空环境下,用扩散焊接法进行了Cu-x%Bi合金(x=0,0.5,1.0,2.0)与ZrO2陶瓷的连接,并采用扫描电镜、电子探针及剪切试验机等研究了铜铋合金与ZrO2陶瓷扩散焊接头的组织及剪切强度。结果表明:在焊接压力作用下挤入接合界面的铋,在焊接后部分残留在界面上,对焊接热应力有缓释作用,可提高接头的剪切强度;当接头的使用温度高于373K后,由于界面上铋的软化,接头的剪切强度急剧下降,难以在高温环境中使用。     

气氛对AZ31B镁合金扩散连接接头性能的影响

针对AZ31B镁合金扩散连接中的气氛保护难题,利用VDW-15型扩散焊设备对厚度为1．0mm的AZ31B镁合金薄板进行了在不同连接气氛条件下的扩散连接。分析了不同气氛下试样的表面状态,对连接接头进行了剪切强度、显微硬度等力学性能测试,利用金相显微镜、扫描电镜对不同气氛下的扩散连接接头显微组织、断口形貌进行了分析,试验结果表明,在扩散连接过程中采用抽真空至4．0×10^-3Pa,再回充高纯氩气保护的方法得到了性能较好的接头,试样表面光洁,剪切强度为39．5MPa,断口分析表明其为脆性断裂。