烧结金刚石套料钻钻削凯芙拉纤维增强复合材料的研究

介绍凯芙拉纤维增强聚合物基复合材料的结构和性能特点,针对复合材料在钻孔加工过程中产生各种加工缺陷的原因,采用烧结金刚石套料钻和专用的工艺装置进行加工试验,分析加工机理,给出合适的工艺参数,为加工该类纤维复合材料提供一条新的途径,具有实用和推广价值。     

激光选区烧结超高分子量聚乙烯工艺及性能

研究了激光选区烧结(SLS)成型工艺中不同工艺参数以及后续热处理工艺对超高分子量聚乙烯(UHMWPE)材料成型性能的影响。通过调整扫描间距、激光功率、扫描速度等不同工艺参数,描述了SLS成型UHMWPE零件的致密度、拉伸强度以及断裂伸长率,并对热处理前后的SLS成型UHMWPE零件的力学性能进行了比较。结果显示,致密度、拉伸强度、断裂伸长率总体上与激光功率呈正相关关系,与扫描间距、扫描速度呈负相关关系。经热处理后,SLS成型UHMWPE零件的力学性能有明显提高,致密度达到95.12%,抗拉强度达到24.08 MPa,断裂伸长率达到334.82 MPa。实验结果表明:SLS成型UHMWPE零件与模塑成型UHMWPE零件性能尚有差距,仅优化成型工艺不足以得到理想性能,但经热处理后,零件性能基本满足使用要求。     

Fabrication of porous bioactive structures using the selective laser sintering technique

Hydroxyapatite, a ceramic with which natural bone inherently bonds, has been incorporated into a polymer matrix to enhance the bioactivity of implant materials. In order to manufacture custom-made bioactive implants rapidly, selective laser sintering has been investigated to fabricate hydroxyapatite and polyamide composites and their properties investigated. One objective of this research was to identify the maximum hydroxyapatite content that could be incorporated into the matrix, which was sintered at various parameters. The study focused on investigating the control of porosity and pore size of the matrix by manipulating the selective laser sintering parameters of the laser power and laser scan speed. The interception method was used to analyse the internal porous morphology of the matrices which were cross-sectioned through the vertical plane. Most notably, all structures built demonstrated interconnection and penetration throughout the matrix. Liquid displacement was also used to analyse the porosity of the matrices. The laser power showed a negative relationship between porosity and variation in parameter values until a critical power value was reached. However, the same relationship for laser scan speed matrices was inconsistent. The effects of the laser power and laser scanning speed on the features of porous structures that could influence cell spreading, proliferation, and bone regeneration are presented.     

激光选区烧结及其在精密制造业中的应用

研究了快速、精确制造金属模具的方法,提出利用激光选区烧结(SLS)技术来快速制造高精度陶瓷型精密铸造用母模.首先,采用正交试验法研究了激光选区烧结工艺参数对制件精度的影响,确定了最佳激光烧结工艺.在此基础上利用浸水起模法替代传统的起模喷烧工艺对陶瓷型精密铸造工艺进行改进.结果表明,选定激光烧结工艺参数为激光功率25 W,扫描速度2.0 m/s,扫描间距0.19 mm,分层厚度0.25 mm时,试样尺寸收缩率最低可达2％.采用陶瓷型浸水起模法起模容易,起模后陶瓷型表面光洁,在200℃焙烧温度下抗弯强度较高,为0.361 MPa.这些结果表明,利用SLS技术能够快速、准确地制造出陶瓷型精密铸造所需母模.     

颗粒增强金属基复合材料的制备进展

介绍颗粒增强金属基复合材料的常用制备工艺,分析各种制备方法的优缺点;论述对颗粒增强金属基复合材料制备技术研究的难点,并展望金属基复合材料的发展。     

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.     

Fretting behaviors of hot-pressed electrospun hydroxyapatite/poly(dl-lactide) fibrous composites as potential orthopedic implants

In situ grown composite fibers of hydroxyapatite (HA) and poly(dl-lactide) with uniaxial distribution were deposited layer-by-layer followed by hot pressing to obtain fibrous composites. The tribological profiles were clarified at low amplitude oscillatory motion as potential orthopedic implants. The inoculation of HA nanoparticles into fibrous composites lowered the coefficients of friction (COFs) and wear rates, and the hardness of HA layers and rolling effect of HA particles further improved the wear resistance. The COFs and wear rates were significantly lower when fretting along the fiber orientation than those when the slide direction was perpendicular to the fiber alignment.     

A macroscale FEM-based approach for selective laser sintering of thermoplastics

A numerical approach to model the selective laser sintering (SLS) of polypropylene is proposed. A 3D thermal model was developed and thus enables the prediction of the temperature fields and the extension of the sintered area in the powder bed taking into account the phase change during multiple laser passes. Powder–liquid, liquid–solid and solid–liquid phase changes were modelled during the SLS and the subsequent cooling processes. Then, a 3D thermomechanically coupled model was set up based on the temperature results of the thermal model in order to predict the distortion of the produced parts after cooling down. Different pre-heating temperatures were considered, highlighting their influence on the final part properties.     

Chitosan-based hyaluronan hybrid polymer fibre scaffold for ligament and tendon tissue engineering

To establish medical use of tissue engineering technology for ligament and tendon injuries, a scaffold was developed which has sufficient ability for cell growth, cell differentiation, and mechanical properties. The scaffold made from chitosan and 0.1 per cent hyaluronic acid has adequate biodegradability and biocompatibility. An animal experiment showed that the scaffold has less toxicity and less inflammation induction. Furthermore, in-vivo animal experiments showed that the mechanical properties of the engineered ligament or tendon had the possibility to stabilize the joint. It was shown that newly developed hybrid-polymer fibre scaffold has feasibility for joint tissue engineering.     

Investigation of laser and process parameters for Selective Laser Erosion

The process of Selective Laser Erosion (SLE) was investigated to study the effects of different process and laser parameters on the process outputs such as surface quality and erosion rate. The SLE process is a direct method to remove material in a layer-by-layer fashion due to high energy densities provided by the laser beam. In addition to its direct use as a subtractive manufacturing method, SLE may be used in combination with layer-additive techniques such as Selective Laser Melting (SLM). Such combination mainly makes sense when both processes can be performed with the same laser. However, one of the major problems involved in SLE process is the high number of the laser and process parameters (laser power, pulse frequency, scan speed, scan spacing, ambient atmosphere, etc.) and the complexity of the relations between them which has not yet been investigated completely.This paper presents an overview of the laser erosion process with nano-second Nd:YAG laser pulses and the results of several single-factor experiments that were carried out to determine the influence of the major parameters on the depth of erosion per layer and surface roughness. Additionally, the relations between the parameters are studied to investigate the interactions between them. The results from single-factor experiments showed that some relations were highly governed by the power intensity of the laser beam and also that cross interactions between the parameters play an important role on the output characteristics. The paper explains how multiple parameters (spot size, pulse frequency, scan speed, scan spacing) can be combined to define two indirectly controlled geometrical parameters, namely the scan and pulse overlap factors. Those two parameters allow calculating the number of hits of the laser beam on a same location on the workpiece possible which is the first step in physical modeling the topography of the surface left behind.     

滚挤压加工对颗粒增强铁基复合材料表面硬度的影响

研究滚挤压加工工艺对颗粒增强铁基复合材料表面硬度的影响,结果表明,滚挤压加工工艺在一定程度上改善了颗粒增强铁基复合材料的表面硬度.随滚压力及滚挤压次数的增加,表面显微硬度随之上升,而随进给量的增加,表面显微硬度变化的幅度减小.通过试验得出加工这种复合材料合理的工艺参数范围.     

Mechanical properties of inorganic particle reinforced epoxy composites for gas insulated switchgear

In this study, the particle reinforced epoxy composite with alumina and silica was considered to insulation material for the gas insulated switchgears (GIS     

选择性激光烧结激光能量密度与温度补偿规律研究

选择性激光烧结（SLS）成型预热温度从成型缸中间到缸壁呈降低趋势,由于预热温度不均匀,导致SLS成型件密度不均匀。针对这一问题,通过增加激光能量密度对预热温度不足进行了补偿。通过试验建立了激光能量密度差△E与预热温差△T的经验公式,并比较了温度补偿前后烧结件的机械强度。实验结果表明,通过增加激光能量密度对预热温度不足进行补偿,提高了产品机械强度。     

Wear characteristics of some internally lubricated and reinforced engineering polymer composites

An interesting characteristic of abrasion is the dependence of the wear rate on the particle size of the abrasive grits used to lubricate the abrasive papers. Three types of polymers, PTFE, PA, PI, several of their composites, and three metals were selected for studying the effect of particle size on wear rate. The pins were abraded against Sic abrasive papers of various mesh sizes under constant loading in multi-pass conditions. For some of the polymers and their composites (PA and PEI) the size effect on wear rate was similar to that for the metals. Beyond a critical particle size, no increase in wear was found with increasing particle size. On the other hand, PTFE, PI, and their composites showed the opposite effect. SEM and EDAX were used to investigate the related mechanisms.     

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。     

Optimizing process parameters for selective laser sintering based on neural network and genetic algorithm

Selective laser sintering (SLS) is an attractive rapid prototyping (RP) technology capable of manufacturing parts from a variety of materials. However, the wider application of SLS has been limited, due to their accuracy. This paper presents an optimal method to determine the best processing parameter for SLS by minimizing the shrinkage. According to the nonlinear and multitudinous processing parameter feature of SLS, the theory and the algorithms of the neural network are applied for studying SLS process parameters. The process is modeled and described by neural network based on experiment. Moreover, the optimum process parameters, such as layer thickness, hatch spacing, laser power, scanning speed, work surroundings temperature, interval time, and scanning mode are obtained by adopting the genetic algorithm based on the neural network model. The optimum process parameters will be benefit for RP users in creating RP parts with a higher level of accuracy.     

用于SLS快速成形制造中振镜式激光扫描系统的关键技术

针对选择性激光烧结快速成形制造的需求，探讨并深入研究了振镜式激光扫描系统的组成，成形过程中线性扫描、图形畸变的校正、扫描系统机械滞后性的补偿、激光功率与扫描速度的匹配及成形精度等关键技术问题。