纤维增强热固性复合材料构件的固化变形研究进展

热固性复合材料的固化是一个热性能、化学性能和力学性能同时发生变化的复杂过程,也是固化变形和残余应力产生的过程。引起复合材料变形的因素主要包括构件的结构形式、树脂含量、铺层方式、基体树脂的特性、固化工艺参数及模具因素等。其中,复合材料固化过程中树脂的热收缩、化学收缩以及模具材料与复合材料间热膨胀系数的差异是引起复合材料发生固化变形的根本原因。     

复合材料制品的固化变形研究

热固性树脂基复合材料在热压罐成型过程中,由于模具的约束作用,工件内部会产生残余应力,进而引起工件回弹变形和翘曲变形。本文以层合板为例,分析固化工艺、铺层方式等因素对固化变形的影响。     

注塑件脱模后翘曲变形数值分析

分析了注塑过程中残余应力产生的原因,并通过数值模拟分析了热残余应力对注塑件翘曲变形的影响,研究了塑件上下表面温差、制品结构、厚度以及脱模后塑件冷却速度等因素对翘曲变形的影响,指出了脱模后塑件上下表面的温差和塑件厚度是产生翘曲变形的主要因素。     

基于Moldflow Insight2010的降低制品残余应力分析

注塑制品的残余应力影响制品的形状、表面质量及使用性能.在分析残余应力产生的机理和原因的基础上,应用软件模拟实验方法,介绍了降低残余应力的方法,结果发现冷却方式与熔体温度对残余应力的影响很大,其次是模具温度、保压压力和保压时间的影响,程度依次递减.得出的结论对工程实际应用有一定的指导意义.     

汽车A柱下饰板注射成型工艺仿真分析

采用正交试验和Moldflow数值模拟相结合的方法,对汽车A柱下饰板的注射成型过程进行了分析,研究了模具温度、熔体温度、注射时间和保压压力等工艺参数对残余应力和翘曲变形的影响。通过极差分析得到,熔体温度对翘曲变形影响最大,保压压力对残余应力影响最大,最佳工艺参数组合为模具温度40 ℃,熔体温度205 ℃,注射时间5 s,保压压力45 MPa;通过仿真分析与实际成型方案进行比较,汽车A柱下饰板的翘曲变形由3.847 mm降为3.121 mm,残余应力由66.95 MPa降为65.21 MPa。     

薄壁塑件注射压缩成型工艺的模拟分析

基于正交分析法和单因素分析法,用Moldflow软件数值模拟注射压缩成型中不同工艺条件对薄壁制品残余应力的影响.计算的残余应力沿厚度方向的分布表明:薄壁制品残余应力主要为流动诱导残余应力.模具温度与压缩距离对制品残余应力影响显著,模具温度越高,压缩距离越大,制品残余应力越小;其他工艺参数对残余应力均有不同程度的影响.     

微孔塑料注射成型制品体积收缩与翘曲变形数值分析

采用Moldflow软件，通过微孔注射成型过程的数值模拟，系统研究了熔体注射温度、模具温度对其体积收缩、翘曲变形和残余应力的影响规律，并基于流变学理论，揭示了其影响机理。研究结果表明，随着熔体注射温度和模具温度增加，微孔注射制品翘曲变形和残余应力均增加，成型制品的体积收缩随着熔体注射温度升高而增加，而随着模具温度升高而减小。本研究为微孔注射成型工艺和模具的设计提供理论指导。     

大型硫酸储罐焊接变形矫正与修复

介绍了万吨级硫酸储罐的设计参数、结构、制造过程与制造要求。描述了硫酸储罐底板上凸变形、壁板外凸变形的现象,经分析认为造成的原因是制造组装残余应力和焊接残余应力所导致,说明了残余应力和变形的危害,从扇形底板上凸变形矫正和壁板开孔外凸变形矫正两个方面详述焊接变形的矫正与修复,提出降低焊接残余应力及焊接变形的措施与建议。     

轮胎阶梯式直压硫化内模具的结构强度研究

利用Abaqus软件对225/40R18轮胎阶梯式直压硫化内模具（简称内模具）的结构强度进行研究。结果表明：内模具在4.6 MPa的硫化压力下,最大应力出现在宽鼓瓦楔块滑块上,远小于滑块材料铍青铜的许用应力;内模具机构的最大变形位移为0.140 7 mm,其变形为弹性变形,对机构运动和轮胎质量不会产生影响;内模具的各零件的结构强度均满足设计要求。该研究可为阶梯式直压硫化轮胎的工业化生产提供参考。     

储罐焊接中防止变形的一些建议

通过对焊接施工产生变形的原因分析研究,找出在工程质量控制中,严格控制人员、机械设备、工程材料及施工方法,并且着重探讨施工方法及其注意事项,最终确立合适的焊接顺序。因为焊接顺序对焊接残余应力和变形的产生及分布影响最大,采取合理的施焊顺序,可以有效的减小焊接残余应力和防止焊接残余变形。     

关于自增强残余应力松弛规律的研究

以高压聚乙烯量式反应器为侧．对自增强废余应力松弛规律进行研究,分析自增强残余应力的松弛特点、原因和机理，着重研完自增强废余应力松弛的影响因素茛其对友余应力的影响情况。     

Impact strengthening of 3Y-TZP dental ceramic root posts

3Y-TZP ceramics are commonly used in restorative dentistry for fixed partial dentures, implants, abutments and root posts. The stress-induced transformation-toughening mechanism leads to improved mechanical properties advocating 3Y-TZP to be ground or sandblasted for better clinical performance. Such invasive mechanical treatments facilitate the additional surface strengthening as a result of the residual compressive stresses, but the exact origin is not completely understood. This study evaluated the effect of continuous impacting between 3Y-TZP root posts during 500 -h-long shaking on the extent of (sub)surface microstructural changes affecting the fracture strength. With an increase of the shaking time the surface roughness decreased, where the grains were flattened and partially spalled. The observed 6-micrometre-thick altered subsurface region containing compressive residual stresses contributed to a systematic increase in the forces of fracture within the sample population; however, only for those containing the surface type of critical flaws that were in the form of mould imprints.     

关于自增强残余应力松弛规律的研究

以高压聚乙烯管式反应器为例,对自增强残余应力松弛规律进行研究,分析自增强废余应力的松弛特点、原因和机理,着重研究自增强残余应力松弛的影响因素及其对发余应力的影响情况.     

薄壁球壳焊缝的应力与应变

依据球壳轴对称弯曲理论,导出了球壳赤道圆上对接焊缝残余应力和变形的定量解答。讨论了几何尺寸 (R、t)及焊接因素(σ0,b)对残余应力与变形的影响。     

Residual orientation in injection‐moulded plaques of atactic‐polystyrene I: The effect of processing conditions

Injection moulded polymer articles often have residual macromolecular or crystalline orientation which can have a significant impact on the optical and mechanical properties of the moulded article. Small angle neutron scattering (SANS) was used to measure the molecular shape and orientation of deuterated blends of injection moulded polystyrene. For ～1‐mm‐thick mouldings of uniform rectangular cross‐section, the eccentricity in the SANS pattern gave a direct measure of the residual molecular orientation over the length scale ～100–1,500 Å. The residual orientation was found to vary significantly with injection moulding conditions with comparative residual orientation decreasing with decreasing mould fill‐time, and increasing with mould thickness and moulding temperatures. The orientation was found to be a minimum in the centre of the mould and highest near the surface and the average orientation at a particular position in the mould was found to be strongly correlated with the volume of material deposited as a solid skin layer during injection moulding. POLYM. ENG. SCI., 58:1322–1331, 2018. © 2017 Society of Plastics Engineers     

海信空调风门叶片的翘曲变形研究

采用有限元方法研究了温度场、压力场对注塑件残余应力及翘曲变形的影响，重点讨论注塑件的温度场、压力场的计算，以及热塑性小变形理论下的注塑件翘曲变形计算。对影响薄壳塑件翘曲变形的因素（如模具温度、熔体温度、注射速率、保压压力等）进行分析，提出翘曲产生的原因及相应的改进措施。     

In situ monitoring of residual strain development during composite cure

Internal (residual) stresses build up in a thermosetting composite as the matrix shrinks during cure, and again as the composite is cooled to ambient from its elevated processing temperature. These stresses can be significant enough to distort the dimensions and shape of a cured part as well as initiate damage in off‐axis plies, either during fabrication or under the application of relatively low mechanical loads. The magnitude of these stresses depends on a number of factors including constituent anisotropy, volume fraction and thermal expansion, ply orientation, process cycle, and matrix cure chemistry. In this study, embedded strain gauges were employed to follow, in situ, the buildup of residual strains in carbon fiber‐reinforced laminates during cure. The data were compared to those from volumetric dilatometer studies to ascertain the fraction of resin shrinkage that contributed to residual stress buildup during cure. Based on earlier studies with single‐fiber model composites, the process cycle in each case was then varied to determine if the cycles optimized to minimize residual stresses for isolated fibers in an infinite matrix were applicable to the reduction of residual stresses in conventional multifiber composites. The results of these studies are reported here.     

Crack Stability and T-Curves Due to Macroscopic Residual Compressive Stress Profiles

Stabilization of the fracture process and resistance to strength degradation have been observed for materials with increasing T -curves. In this study, the possibility of using residual compressive stresses to induce crack stabilization is examined theoretically. Nonmonotonic forms for the residual compressive stress profiles are assumed. The stress intensity factors for linear through-the-thickness cracks subjected to these profiles are derived. The stress intensity factors are then used to construct the T -curves for the stress profiles considered. It is demonstrated that the presence of these T -curves leads to crack stability under the action of applied tensile stresses, and to strength insensitivity to the initial flaw size. The effects of additional localized stress fields (similar to those produced by indentation) on crack growth in these materials are also considered. In this case, the strength is found to be relatively insensitive to the magnitude of the localized loading. It is therefore concluded that residual stresses can be used to improve mechanical reliability in ways which are usually associated with microstructural toughening mechanisms.     

金属基烤瓷牙冠残余应力产生的原因与控制方法

详细分析了金属基烤瓷牙冠残余应力产生的原因，认为金属与烤瓷热膨胀系数不匹配，制备工艺不合理以及金属与烤瓷结合欠佳等是产生残余应力和导致烤瓷破坏的主要原因，并对如何控制残余应力，关少烤瓷开裂和肃落进行了论述。