混杂纤维增韧水泥基复合材料的静动态弯拉性能

为了掌握钢纤维-聚乙烯纤维(PE纤维)混杂对水泥基材料静动态弯拉性能的影响规律,通过三点弯拉试验和落锤冲击试验方法,研究了钢-PE纤维混杂(掺量保持体积分数2.0%不变)增韧水泥基复合材料(HFTCC)的静动态弯拉性能,分析了钢纤维与PE纤维的混杂效应以及相应的增韧机理。结果表明：HFTCC静态弯拉性能与钢-PE纤维中PE纤维掺量正相关,而动态弯拉性能与钢纤维掺量表现出较强的正相关。1.5%(体积分数) PE纤维与0.5%钢纤维混杂表现出最佳的静态弯拉峰值应力;1.5%钢纤维0.5%PE纤维表现出最佳的动态弯拉能量吸收。在静态弯拉下,钢-PE混杂纤维相较于2.0%钢纤维对HFTCC峰值强度及能量吸收提升幅度分别为26.5%～31.7%与14.8%～56.8%;HFTCC的动态强度增长因子(DIF)与能量吸收表现出明显的应变率效应。钢纤维和PE纤维适当混杂可对HFTCC发挥较好的协同增强增韧效应,从而有效提升HFTCC的静动态弯拉性能。     

纤维增强磷石膏轴心受拉应力-应变曲线研究

为研究纤维增强磷石膏的受拉应力-应变曲线，将磷石膏粉、水泥、纤维的质量比设定为90%、10%及0.2%,以水灰比(0.7、0.8、0.9)为变化参数，制作了12个棱柱体试块。通过轴向单调拉伸试验，分析了纤维增强磷石膏的受拉应力-应变曲线、抗拉强度、峰值应变等力学指标。对归一化曲线进行拟合，给出了应力-应变曲线的数学表达式。研究表明，受拉应力-应变曲线呈非线性变化，且水灰比越低，曲线越陡峭；当水灰比从0.7增加至0.8及0.9时，轴心抗拉强度分别降低了11.4%及34.3%;峰值拉应变受水灰比影响较小，应变测量值位于31.5με～54.8με区间。     

超载作用下沥青路面的力学响应

本文从理论上探讨了沥青路面在车辆超载情况下的力学响应变化,包括路表弯沉值,基层底弯拉应力和基层顶面压应变。路面结构选用半刚性基层路面和柔性基层路面,荷载采用四组不同的压力。结果表明,路表弯沉值、层底弯拉应力和路基压应变随着轴载的增加而增加,并且超载会导致对沥青路面早期损坏的严重影响。     

横向剪应变对正交异性板弯扭耦合效应影响的数值分析

本文给出了层合板位移增量型的平衡微分方程。定量地估计了横发变形对四边铰支的正交异性板弯扭耦合效应的影响。结果表明：四边铰支的正交异性层合板，当其长厚比小于３０时，横发变形对其位移和应力的影响是不容忽略。     

PA6材料拉-扭组合的力学特征及屈服准则的试验研究

为了研究PA6在拉-扭组合作用下的力学特征、屈服准则及强度条件,利用电子拉-扭试验机对PA6材料进行了6种加载速率下的拉-扭组合变形试验,得到了相应的正应力与正应变、切应力与切应变的关系曲线;通过试验验证了Mises屈服准则可作为PA6材料的拉-扭屈服准则;基于最小二乘法建立Mises屈服准则中应力偏张量的第二不变量关于PA材料密度、声波速率、拉伸加载速率、扭转加载速率的拟合模型。由该拟合模型,可以不做加载破坏试验,即可建立PA6的拉-扭屈服准则,得到拉-扭屈服时的相当应力,并通过该屈服准则建立强度条件,可进行相应的PA6拉-扭强度计算。     

汽车厚板冲压件横梁的工艺分析和模具结构

通过特定零件成形过程的受力状态、应力应变状态分析,介绍了汽车厚板冲压件——横梁通过拉弯成形的冲压成形工艺,并结合CAE分析和实际模具调整为依据．分别阐述了成形模和剖切模的模具结构与工作要点。经生产验证,该工艺合理,模具结构紧凑、制造简便、成本低、操作方便、生产效率高,为制造类似零件提供参考。     

低渗油藏流固耦合效应及其应用

以渤南油田义37块沙三^8低渗油层为例，研究了低渗透油藏流固耦合效应及其对低渗透油藏开发的影响。低渗油藏变形包括弹性应变和塑性应变两种机理，随着有效压力逐渐增加，岩样渗透率逐步下降，岩石从弹性应变逐渐转变为塑性应变，二者之间存在转换机制；本文通过对实验结果的分析，建立了低渗储层渗透率随应力变化模型，分析了流固耦合对渤南低渗透油田开发的影响，为低渗透油藏开发方案调整提供依据。     

黄磷脱砷中文丘里反应器的流固耦合研究

基于计算流体力学和流固耦合原理,利用FLUENT的Realizable k-ε湍流模型,计算得到文丘里反应器内部流场分布,通过ANSYS Workbench中的流固耦合技术,将流场分析的结果数据传递到Static Structure中进行结构静力分析,从而得到流场分布、喷嘴所受压力、喷嘴变形、应力应变等分析结果。结果显示,在特定工作压力条件下,文丘里反应器的扩散管在工作中有向吸入管相反方向变形的趋势;在整个结构中,最大应力和应变值均集中在喷嘴内流道中;由于高速流体的射流作用,喷嘴出口附近结构主要承受拉应力的作用。由于计算得到的应力和应变数值均处于较低水平,因此结构能够满足工况的要求。     

0°和90°缠绕角圆和非圆截面梁在拉弯载荷下的位移计算

本文提出一种0°和90°缠绕角圆和非圆截面梁在拉弯载荷作用下的变形计算方法。本法将圆或非圆截面梁化分为有限个梁元进行位移、应变、应力分析，通过坐标转换，将各梁元的位移和载荷在梁上进行整合，从而得出0°和90°缠绕角圆或非圆截面梁在拉弯载荷作用下的分析模型。文中将理论计算结果与有限元数值计算结果进行对比，理论计算结果与数值实验结果有较好的一致性。结果说明，本文提出的计算方法可应用于0°和90°缠绕角圆和非圆截面梁在拉弯载荷作用下的分析计算。     

混杂合成纤维混凝土单轴抗拉力学特性与本构关系

根据混杂纤维增强原理,采用高弹模聚乙烯纤维和低弹模聚丙烯粗合成纤维制备出具有优异变形性能的混杂纤维混凝土,采用单轴拉伸试验对其单轴受力特性进行了分析,并根据测试结果建立了单轴抗拉本构关系模型.结果表明,单轴受拉应力-应变曲线可以划分为弹性阶段、应变硬化阶段和破坏阶段三个阶段;在受拉过程中出现了多缝开裂现象,微细裂缝的扩展较为曲折,在开裂过程中吸收了大量的能量,导致变形能力大幅提升;掺入硅灰后使得界面过渡区性能改善,从而导致极限抗拉强度和拉应变的增大;纤维掺量过大时不能均匀分散,结团现象出现,极限拉应变反而下降;所建立的单轴受拉分段本构关系模型能够较好的反映应力-应变曲线的发展趋势,所推荐的模型参数计算公式具有较高的准确性.     

Molded geometry and viscoelastic behavior of film insert molded parts

Virgin injection‐molded tensile specimens without any inserted film and four kinds of film insert molded (FIM) tensile specimens were prepared. They were annealed at 80°C to investigate the effect of residual stresses and thermal shrinkage of the inserted film on thermal deformation of tensile specimens. The FIM specimens with the unannealed film were bent after ejection in such a way that the film side was protruded and the warpage was reversed gradually during annealing and the film side was intruded. Warpage of the FIM specimen with the film annealed at 80°C for 20 days was not reversed during annealing. Processing of the FIM specimens have been modeled numerically to predict thermoviscoelastic deformation of the part and to understand the warpage reversal phenomenon (WRP). Nonisothermal three‐dimensional flow analysis was carried out for filling, packing, and cooling stages. The flow analysis results were transported to a finite element stress analysis program for prediction of deformation of the FIM part. The WRP was caused by the combined effect of thermal shrinkage of the inserted film and relaxation of residual stresses in the FIM specimen during annealing. It is expected that this study will contribute towards the improvement of the FIM product quality and prevention of large viscoelastic deformation of the molded part. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

微孔薄膜挤出成型数值模拟

利用Unigraphics NX(简称UG)软件设计了8孔微孔薄膜挤出模,并对挤出模成型段及挤出物部分进行了CAE模拟,利用参数渐变法研究了不同拉伸应力下挤出物外形及横截面形状尺寸的变化。结果表明,随着拉伸应力的增大,挤出物横截面尺寸越来越小;气孔由圆形变为菱形、椭圆形;挤出物表面具有明显的波纹特征。     

用有限元法研究短纤维／橡胶复合材料内应力传递

采用有限元法对短纤维／橡胶复全材料内应力传递和分配规律进行了初步探讨。结果表明：纤维末端的界面剪切应力和纤维中部的拉伸应力均最大，纤维末端仍传递一定的拉伸应力；纤维体积分数越大，纤维末端端应力集中越严重；纤维长径比越大，纤维上的最大拉伸 力也越大，但增幅越于平缓；纤维模量增加，纤维上的拉伸应力集中也增加，但增减缓，基南模量增加，界面剪切应力集中和纤维拉伸应力集中均下降，但剪切应力和拉伸应力的红色     

Characterisation of mechanical properties of thin polymer films using a bi-axial tension based on blow-up test

Abstract

Blow-up tests were carried out to evaluate mechanical properties of the thin Nylon film used as bagging films. A new method for calculating bi-axial stress and strain of the thin film in blow-up tests was developed based on the theory of membrane with large strain solutions. The bi-axial tensile elastic modulus, Poisson's ratio, yield strength, fracture stress and bi-axial stress–strain relationship of the thin Nylon film were obtained. Meanwhile, uni-axial tensile tests were conducted and the results were compared with those from blow-up tests. For the Richmond HS-8171 thin Nylon film studied, the bi-axial tensile elastic modulus was slightly more than 2 times greater than the uni-axial tensile elastic modulus. The yield strength was the same for both bi-axial and uni-axial tension. The bi-axial fracture stress was about one-third greater than the uni-axial one, while the bi-axial failure strain was about two-thirds greater than the uni-axial counterpart.     

Intrinsic stress evolution in diamond films prepared in a CH4H2NH3 hot filament chemical vapor deposition system

The intrinsic stress in diamond films prepared in a CH₄H₂NH₃ hot filament chemical vapor deposition system has been investigated by the substrate curvature technique as a function of film thickness (2.2–50 μm) and ammonia concentration (0–1.4%). Our results indicated that the film stress changed from compressive to tensile with the increase of film thickness and diamond quality at a constant ammonia concentration of 0.5%. The existence of a non-diamond phase was found to be beneficial to the relaxation of intrinsic tensile stress in the films. The intrinsic stress in diamond films was tensile at an ammonia concentration from 0 to 1.4%, while the maximum tensile stress existed at 0.75% NH₃. The possible origin of intrinsic tensile stress was discussed.     

Film insert molding as a novel weld‐line inhibition and strengthening technique

Specimens with weld lines were produced via conventional and film insert molding techniques using two types of materials as the substrate resin, i.e. a polycarbonate/acrylonitrile‐butadiene‐styrene (PC/ABS) blend and glass fiber‐filled polycarbonate (PC‐gf). The formation and morphology of the weld line region was assessed with and without the presence of 0.5‐mm‐thick PC film inserts. The weld line formation and characteristics were found to be dependent on the extent of interaction between the injected resin and the mold surface or the film insert. Better interfacial interaction between the substrate and film led to the distortion of the weld line orientation, which significantly enhanced the mechanical properties of the weld line. The incorporation of glass fibers into the substrate resin would usually reduce the resistance of the weld line towards tensile, flexural and impact loadings. However, with the attachment of film inserts, the mechanical properties of the weld line region have significantly improved, even with the presence of rigid fibers. Upon examination of tensile and impact fracture surfaces of film insert specimens, a unique orientation of fibers across the weld line (parallel to the flow direction and perpendicular to the weld line) could be observed at regions directly under the film. The combination of favorable properties from the unique fiber orientation and distortion of the weld line, as well as the ability of the film to effectively dissipate forces towards a larger area, have synergistically contributed towards the mechanical property enhancement of the weld line region in film insert moldings. POLYM. ENG. SCI., 2008. © 2008 Society of Plastics Engineers     

缓冲包装材料静载机械特性影响的试验研究

通过对蜜瓜在不同条件下采用缓冲材料包装前后的静载压缩试验以及缓冲材料的拉伸试验,分别获得了蜜瓜裸果及缓冲包装后的压缩特性及缓冲材料的拉伸特性。试验结果表明,采用缓冲材料包装后的果实能明显改善受压过程中的变形情况;缓冲材料自身性能与被包装果实的抗压性有关,缓冲材料EPS的纵向拉伸强度高于EPE,装有EPS薄膜包装箱样品的最大屈服极限在装有EPE薄膜包装箱的基础上增加了20%,并且EPS薄膜形变后回弹性较好。试验结论对防止和减缓蜜瓜在储藏、运输和销售中由于挤压、碰撞、跌落而造成的损伤有一定指导意义,同时为缓冲包装设计提供了一定的理论依据。     

Mechanical properties of an aromatic polyamide-imide composite film reinforced with an aromatic polyamide fiber cloth at high temperature

An aromatic polyamide-imide (PAI) film was reinforced with a plain cloth of aromatic polyamide fiber (Du Pont, Kevlar 49). The mechanical properties of the composite film were investigated by examination of the temperature dependencies of tensile dynamic mechanical properties, stress relaxation, and tensile stress-strain behaviors. The softening temperature of the composite film was lower than that of a homogeneous PAI film. At a high temperature, Kevlar fibers may act as a thermal conductor and lower the softening point of the PAI composite. The mechanical properties of the composite film at a high temperature are mostly controlled by the PAI matrix.     

Constrained Sintering of Silver Circuit Paste

Densification kinetics and stress development during constrained sintering of a silver film on a rigid silicon substrate have been studied. Compared with free sintering, the sintering of constrained silver film exhibits a much lower densification and slower densification kinetics. The densification-controlled mechanism changes from fast grain-boundary diffusion kinetics for free sintering to slow lattice diffusion kinetics for constrained sintering. The in-plane tensile stress developed during constrained sintering of silver film, measured using a noncontact laser-scanning optical system, increases rapidly to a maximum level of 1.0–1.5 MPa initially, gradually decreases, and then becomes constant at 0.8–1.0 MPa. The maximum stress observed increases with increasing sintering temperature as a result of the faster densification rate. It is believed that the retardation of densification kinetics of constrained silver film is caused by a change in densification mechanism and the existence of in-plane tensile stress.     

Investigation of cracks in GaN films grown by combined hydride and metal organic vapor-phase epitaxial method

Cracks appeared in GaN epitaxial layers which were grown by a novel method combining metal organic vapor-phase epitaxy (MOCVD) and hydride vapor-phase epitaxy (HVPE) in one chamber. The origin of cracks in a 22-μm thick GaN film was fully investigated by high-resolution X-ray diffraction (XRD), micro-Raman spectra, and scanning electron microscopy (SEM). Many cracks under the surface were first observed by SEM after etching for 10 min. By investigating the cross section of the sample with high-resolution micro-Raman spectra, the distribution of the stress along the depth was determined. From the interface of the film/substrate to the top surface of the film, several turnings were found. A large compressive stress existed at the interface. The stress went down as the detecting area was moved up from the interface to the overlayer, and it was maintained at a large value for a long depth area. Then it went down again, and it finally increased near the top surface. The cross-section of the film was observed after cleaving and etching for 2 min. It was found that the crystal quality of the healed part was nearly the same as the uncracked region. This indicated that cracking occurred in the growth, when the tensile stress accumulated and reached the critical value. Moreover, the cracks would heal because of high lateral growth rate.