Extension of the Localized Plastic Flow Zone in Simple Shear

Propagation of localized plastic shear in a thin layer of metal was studied. An increase in the rate of propagation of the localized shear when moving away from the site of its initiation was established. The propagation rate of strains of a given level approaches the elastic shear-wave velocity in metal when moving away from the site of initiation of the localized shear.     

搅拌针端部挤压区内塑性金属的流动行为

以0.02 mm厚的铜箔作为标示材料、1 mm和2 mm厚的2024铝合金薄板作为基材,采用不同的叠加方式组成叠层并进行搅拌摩擦焊接(Friction stir welding, FSW)试验,分析搅拌针端部挤压区塑性金属的流动行为及其对焊缝成形的影响。结果表明,在FSW焊接过程中,焊缝上部被塑化的金属不断地沿着搅拌针螺纹旋向往搅拌针端部迁移、长大,形成挤压区。此挤压区由位于搅拌针两侧的扩展区和位于搅拌针端面下方的变形区组成。其中,变形区的金属一部分来自从焊缝上部迁移而来的塑性金属;另一部分来自搅拌针端面下方母材经旋转摩擦作用而发生塑性变形的金属。挤压区塑性金属的流动方式分为轴向挤压迁移、水平摩擦迁移和绕流迁移三种。对厚板进行FSW焊接时,挤压区的塑性金属倾向以绕流迁移方式为主,导致焊缝内部形成疏松区或孔洞型缺陷。     

中阻值导电塑料（浆料）的研制及性能研究

本文介绍了一种中阻值导电塑料(浆料)的研制及其电阻率、温度系数和粘度的测量,讨论了老化的原因及结果。     

非饱和土的塑性体应变与剪应变的相互作用原理

将岩土塑性体应变与剪应变的相互作用原理拓展到了非饱和土领域。除了塑性体应变与剪应变的相互作用外,在非饱和土中出现了两类新的相互作用,吸力-塑性体应变和孔隙气压力-塑性体应变。吸力具有二重性质,其对塑性体应变作用包括两个相反的方面。基于吸力性质,阐明了非饱和土的一些独特的性质,诸如有效应力参数的物理涵义,吸力对体积变化和前期固结压力的影响和湿陷机理等。另外,应用拓展的塑性体应变与剪应变相互作用原理,从理论上证明了非饱和土的临界状态线是存在的和唯一的,以及它与应力历史无关。     

退役乘用车保险杠塑料同等性能再利用探索

预计到2020年,我国乘用车报废量将达到800万辆,其中报废乘用车塑料量超过100万吨。目前,我国退役乘用车塑料回收利用处于起步阶段,行业管理混乱,回收技术落后,污染严重,且尚未实现回收乘用车塑料再利用价值最大化。因此,迫切需要深入研究乘用车塑料高附加值回收利用方式,推动该回收行业快速、健康发展,促进汽车工业可持续发展。文中以退役乘用车保险杠塑料为研究对象,通过研究得出其再生产相应汽车零部件同等性能回收利用技术方案,并依据该流程试制了含再生塑料的保险杠,并对含再生的保险杠进行了全面的分析研究。结果表明,含30%再生料保险杠的各项性能均满足生产要求。该研究为再生汽车塑料实现同等性能等高附加值再利用提供了借鉴。     

压制模型腔的等温成形与超塑性成形研究

模具型腔的等温成形与超塑性成形是一种新的制模工艺,这一工艺所具有的优点使之成为模具型腔制造的一种有力手段。本文重点介绍了热固性塑料压制模型腔的等温成形与超塑性成形工艺,介绍了有关的工艺参数、工装设计,并阐述了该工艺的应用实例。     

TA1钛合金药型罩剪切旋压成形塑性变形规律的数值模拟研究

目的 TA1钛合金作为药型罩材料,具有提高穿深和侵彻孔径的优异表现,但其剪切旋压成形过程中塑性变形规律复杂且难于控制,以期通过有限元数值计算解析多工艺参数的协同作用。方法 建立了TA1薄壁锥形件结构旋压加工过程的三维非线性热-力耦合有限元模型,研究了TA1从圆形板坯到锥形件旋压全过程的金属塑性变形行为、应力及应变的变化。采用正交实验分析了旋轮进给速率、芯轴转速与板坯厚度对成形过程的旋压力以及成形样件的内径偏差和壁厚偏差的影响规律。结果 结果表明,锥形件侧壁的塑性应变沿母线方向逐渐减小,最大应变值出现在靠近锥形件顶部的小端面位置。旋压载荷随旋轮进给速率与板坯厚度增加而增加,随芯轴转速增加而减小。内径偏差随进给速率与板坯厚度的增加而减小,与芯轴转速的相关性较小。壁厚偏差随进给速率的增加先减小后增大,随芯轴转速与板坯厚度的增加而减小。结论 基于数值模拟结果,获得TA1薄壁锥形件的优化工艺参数为:旋轮进给速率300 mm/min,芯轴转速260 r/min,板坯初始厚度4 mm。开展了TA1钛合金剪切旋压成形实验,所得锥形件尺寸与模型计算结果一致,验证了模型的准确性。     

论岩土塑性体应变与剪应变的相互作用原理

对岩土塑性变形过程中体应变与剪应变的相互作用原理的内涵做了深入的阐述，特别对塑性体应变和剪应变之间的相互作用方式，塑性体应变对抗剪能力的直接控制作用，剪缩和剪胀发生的条件，应力路径相关性是这种相互作用的综合体现及实例验证，临界状态是塑性和弹性体应变都保持不变的纯粹剪切变形过程等方面进行了论证；根据这个相互作用原理，在理论上证明了空间临界状态线的存在性和唯一性以及它与应力是无关的。     

Evaluation of rheological properties of lead-free solder pastes and their relationship with transfer efficiency during stencil printing process

Although stencil printing is widely used in surface mount technology, it is believed to be the main source of majority of defects in the final assembly. Such defects, which could lead to major reliability issues, can be controlled and/or minimised through proper understanding and control of the flow and deformation behaviour of solder pastes. This study concerns the characterisation of three different Pb-free solder pastes used for ultra-fine pitch assembly applications. We also investigate the paste transfer efficiency through linearly varying stencil apertures sizes, and correlate the paste rheological properties with their transfer efficiency – to provide further understanding of the effects and interactions of stencil printing process variables on the paste transfer efficiency. Three rheological tests, namely: the viscosity, thixotropic and oscillatory amplitude sweep were employed in the characterisation. The paste samples were printed on Cu substrates using stencil printing (with varying aperture cavity dimensions in the range 0.79 mm³–1.62 mm³). A three-level design on two factors experiment, 3², was used to determine significant level of parameters in terms of main effect and interactions. Our results show that the paste type and volume of stencil aperture interact during printing and that pastes with unique rheological properties produced distinctive transfer pattern. The results also show that the printing process variables and their interactions were significant on transfer efficiency of pastes. These results will be of interest to R&D staff involved in formulation of new Pb-free pastes and the design of stencils for ultra-fine pitch assembly applications.     

泡沫塑料/瓦楞纸板组合结构的缓冲性能

目的分析比较不同种类缓冲材料组合结构的缓冲性能。方法将EPS和EPE分别与单、双瓦楞纸板进行叠合,获得4种组合结构件,对上述缓冲材料进行静态压缩试验。结果得到不同材料的应力-应变曲线及缓冲系数曲线。结论泡沫塑料/双瓦楞纸板的应变能大于泡沫塑料/单瓦楞纸板;EPE/双瓦楞纸板的缓冲性能相对于EPS/双瓦楞纸板来说更为优异;泡沫塑料/双瓦楞纸板的最小缓冲系数低于相对应的泡沫塑料。     

用于锂电池包装的铝塑膜印刷封装新工艺

目的研发一种铝塑膜印刷封装的新工艺,提高锂电池包装的生产效率。方法通过对铝塑膜表面先涂布、再印刷、后封装的工艺替代行业内铝塑膜包装锂电池的传统工艺,测试新工艺条件下铝塑印刷膜的耐化学性、耐磨性、附着力及光泽度等指标。结果采用新工艺后,不仅可以拓宽印刷种类,提升生产效率,而且能够实现高精度印刷作业,提高铝塑膜的印刷质量。试验表明,该工艺条件下的铝塑印刷膜耐化学性和耐磨性优良,附着牢度可达100%,平均光泽度为8.4。结论新工艺相比传统工艺具有较强的先进性,可适用于手机锂电池的铝塑膜印刷封装作业。     

NURBS造型理论及其在产品造型设计中的应用

产品造型过程中常需要将设计产品虚拟出来以实现设计模型化。运用计算机绘制虚拟模型的方式有网格、面片以及NURBS等多种；但NURBS造型方式目前是最好的，尤其在建立复杂曲面模型方面更体现出其优越性。NURBS造型方式的应用遍及工业、军事、艺术等许多领域。     

Homogeneous Plastic Flow of Fully Amorphous and Partially Crystallized Zr41.2Ti13.8Cu12.5Nil0Be22.5 Bulk Metallic Glass

The homogeneous plastic flow of fully amorphous and partially crystallized Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercooled liquid region. Experimental results show that at sufficiently low strain rates, the supercooled liquid of the fully amorphous alloy reveals Newtonian flow with a linear relationship between the flow stress and strain rate. As the strain rate is increased, a transition from linear Newtonian to nonlinear flow is detected, which can be explained by the transition state theory.Over the entire strain rate interval investigated, however, only nonlinear flow is present in the partially crystallized alloy, and the flow stress for each strain rate is much higher. It is found that the strain rate-stress relationship for the partially crystallized alloy at the given temperature of 646 K also obeys the sinh law derived from the transition state theory, similar to that of the initial homogeneous amorphous alloy. Thus, it is proposed that the flow behavior of the nanocrystalline/amorphous composite at 646 K is mainly controlled by the viscous flow of the remaining supercooled liquid.     

Pseudo-elastic description of polymeric foams at finite deformation with stress softening and residual strain effects

Polymeric foams are typical materials for energy absorber in such areas as aircraft, car industry and in the field of electronic packaging. Besides the typical hyperelastic behaviour, non-linear stress–strain behaviour in large elastic deformation, polymeric foams may also exhibit some inelastic effects, like stress softening and residual strain. In this paper we first describe some experiment results that illustrate the stress softening in compressible expanded polypropylene (EPP) foams together with associated residual strain effects. Then, based on Ogden and Dorfmann’s results, a pseudo-elastic model is introduced to capture the stress softening and residual strain effects by including of two variables in the energy function. Numerical simulations of uniaxial-compression tests of two types of EPP foam are used to determine the material parameters of Ogden’s model, stress softening and residual strain effects. The numerical simulations indicate that the pseudo-elastic model provides reasonably accurate predictions of the inelastic behaviour of polymeric foam.     

Shear design of reinforced concrete beams with FRP longitudinal and transverse reinforcement

The shear resisting mechanisms of reinforced concrete (RC) beams with longitudinal and transverse FRP reinforcement can be affected by the mechanical properties of the FRP rebars. This paper presents a mechanical model for the prediction of the shear strength of FRP RC beams that takes into account its particularities. The model assumes that the shear force is taken by the un-cracked concrete chord, by the residual tensile stresses along the crack length and by the FRP stirrups. Failure is considered to occur when the principal tensile stress at the concrete chord reaches the concrete tensile strength, assuming that the contribution of the FRP stirrups is limited by a possible brittle failure in the bent zone. The accuracy of the proposed method has been verified by comparing the model predictions with the results of 112 tests. The application of the model provides better statistical results (mean value V_test/V_pred equal to 1.08 and COV of 19.5%) than those obtained using the design equations of other current models or guidelines. Due to the simplicity, accuracy and mechanical derivation of the model it results suitable for design and verification in engineering practice.     

脉冲时滞积分-微分系统解的非振动性和渐近性

讨论了脉冲时滞积分-微分系统解的非振动性和渐近性，得到了时滞积分-微分系统在脉冲扰动下解的非振动性和渐近性的充分条件。     

涡式粉尘分选机的机理分析与设计

在机理分析的基础上导出了被分选的飞灰质量流量Ms 的计算式 ,对已知的运行条件下 ,可作为设计分选机的依据     

框剪结构高楼纵向倾倒拆除爆破研究

我国目前用爆破法拆除的高层楼房主要是框剪结构。根据同一楼房中框架部分与剪力墙部分的相对位置、倒塌方向选择、前后段起爆时差,对框剪结构楼房爆破效果的影响等进行了分析,给出了楼房爆破切口倾角(闭合角)的经验数据、理论计算方法及确保楼房倒塌的判据,指出了楼房沿其纵向倒塌的难度远大于横向倒塌,并以靖江金都大厦的爆破为例,详细介绍了楼房沿其纵向倾倒时的爆破方案确定、预处理方法、爆破切口要素、立柱的爆破破坏高度、药孔参数、爆破参数、起爆网路等。靖江金都大厦为框剪结构的11层高楼,因环境限制,需要沿其不利于倒塌的纵向倾倒,而剪力墙结构却位于高楼的纵向两端,对该大楼的倒塌带来极大难度,通过精心设计其爆破方案,优化爆破参数,并采取严格的安全技术措施,完全达到了预期的爆破效果。