Measurement of the Timoshenko Shear Stiffness. II: Effect of Transverse Compressibility

This is the second of two papers devoted to the issue of measuring the Timoshenko shear stiffness of thin-walled composite beams. In the first paper, the effect of warping on the effective Timoshenko shear stiffness, as measured through bending tests, was studied. The bending test was simulated using finite-element analysis, and the results indicated that the warping effect was minimal. On the other hand, the evidence suggests that transverse flexibility may have a significant influence on the effective Timoshenko shear stiffness, decreasing the effective shear stiffness at shorter test spans. The purpose of the present study is to further investigate this effect and to explore the use of a sandwich theory to predict the measurement error. A higher-order sandwich theory, which captures the transverse strain at concentrated loads and supports, is applied to a commercially available thin-walled composite beam. The results indicate that the sandwich model does capture the decrease in the effective shear stiffness at short spans, and the dependence of the shear stiffness on span-to-depth ratio is similar to that calculated in the first paper, using the finite-element method.     

气辅成型中成型工艺对制品翘曲的影响

对气辅成型制品翘曲缺陷采用正交实验方法和数值模拟方法进行了研究。研究了气体注射延迟时间与气体注射压力及气体注射时间与气体注射压力两对工艺参数的交互作用对制品翘曲缺陷的影响。结果表明,对制品翘曲影响最为严重的是气体注射时间与气体注射压力的交互作用。较长的延时可以减轻制品翘曲的程度,但气体无法穿透或穿透不足等问题也是延时过长会造成的,因此选择合适的气体注射时间与气体注射压力以及气体延时组合非常重要。     

采用RFR-GA算法的薄壁注塑件质量多目标优化

汽车内饰件可由注塑加工获得,但成型过程中塑件产生的翘曲、体积收缩较大,针对该问题,以某汽车薄壁注塑件为例,研究了其注塑工艺参数的优化方法.通过以注塑过程中的最小翘曲和最小体积收缩率为目标函数,以注塑温度、模具温度、注射压力、保压压力、保压时间以及冷却时间等参数作为设计变量,构建了多目标全局优化模型.利用Moldflow...     

Comprehensive Warpage Analysis of Stacked Die MEMS Package in Accelerometer Application

<正>Packaging of MEMS ( micro-electro-mechanical system ) devices poses more challenges than conventional IC packaging, since the performance of the MEMS devices is highly dependent on packaging processes. A Land Grid Array ( LGA ) package is introduced for MEMS technology based linear multi-axis accelerometers. Finite element modeling is conducted to simulate the warpage behavior of the LGA packages. A method to correlate the package warpage to matrix block warpage has been developed. Warpage for both package and sensor substrate are obtained. Warpage predicted by simulation correlates very well with experimental measurements. Based on this validated method, detailed design analysis with different package geometrical variations are carried out to optimize the package design. With the optimized package structure, the packaging effect on accelerometer signal performance is well controlled.     

塑料盖注塑成型方案分析及翘曲变形参数优化

以塑料盖作为研究对象,获得最优成型方案,预测塑件成型后的翘曲变形程度以提高塑件质量。初步提出两种注塑工艺方案加工塑料盖,使用Moldflow软件对两种方案注塑过程进行模拟对比分析,对产生翘曲缺陷的原因进行研究;利用五因素四水平的正交试验,以减小翘曲变形程度作为优化目标,优化工艺参数。模拟结果表明:方案二为最优方案,且翘曲变形主要是由收缩不均匀以及取向不均匀而造成的,翘曲变形程度最小的工艺参数组合为熔体温度250℃、模具温度60℃、保压时间12 s、冷却时间12 s、填充时间0.9 s,优化后比优化前翘曲变形程度降低9.4%左右,熔料熔接和材料性能也有所改善,塑料盖整体质量提高。实验可有效地缩短塑料盖的研发周期,降低生产成本,提高塑料盖的研发成功率。     

Simultaneous Control of Birefringence and Warpage for Thermoplastic Optical Lenses Fabricated Using Microinjection Molding

Achieving tight tolerances for multiple properties of a single product becomes a key issue. This study presents an investigation on birefringence and warpage of thermoplastic lenses prepared using microinjection molding, aiming to identify the significant factors, and simultaneously control both properties for optical applications. The birefringence along the flow changed more drastically than that in the cross-flow direction. Meanwhile, two warpage shapes of the lenses could be observed and their formation mechanisms were discussed. The simultaneous control of both properties was accomplished through multi-objective optimization using the desirability function approach. Finally, the optimal processing parameters were obtained and experimentally verified.     

Effect of monomer content on physical properties of silicon nitride ceramic green body prepared by gelcasting

The gelcasting technique was employed to prepare Si₃N₄ green body. The monomers used in the research were acrylamide (AM) and N,N′-methylenebisacrylamide (MBAM). The influences of the monomer content (AM and MBAM) and the ratio of monomers (AM/MBAM) on the warpage rate, shrinkage rate, and the flexural strength of Si₃N₄ ceramics green body were investigated. Both warpage rate and shrinkage rate of green body were found to decrease with the increase of monomer content, and monotonically increase with the ratio of monomers after drying. The variation of warpage rate with the ratio of monomers is evident when monomer content is 20 wt.%, but the variations are not evident when monomer contents are 40 and 55 wt.%. The flexural strength of the green body is highest at an optimum value of the monomers ratio, and increases with increasing monomer content, reaching 50–90 MPa when monomer contents are 40 and 55 wt.%.     

薄壁塑件注射成型工艺参数优化

在注射成型过程中将计算机模拟技术和实验优化设计相结合,以相机外壳为例利用MoldFlow对各工艺参数进行注射成型过程的模拟.通过分析塑件体收缩变形和翘曲变形的原因,得出熔体温度是影响塑件体收缩变形的主要因素,而保压压力对翘曲变形起主导作用力.并在正交试验的指导下优化工艺参数,使收缩率和翘曲变形分别降为原来的75.9%和87.0%.     

键合技术中键合胶残余应力检测的实验研究

通过检测受到键合胶残余应力影响的芯片表面的翘曲特征和力学特性,运用泰曼-格林干涉仪与力学实验机相结合,成功地分析了在采用粘胶键合中,粘胶硬化后残余应力对芯片的影响以及产生的原因,对键合胶的选择提出了科学的依据。本文对这种方法进行了理论分析和实验验证。     

Efficient warpage optimization of thin shell plastic parts using response surface methodology and genetic algorithm

During the production of thin shell plastic parts by injection molding, warpage depending on the process conditions is often encountered. In this study, efficient minimization of warpage on thin shell plastic parts by integrating finite element (FE) analysis, statistical design of experiment method, response surface methodology (RSM), and genetic algorithm (GA) is investigated. A bus ceiling lamp base is considered as a thin shell plastic part example. To achieve the minimum warpage, optimum process condition parameters are determined. Mold temperature, melt temperature, packing pressure, packing time, and cooling time are considered as process condition parameters. FE analyses are conducted for a combination of process parameters organized using statistical three-level full factorial experimental design. The most important process parameters influencing warpage are determined using FE analysis results based on analysis of variance (ANOVA) method. A predictive response surface model for warpage data is created using RSM. The response surface (RS) model is interfaced with an effective GA to find the optimum process parameter values.