鞍面力-位移分控多点成形起皱的数值模拟研究

在多点成形中,起皱是影响板材成形质量的重要因素。针对鞍面在力-位移分控多点成形方式下的起皱,以ABAQUS为模拟分析平台,模拟了鞍面的成形过程,并分析了其起皱缺陷。研究结果表明:在鞍面力-位移分控多点成形过程中,当板厚较小(1和1.5 mm)时,板材中心区域发生了较为严重的起皱,且优先变形的方向发生的起皱现象更明显;随着板厚和曲率半径的增大,起皱趋势减小。针对起皱现象探明了起皱的原因,提出了鞍面起皱的抑制方法,并进行了模拟计算和成形试验,结果表明,增大成形力和错位都可以抑制起皱,错位并结合增大成形力可以显著改善板材成形质量。     

The origin of wrinkles on transferred graphene

When two-dimensional graphene is exfoliated from three-dimensional highly oriented pyrolytic graphite (HOPG), ripples or corrugations always exist due to the intrinsic thermal fluctuations. Surface-grown graphenes also exhibit wrinkles, which are larger in dimension and are thought to be caused by the difference in thermal expansion coefficients between graphene and the underlying substrate in the cooling process after high temperature growth. For further characterization and applications, it is necessary to transfer the surface-grown graphenes onto dielectric substrates, and other wrinkles are generated during this process. Here, we focus on the wrinkles of transferred graphene and demonstrate that the surface morphology of the growth substrate is the origin of the new wrinkles which arise in the surface-to-surface transfer process; we call these morphology-induced wrinkles. Based on a careful statistical analysis of thousands of atomic force microscopy (AFM) topographic data, we have concluded that these wrinkles on transferred few-layer graphene (typically 1–3 layers) are determined by both the growth substrate morphology and the transfer process. Depending on the transfer medium and conditions, most of the wrinkles can be either erased or preserved. Our work suggests a new route for graphene engineering involving structuring the growth substrate and tailoring the transfer process.      

羊毛角蛋白溶液在毛织物定型中的应用

采用自制的羊毛角蛋白溶液整理毛织物,通过正交试验选择合理的整理工艺参数,得到最优工艺为:羊毛角蛋白溶液用量15%(o.w.f)、处理温度75℃、处理时间60 min、浴比1∶25。对比整理前后毛织物的性能发现:毛织物毡缩率由17.85%下降到4.1%;急弹性回复角从144.2°提高到215°;断裂强力小幅提高而断裂伸长下降。整理后织物的毡缩率显著下降,折痕回复性提高,断裂强力增加而伸长下降,毛织物定型效果得到改善。     

Non-lithographic patterning of phage-displayed peptides with wrinkled elastomers

The development of controlled patterning of phage (viruses) could expand opportunities for both fundamental studies and creating various materials platforms. Inducing the elastomeric instability of PDMS film provides a non-lithographic, tuneable, controlled method for generating micro/nanoscale wrinkle patterns. Phage display has emerged as a powerful method for selecting peptides that possess enhanced selectivity and binding affinity toward a variety of targets. In this report, we demonstrate the non-lithographic patterning of phage-displayed peptides with wrinkled elastomers. Our results show that the phage-displayed peptides can be patterned on specific locations in controlled and tuneable ways, be transferred to other substrates and induce the self-assembly of hybrid materials. We anticipate that these results could open up exciting opportunities in fundamental studies and in applications ranging from sensors, hybrid materials, self-assembly, surface and interface, to micro/nanoelectronics.     

圆形构筑物周边土工膜沉降时的褶皱产生机理及分析模型

基于传统薄膜理论建立了下卧土体沉降作用下圆形构筑物周边土工膜受力变形的分析模型,发现在下卧土体沉降作用下圆形构筑物周边土工膜中将产生褶皱,并揭示了其产生机理。进一步通过引入"可变泊松比"概念并基于褶皱薄膜理论建立了褶皱区与张拉区土工膜受力变形的分析模型,分析了下卧土体沉降大小、上覆土压力、土工膜界面强度、圆形构筑物半径及土工膜抗拉刚度对土工膜褶皱程度与受力变形大小的影响。结果表明下卧土体沉降越大、圆形构筑物半径越小,则褶皱程度及土工膜最大应变越大。最后提出了工程上控制土工膜褶皱和最大应变与张力的几点工程措施。     

Design of Strain‐Limiting Substrate Materials for Stretchable and Flexible Electronics

Recently developed classes of electronics for biomedical applications exploit substrates that offer low elastic modulus and high stretchability, to allow intimate, mechanically biocompatible integration with soft biological tissues. A challenge is that such substrates do not generally offer protection of the electronics from high peak strains that can occur upon large‐scale deformation, thereby creating a potential for device failure. The results presented here establish a simple route to compliant substrates with strain‐limiting mechanics based on approaches that complement those of recently described alternatives. Here, a thin film or mesh of a high modulus material transferred onto a prestrained compliant substrate transforms into wrinkled geometry upon release of the prestrain. The structure formed by this process offers a low elastic modulus at small strain due to the small effective stiffness of the wrinkled film or mesh; it has a high tangent modulus (e.g., >1000 times the elastic modulus) at large strain, as the wrinkles disappear and the film/mesh returns to a flat geometry. This bilinear stress–strain behavior has an extremely sharp transition point, defined by the magnitude of the prestrain. A theoretical model yields analytical expressions for the elastic and tangent moduli and the transition strain of the bilinear stress–strain relation, with quantitative correspondence to finite element analysis and experiments.     

精锻身管弹膛内壁成形圈纹缺陷机理研究

精锻身管弹膛成形是弹线膛同锻工艺中的重点和难点,弹膛内壁的成形质量直接关系到身管的精度和使用寿命,内壁产生圈纹是弹膛部位主要的成形缺陷。分析弹膛在锻造过程中身管内壁材料的受力特点和流动情况,结合有限元仿真和试验研究,通过圈纹产生的位置分析圈纹产生的原因,并建立相关的判断准则。对比弹膛内壁材料应力分析曲线和枪管锻打试验结果,发现环向圈纹的产生与内壁受压失稳有关,弹膛内壁在锻造过程中的切向应力分量超过临界值即出现失稳起皱现象。进一步研究发现,弹膛部位的锻造段锻造比达到临界值时,内壁产生的圈纹会在后续锻打过程中被重新压平,消除弹膛成形缺陷。结果表明：身管弹膛内壁在锻造过程中切向压应力超过约2 150 MPa即 发生失稳从而产生环向圈纹;压平弹膛内壁环向圈纹的锻造段锻造比阈值约为28.5%.     

Inspecting anisotropy in wrinkle recovery angle of woven fabric

In this paper, the anisotropic wrinkle recovery properties of plain and twill fabrics are explored by studying the variations of the wrinkle recovery angle with sample orientation angle. Orientation angle is the angle measured counterclockwise from the weft direction to the sample’s long axis, that is, the crease direction. This study focused on inspecting anisotropy in wrinkle recovery to find more effective test angles for different woven fabrics. A dynamic wrinkle recovery tester was used to measure the recovery angles of specimens automatically which were cut in various directions. The trend of plain fabrics shows that its recovery angle generally increases at first and then decreases with the increase in the orientation angle. The trend of twill fabrics differs in folding ways. The experimental results revealed that the wrinkle recovery angles of the woven fabrics had the lowest values near the orientation angles of 0° and 90°, i.e. the warp and weft directions, and therefore these two traditionally used directions in the standard test method did not best reflect the wrinkle recovery yielded from both warps and wefts. The diagonal direction (45°) was proven to be the optimal orientation angle for a balanced plain fabric, while the two orthogonal directions, i.e. the twill direction and its perpendicular direction, were found to be more relevant for a twill fabric. Optimal orientation angles used to test the wrinkle recovery angle of a woven fabric should be associated with its structure.     

高粱黑色素染色后棉织物性能测试与分析

以天然高粱黑色素上染棉织物,探讨了不同条件下染色对棉织物拉伸特性、剪切特性、弯曲特性、压缩特性及表面特性的影响,以及对折皱回复角及毛效的影响。结果表明:高粱色素染色可提高织物柔软性、弹性、活络性及抗形变能力,降低织物粗糙度,但同时丰满感、抗剪切变形能力、折皱回复角、毛效有所降低。