高比重钨合金准静态和动态断裂韧性研究

文章研究了高比重钨合金95W-3.5Ni-1.5Fe在准静态和动态加载下的断裂特性,开展实验测试了该材料在准静态和动态加载下的断裂韧性。准静态试验利用三点弯半圆形试样在万能试验机上加载,并根据测试标准ASTM E399得到了准静态断裂韧性。动态加载则是利用三点弯半圆形试样在霍普金森压杆上进行冲击加载,分析了试样在冲击过程中的动态力平衡条件,并依照准静态方法计算了钨合金在不同冲击速率下的动态断裂韧性,最后讨论了加载速率对钨合金断裂韧性的影响。     

三维编织复合材料准静态侵彻性能实验研究

本文研究不同厚度的三维编织芳纶 /环氧树脂复合材料在不同侵彻角下的准静态侵彻情况 ,分析准静态侵彻载荷—位移曲线及其破坏机理 ,比较不同厚度的三维编织复合材料在相同侵彻角下的位移—载荷曲线 ,和相同厚度的三维编织复合材料在不同侵彻角下的位移—载荷曲线 ,为深入研究三维编织复合材料的准静态侵彻性能和动态侵彻性能打下一些基础。     

铜基粉末冶金摩擦材料冲击时的动态力学特征

在分离式Hopkinson压杆(SHPB)上做了铜基粉末冶金摩擦材料在102s-1～103s-1应变率范围内的冲击试验,弹速范围为4 m/s～15 m/s,在透射杆上采用了半导体应变片技术;在MTS实验机上做了该材料在10-4s-1～10-3s-1应变率范围内的准静态实验,分别在应变为0.005,0.010,0.020,0.035时卸载再加载,以验证材料的黏弹塑性特征.通过分析动态和静态实验曲线,发现该材料在应变率300 s-1和准静态时有应变硬化效应,但在应变率500s-1以上却反映出应变软化效应,因此该材料为含损伤非线性黏弹塑性材料.该结论可推广应用于类似烧结合金的材料,实验给出的该材料动态和静态数据,为工程设计提供了可靠的依据.     

角联锁复合材料的拉伸破坏

为说明角联锁机织复合材料在准静态拉伸加载下的破坏行为,通过实验分析的方法,考察了材料的应力-应变曲线以及破坏形态,说明了角联锁机织复合材料在准静态拉伸载荷下的破坏模式与机制。结果表明:角联锁机织复合材料在整个拉伸过程中经历了3个阶段。此外,树脂碎裂、纱线的断裂抽拔是角联锁机织复合材料在准静态拉伸加载下的主要破坏模式,且材料断口较为整齐,断口处可发现纱线上几乎不黏附树脂,说明拉伸过程中纱线与树脂界面发生脱黏现象。     

填经纱对三维角连锁结构复合材料准静态侵彻性能的影响

为研究填经纱对三维角连锁结构增强复合材料准静态侵彻性能的影响,以玻璃纤维为原料制备4种经向截面结构具有不同填经纱层数的三维角连锁结构机织物,并以真空辅助成型工艺获得复合材料,采用集中准静态压痕试验方法获得侵彻位移载荷、位移瞬时能量吸收量曲线,分析材料在准静态侵彻下的力学响应历程及特性。结果表明,在立体织物的经向增加填经纱,各组填经纱在复合材料的位移瞬时能量吸收量曲线中均对应有明显的能量吸收区,使复合材料所能承受的最大侵彻载荷和能量吸收能力增加,但复合材料的破坏位移却减少。     

纸浆模塑材料的弹黏塑性模型及实验验证

在准静态等速拉伸实验得出的纸浆模塑材料应力-应变曲线的基础上,分析了纸浆模塑材料在变形过程中存在的初始弹性阶段、黏塑性阶段和断裂破坏阶段,建立了表征纸浆模塑材料弹黏塑性的流变模型.2种不同纸浆模塑材料的实验表明,实验结果与理论模型比较吻合.     

新型纬编间隔织物及其复合材料的冲击性能

开发了一种双层V形(三角形)间隔层纬编间隔织物(WKSF)编织工艺，并在STOLL电脑横机上编织双层V形与双层U形WKSF,分别研究了两种织物的横向和纵向断裂拉伸性能。通过试验得到拉伸载荷-位移曲线。结果表明，双层V形间隔结构织物的横向拉伸性能优于双层U形间隔结构。同时研究了浸渍剪切增稠液(STF)的WKSF(STF-WKSF)冲击行为。通过冲击载荷-位移与能量吸收-位移曲线可知，在相同的冲击速度下，STF-WKSF比纯WKSF具有更低的峰值力和更高的能量吸收，STF可以有效提高织物的抗冲击性能；在不同的冲击速度下，双层V形结构的STF-WKSF比双层U形结构具有更好的缓冲性能。双层V形STF-WKSF可以用作人体局部缓冲保护材料。     

变刚度床垫空气弹簧刚度特性及影响因素

研究变刚度床垫中所使用的空气弹簧刚度特性及影响因素,空气弹簧是一种在使用过程中通过调整某些参数能够改变其刚度的弹簧结构。应用准静态力学试验研究了空气弹簧的气囊层数、形状、初始气压、材料编织层密度对其载荷-位移关系及刚度特性的影响。研究发现空气弹簧刚度曲线按照位移占弹簧总高度的比例可分为线弹性阶段与超弹性阶段2个具有不同刚度变化特征的阶段;空气弹簧的层数与刚度为负相关关系;空气弹簧的初始气压在线弹性阶段与刚度为正相关关系,但在超弹性阶段二者为负相关关系;空气弹簧的材料编织层密度与刚度为正相关关系。通过调整空气弹簧的初始高度、有效接触面积、气压与材料可以控制空气弹簧的刚度曲线,为空气弹簧设计及其在变刚度床垫上的应用提供实验依据。     

三维角联锁机织复合材料的冲击破坏有限元模拟分析

为研究层层接结三维角联锁机织复合材料的抗高速冲击性能,以指导抗冲击材料的结构设计,通过有限元分析的方法,计算此材料在具有不同入射速度弹体冲击下的动态响应。通过对比各种冲击条件下弹体的速度与时间曲线、加速度与时间曲线、材料渐进破坏扩展及最终破坏形态等的结果发现：冲击过程中,弹体的速度变化可被划分成2个阶段;弹体的加速度波动情况可直接反映复合材料靶体吸收弹体动能的动态规律;此外,经纱发生波浪状屈曲的区域是该类材料的重要结构部位,应在设计抗冲击型三维角联锁机织复合材料时进行局部强化与结构优化。     

膝盖防护用材料动态缓冲性能研究

为研究老年人摔倒时膝盖部位的防护装置,探讨经编间隔织物和聚氨酯海绵的动态缓冲性能。采用改进后的动态冲击方法模拟老年人摔倒时的受力情况,通过分析接触刚度系数,冲击力与位移曲线,冲击力与时间曲线,以及冲击能量与时间曲线反映材料的动态缓冲性能。此外,通过定义缓冲系数进一步表征试样缓冲性能,并分析试样的结构参数和缓冲系数之间的关系。结果表明,一定硬度的聚氨酯海绵具有较好的能量吸收性能,通过聚氨酯海绵和经编间隔织物的复合可得到缓冲性能较好的材料。     

三维正交机织复合材料的冲后压缩性能

为揭示纱线张力对三维机织复合材料抗冲击及冲后压缩性能的影响规律,基于多剑杆织造工艺,配置不同接结纱张力(25、50、100 cN)织造三维正交机织物,通过真空辅助树脂传递模塑成型工艺制备复合材料,并在室温下进行低速冲击及冲后压缩性能测试。结果表明：当接结纱张力为100 cN时,试样在冲击载荷下发生表层树脂大面积破裂和剥离并使纬纱失去支撑,同时,试样表层纬纱发生较大卷曲,促使压缩载荷发生屈曲失效;接结纱张力为100 cN试样的压缩性能相比接结纱张力为25 cN试样下降约50%;接结纱张力较高时易导致纬纱卷曲增大和树脂富集,并由此降低试样的弯曲刚度和冲后压缩性能。     

微波加热对马铃薯淀粉颗粒内部水状态及分布的影响

为了明确微波在淀粉物料加热过程中的机制,本实验选取典型B型淀粉-马铃薯淀粉作为研究对象,根据微波加热的升温规律,建立和评价可对照的加热模型,运用低场核磁共振技术,以Carr-Purcell-Meiboom-Gill(CPMG)脉冲序列为手段,通过对微波加热、快速加热和慢速加热等三种加热方式下样品的横向弛豫时间(T2)衰减曲线进行PCA分析,利用多指数回归拟合计算得到T2,从而分析样品内部水分的变化信息,研究微波加热对马铃薯淀粉颗粒内部水状态及分布的影响。结果表明三种加热方式对样品T2的影响具有显著性差异,具体表现为在糊化前期及糊化刚开始阶段,微波加热对马铃薯淀粉颗粒内水分分布有显著影响,本实验一定程度上证明了微波的特殊效应在该阶段对马铃薯淀粉内氢键的破坏有促进作用。     

Dynamic analysis on the functional relationship of pressure,displacement and angle for the top part of men's socks using FEM

The inward displacement perpendicular to the body surface produced by external pressure is an important index to evaluate the pressure comfort and optimal design of apparel products. In this paper, we studied on the functional relationship of pressure, displacement and angle when the body was in dynamic state after dressing. The dynamic pressure was divided into two parts: pressure with time (instantaneous, 1, 2, 4, 8 and 12?h) and pressure with movement (walking which described as upright position, leg lift 10°, leg lift 30° and foot backward off the ground). The displacement of each point on the lower leg cross section in four stages of walking process and six periods of time were simulated by ANSYS finite element software. After fitting, the functional curves between pressure/displacement ratio and the angle were obtained. By comparing, we found out that all the curves were presented nearly complete uniform curving form no matter what state of the human body was in. That is, when the human body was under clothing pressure, the corresponding displacement value on the body surface can be calculated on the premise of the known pressure value at any point of lower leg cross section during the wearing process by functional equation. All these solutions supplied a theoretical reference for optimal design of the top part of men’s socks.     

MECHANICAL PROPERTIES OF SATSUMA ORANGE AS RELATED TO THE DESIGN OF A CONTAINER FOR BULK TRANSPORTATION1

The mechanical properties of Satsuma oranges were studied under static, quasi-static and impact loading in order to determine conditions leading to minimum fruit injury in containerized shipping. The results indicated that the use of containers is safe for a 70h transport provided the stacking height does not exceed 70 cm. The static load at the bottom of the container should not exceed 2 kg per fruit if permanent deformation is to be avoided; the fruit ruptures when the load exceeds 4.2 kg per fruit. The time-deformation curve under static load was explained with a Burgers model modified with a sliding element. Bruising energy by impact was 3 times and that by quasi-static loading 1.4 times as great as that by static loading. The relationship between impact acceleration and dropping height of single fruits agreed well with the Hertz’ theory of colliding spheres for dropping heights up to 15 cm.     

柔性涤纶吊装捆绑带的耐动态疲劳性能

针对吊装捆绑带在循环使用过程中,因其力学性能和抗冲击性能易急剧恶化而影响其使用寿命的问题,通过对柔性涤纶吊装捆绑带分别进行多次循环定伸长和定载荷处理,对其耐疲劳性能进行了研究。结果表明:柔性涤纶吊装捆绑带在拉伸过程中呈现明显的胡克区、屈服区和增强区3个变化阶段;在较小形变(小于1%)或较小负载(小于断裂强力的10%)时,以急弹性形变为主;在较大形变或较大负载时,产生了破坏性的塑性形变,且不断累积;经过循环处理后,吊装捆绑带的断裂强力、断裂伸长率以及耐疲劳性能都急剧衰减,抗冲击性能下降显著,大大影响了其使用寿命。     

Impact performance of two bamboo-based laminated composites

The present work aims to determine the impact performance of two bamboo-based laminated composites [bamboo/poplar laminated composite (BPLC) and bamboo/glass fiber laminated composite (BGFLC)] using low-velocity impact tests by a drop tower. In addition, fracture characteristics were evaluated using computed tomography (CT). Results showed that BPLC presented better impact properties in both directions than BGFLC. Three stages are noted in impact load–deflection curves. The load–deflection curve characteristics of two composites are different in different stages. Matrix cracking, fiber-matrix interface debonding and delamination, and fiber breakage are the three main fracture mechanisms of two composites. Structural characteristics of the components and bonding strength are the important factors for impact properties and fracture mechanism of both bamboo-based laminated composites.     

即热型预制黑椒鸡柳加工过程中挥发性风味演化研究

目的 探究即热型预制黑椒鸡柳在加工过程中挥发性风味的动态演化过程。方法 利用气相色谱-离子迁移谱法(gas chromatography-ion mobility spectrometry, GC-IMS)检测标准化加工条件下预制鸡柳在不同加工阶段样品中挥发性化合物的差异性变化。结果 GC-IMS定性结果表明: 在预制加工的4个关键环节样品中共检测出97种主要挥发性风味化合物。归一化处理结果表明预制鸡柳中主要香气贡献物质为醇类、酮类、醛类、酯类、烯类、酸类化合物, 其相对含量占总体挥发性风味化合物含量的85.62%, 且在加工的不同阶段其挥发性化合物有显著变化差异。结论 GC-IMS技术有效区分出了预制鸡柳在不同加工阶段挥发性风味物质的差异性, 全面揭示了挥发性风味物质的动态演化过程, 对即热型预制鸡柳加工中挥发性风味控制提供了理论依据。     

Experimental study on the bending fatigue behaviors of 3D five directional braided T-shaped composites

The static three-point bending properties and cyclic bending fatigue performances of three-dimensional five-directional braided T-beam composite (3D5DBTC) have been investigated at room temperature. The fatigue life of 3D5DBTC under different stress levels was analyzed based on the obtained S–N curves. The load–displacement hysteresis loops curves and stiffness degradation curves were recorded to reveal the relationship between stiffness degradation and damage evolution. It is shown that there were three distinct stages corresponding respectively to matrix cracks, interface debonding, and fiber breaking in the whole fatigue loading. In addition, to understand the ultimate fracture failure mechanism of 3D5DBTC under the different fatigue loading conditions, the damage morphologies of 3D5DBTC after fatigue testing were observed by macrographs and SEM micrographs. The matrix crack and the resin–yarns interface debonding occurred on the flange while fiber breakages occurred in the web. Meanwhile, macrographs and SEM images confirm that fiber breaking is the dominant damage under the high stress level, while matrix cracking and interfacial debonding are the main failure modes at low stress level.