冲击荷载下花岗岩残积土的滞回曲线特征与损伤定量评价

为评价冲击荷载下花岗岩残积土的损伤发展规律,基于不同振幅(A = 100 ～400 kPa)、频率(f=3 ～15 Hz)和围压(σ'3 =50 ～500 kPa)下室内循环冲击试验得到滞回曲线的形态特征,提出4个反映试样在冲击荷载下的能量消耗、损伤程度、刚度衰减和塑性应变发展特性的定量结构损伤参数:累积耗散能量EN、...     

不同缓冲压头下香梨静压损伤特性研究

目的解决库尔勒香梨在包装、运输过程中因静压产生的香梨损伤问题。方法在不同压缩速率、不同摆放位置、不同缓冲压头条件下,利用万能试验压缩机测量分析香梨机械特性参数变化规律。结果各压缩特性参数的分布规律大致相同,生物屈服极限、破坏极限、变形能、破坏能均随着压缩速率的增大逐渐增大,屈服极限、破坏极限在随压缩速率增大而增加的过程中有极值存在。香梨纵向部位压缩特性参数均大于横向部位压缩特性参数。在相同摆放位置下,泡沫缓冲压头的压缩特性参数最大,钢板压头下的特性参数最小。当速率为30 mm/min时,在泡沫缓冲压头下,香梨横向摆放时的生物屈服极限为105.98 N,变形能为242 N·mm,破坏极限为155.25 N,破坏能为582N·mm。香梨纵向摆放时的生物屈服极限为135.91 N,变形能为521 N·mm,破坏极限为177.07 N,破坏能为942 N·mm。结论不同缓冲压头下的压缩特性参数曲线分布规律大致相同,屈服极限和破坏极限在随压缩速率增大而增加的过程中有极值存在。香梨纵向摆放受到外界的机械损伤小于横向摆放所受的机械损伤,在香梨包装、贮藏、运输过程中应考虑摆放位置,尽可能让香梨纵向受力。当使用泡沫材质进行包装时,香梨机械损伤最小,在香梨包装时应考虑选用泡沫包装材质。     

多壁碳纳米管湿度传感器介电损耗模型（英文）

为揭示碳纳米管湿度传感器的介电损耗,制作了一种电阻型碳纳米管湿度传感器.使用介电损耗相关理论对其频率特性进行分析,并利用普适方程建立了传感器介电损耗模型.对实验数据与所建立模型进行拟合,得到拟合决定系数为0.994,表明可以使用普适方程对传感器介电损耗进行描述.由于测试频率引起的传感器电阻变化会改变传感器线性度,分析了不同测试频率下传感器的线性度,发现当测试频率为10 kHz时传感器的线性度最佳（1.52%）,此时传感器灵敏度为-7.83Ω/%RH.     

收获期马铃薯块茎跌落冲击特性及损伤规律研究

为了减少马铃薯机械收获中的损伤,揭示马铃薯块茎跌落冲击损伤机理,以"陇薯7号"马铃薯为试验对象,进行了不同因素下的跌落冲击试验,分别研究了跌落高度、碰撞材料、马铃薯含水率和跌落方向等因素对马铃薯块茎冲击特性和损伤综合指数的影响,并分析了其损伤规律。研究结果表明碰撞材料、马铃薯跌落高度和含水率对冲击特性影响极显著,而跌落方向不显著;冲击特性参数与损伤指标相关性表明:最大变形量与损伤综合指数之间呈显著正相关(r=0.729,P0.05),恢复系数与损伤综合指数之间呈显著负相关(r=-0.573,P0.05),并得到了恢复系数和最大变形量与损伤综合指数的线性回归模型,决定系数分别为R~2=0.990 7,R~2=0.992 3,加速度峰值与损伤综合指数之间不相关(|r|0.5,P0.05);马铃薯与各碰撞材料相撞时,损伤综合指数与跌落高度之间线性相关,决定系数R~2≥0.951 4。研究结果可对马铃薯在收获过程中碰撞损伤进行评估。     

基于频率和当量损伤系数的井架钢结构损伤识别

诊断井架钢结构损伤的位置和程度是保证其安全服役的关键技术。提出了仅基于测试精度高的低阶频率数据和体现综合损伤的当量损伤系数米识别井架钢结构损伤位置和程度的方法。首先应用两阶频率变化比和频率平方变化比识别损伤位置；其次，引入体现结构整体综合损伤和单元损伤的参数．当量损伤系数，推导了当量损伤系数与频率变化率之间的关系，应用...     

苹果临界跌落高度和损伤脆值的试验研究

目的研究苹果的损伤率与临界损伤脆值的关系。方法利用自制摆锤冲击试验机设计多个高度的苹果跌落试验,分析苹果跌落冲击过程的损伤特性,得到临界跌落高度;在临界跌落高度以上的高度进行跌落试验,得到苹果在跌落过程中的加速度-时间曲线。结果结合试样在不同高度跌落所得的峰值加速度幅值,得到了试样的损伤脆值;根据不同跌落高度下的苹果的损伤体积,得到了苹果在不同损伤率下的损伤脆值。结论研究得到的损伤脆值与损伤率的关系对苹果缓冲包装的改进具有参考意义。     

基于加速度二次协方差矩阵参数变化比法的环境振动下结构损伤识别

在白噪声环境激励下,结构加速度响应的自相关/互相关函数构成一个新的二次协方差（CoC）矩阵,组成这一协方差矩阵的元素经证明是结构模态参数（频率、振型、阻尼）的函数;与提取模态参数的一般损伤识别方法相比,二次协方差矩阵包含结构振动的更多和更高阶模态信息。本文利用结构损伤前和损伤后的二次协方差（CoC）矩阵参数的变化比,对只基于振动输出的、环境振动下的结构进行损伤识别。对一个七层框架结构模型进行了数值模拟,首先对不同噪声程度、不同损伤位置和程度的损伤结构进行损伤定位,再结合模型修正法,对结构损伤程度进行识别,展示了该方法的有效性。     

基于吊索局部振动与神经网络技术的悬索桥损伤定位

基于由吊索局部振动测试构建的吊索张力指标,应用神经网络技术对悬索桥结构损伤位置和程度识别进行了探讨。首先应用经校正的三维有限元模型,对该方法进行了较为详细的数值模拟分析。模拟了多种可能的损伤工况。采用BP网络,以不同损伤程度下基于吊索频率计算的张力指标作为网络的训练与测试输入,由网络的输出向量来指示损伤位置及程度。然后,利用面向健康诊断专门设计制作的悬索桥试验模型,针对个别损伤工况进行了损伤识别的模型试验研究。数值模拟和试验研究均获得较好的损伤识别效果。该方法的突出优点是只用到少量吊索的局部模态的基频,就能获得较好的识别结果。而对少量吊索的局部模态的基频测量要比其它面向损伤检测的测量容易得多。因此,该方法具有重要的实用价值。     

孔口缝合补强复合材料层合板渐进损伤分析

针对孔口缝合补强复合材料层合板,通过有限元软件建立了含孔口缝合补强复合材料的渐进损伤模型。利用该模型预测了不同缝合参数情况下的破坏载荷,数值结果和实验吻合较好,证明了模型的有效性。在拉伸载荷情况下,模拟不同缝合参数下不同铺层的孔边损伤情况,发现不同缝合参数对层合板纤维损伤的影响与铺层角度密切相关。结果显示缝合补强后,层合板的损伤过程有明显的推迟,特别是双缝合情形下推迟的程度尤为显著。     

钢筋混凝土剪力墙基于变形和滞回耗能非线性组合的损伤演化分析

为研究钢筋混凝土结构的损伤演化规律,提出一种基于变形和滞回耗能非线性组合的钢筋混凝土构件损伤模型。通过引入组合参数考虑不同损伤状态下构件变形与滞回耗能的权重,该损伤模型能很好的反映变形和滞回耗能的相互影响,有效评估构件在不同破坏状态下的损伤程度。对4片钢筋混凝土剪力墙的拟静力试验进行数值模拟分析,结果表明:该损伤模型计算的损伤值与试验破坏形态吻合较好,能很好的描述钢筋混凝土剪力墙的损伤演化过程,且能够定量确定构件不同破坏程度的损伤界限;对钢筋混凝土剪力墙进行地震作用下动力时程分析,结果表明,该损伤模型能很好的描述不同峰值加速度作用下剪力墙构件的损伤演化规律,剪力墙损伤在峰值加速度出现时段内发展迅速,并且随着地震强度的增大而增大,损伤值超过限值时构件失效。     

皇冠梨静压力学特性及模拟研究

目的 建立皇冠梨生理特性与力学损伤关系模型,实现果实静压过程的模拟研究。方法 通过材料松弛试验和静态压缩试验,研究果实材料力学特性。使用三维扫描方法辅助建立果实有限元模型,并对果实静载损伤过程进行模拟。结果 使用Maxwell黏弹性材料本构模型,成功模拟了果实流变特性。通过静压试验将所建立的梨果实黏弹性材料模型与传统弹塑性材料模型进行对比,误差降低了7%,从而验证了模拟的准确性。根据von Mises等效应力分布结果进行预测,发现在静载力为161.21 N时梨果实会出现明显损伤。结论 以上研究使用2种材料对静态压缩试验进行仿真模拟,进一步验证了使用数值模拟方法对水果静力学过程模拟的可靠性。为皇冠梨果实机械化采摘、储存包装及加工搬运过程提供了理论依据。     

水晶梨运输包装件振动冲击性能实验研究

针对目前水晶梨在储运过程中的主要包装形式以及造成破损的情况,选择市场较为流通的运输包装件,按照国家测试标准进行定频、扫频、堆码、垂直冲击和跌落实验,研究水晶梨包装件损坏的主要原因。实验证明,包装件的共振频率为25.88 Hz,最大堆码层数为8层,包装件的脆值为90.88g,最大允许跌落高度为450mm。最后评价了包装件在储运过程中对水晶梨的防护能力,并提出了改进建议。     

Relations between fatigue strength and other mechanical properties of metallic materials

The relations between fatigue strength and other mechanical properties especially the tensile strength of metallic materials are reviewed. After analyzing the numerous fatigue data available, the qualitative or quantitative relations between fatigue strength and hardness, strength (tensile strength and yield strength) and toughness (static toughness and impact toughness) are established. Among these relations, the general relation between fatigue strength σ_w and tensile strength σ_b, σ_w = σ_b(C ? P ? σ_b), where C and P are parameters, (hereafter, the general fatigue formula) can well predict the fatigue strength with increasing the tensile strength in a wide range for many materials such as conventional metallic materials, newly developed materials and engineering components. On the basis of the experimental results of many materials, the fatigue damage mechanism, especially for high‐strength steels, is proposed. It is suggested that the general fatigue formula can provide a new clue to predict the fatigue strength and design the materials by adjusting material parameters P and C adequately.     

A new creep damage assessment method for metallic material under variable load conditions at elevated temperature

It is significant for structural design and maintenance to assess behaviour and life under varying load conditions. For structures operating in high‐temperature environments, creep is one mechanism responsible for material failures. In this paper, different damage accumulation rules were reviewed, and a new creep damage assessment method was proposed based on the creep damage tolerance parameter λ and load factor Φ. By introducing the creep damage tolerance parameter λ and the minimum creep rate, the loading process and creep behaviour of the material are taken into account in a damage assessment. The parameters in the model can be obtained by the simple variable load creep test, and the remaining life and strain can be predicted using uniaxial creep test data. To analyse the applicability and accuracy of this new model, the strain histories, the life of step load, and the constant load creep from experiments on a titanium alloy at 500°C were obtained, and the prediction results of the novel and previous methods were carefully investigated.     

After-ripening of fruits adjusted by ethylene-generating agents

A simple way of after-ripening for pears and kiwi fruits was studied using ethylene-generating agents and films for packaging. A method that requires no special facility or apparatus. For the generation of ethylene, two agents were used with different gas-generating characteristics (A, zeolite; B, powder ethanol with catalyser), and the fruits were packaged either in a 20-kg harvesting container or a unit pack of 3.5 kg each. In the combination of agent A and the harvesting container, pears were treated with ethylene for 2 days (C₂H₄, 3250 or 1700 ppm), and kiwi fruits for one day (C₂H₄. 2050 or 750 ppm). Thus the treated fruits were ripened faster than those untreated, i.e. about 10 days earlier for the pears and 40–50 days earlier for the kiwi fruits. Using Agent B, kiwi fruits were stored/packaged in EVA30 and PE30 films (C₂H₄, 350 or 30 ppm). The fruits were ripened in several days, but gas damage was evident in the PE30 packagings. In addition, changes in fruit respiration were studied, and the effects of treatment with ethylene also were confirmed from the physiological point of view.     

基于代理模型的复合材料加筋壁板分层损伤定量监测方法

通过建立损伤指数与分层损伤参数间的定量关系,对复合材料加筋壁板分层损伤进行准确定量监测,提出了一种基于代理模型的分层损伤定量监测方法。该方法包括代理模型的建立和逆求解两个过程,通过插值拟合方法建立表征分层损伤参数与损伤指数间定量关系的多项式代理模型;采用损伤概率成像算法获得相对距离和损伤指数,将其代入代理模型中,得到所对应的分层损伤面积;实现对分层损伤进行定量评估的目的。通过一个复合材料加筋壁板分层损伤的定量监测实验,对所提方法的有效性进行了验证。结果表明:基于代理模型的复合材料分层损伤定量监测方法可以实现对分层损伤位置的准确定位,定位误差低于6%;且可实现对分层面积的准确定量评估,定量误差不超过5%。      

The life evaluation by linear cumulative damage rule for cold dwell fatigue of Ti-6Al-4V alloy

Low cycle fatigue (LCF) life at ambient temperature of Ti alloys is well known to decrease with stress dwell. This phenomenon, called cold dwell fatigue (CDF), is influenced by the peak stress, dwell time, and microstructure. For this study, the CDF life was evaluated by the linear cumulative damage rule. The influence of test conditions and microstructure on the linear cumulative damage rule was also verified. By the linear cumulative damage rule, when creep damage is calculated using the time exhaustion rule, theCDF damage was evaluated by the inequality of D_Total = (D_F, D_C) ≤ (0.01, 10^?6). However, the CDF damage can be evaluated in the range of D_Total = 0.6–1.2 when creep damage was calculated using the ductile exhaustion rule. Results indicate that the evaluation was almost independent of the dwell time, peak stress, and microstructure, so it is also a versatile method for evaluating CDF responses.     

Effect of annealing temperature on electrical characteristics of ruthenium-based Schottky contacts on n-type GaN

The electrical properties of ruthenium (Ru) and ruthenium/gold (Ru/Au) Schottky contacts on n-type GaN are investigated as a function of annealing temperature by current–voltage (I–V) and capacitance–voltage (C–V) techniques. The Schottky barrier height of as-deposited Ru/n-GaN is found to be 0.88 eV (I–V) and 1.10 eV (C–V) respectively. However, after annealing at 500°C for 1 min in the nitrogen ambient, the decrease in barrier height is quite considerable and found to be 0.80 eV (I–V) and 0.86 eV (C–V). In the case of Ru/Au Schottky diode the measured barrier height is 0.75 eV (I–V) and 0.93 eV (C–V). In contrast to the Ru contacts, it is interesting to note that the barrier height of Ru/Au depends on the annealing temperature. Annealing at 300°C improves the barrier height and the corresponding values are 0.99 and 1.34 eV. Further increase in annealing temperature decreases the barrier height and the respective values are 0.72 and 1.08 eV at 500°C. From the above observations, it is clear that the electrical properties of annealed Ru/Au contacts are improved compared to the as-deposited films. However, Ru Schottky contacts exhibit a kind of thermal stability during annealing.