基于弯曲刚度最大分层临界载荷的层压板局部屈曲预测

提出了一种预测含特定分层损伤层压板发生局部屈曲时整体应变的方法。认为含分层子板的局部屈曲载荷由其弯曲刚度最大的分层决定, 因而含有相同最大弯曲刚度分层的不同子板具有相同的屈曲载荷。在已知弯曲刚度最大分层的屈曲载荷的情况下, 根据层压板的轴向刚度公式, 计算出发生局部屈曲时弯曲刚度最大的分层与完好的基板分别承受的载荷, 即得到总载荷, 进而得到层压板的整体应变。用ABAQUS有限元分析软件建立含分层损伤的层压板模型, 使用准静态加载进行了多种分层深度和分层位置下的局部屈曲仿真, 所得局部屈曲载荷符合上述推论。用所提方法预测发生局部屈曲时的整体应变, 结果与有限元结果吻合较好, 此方法可用于建立分层参数识别的参照样本库。     

基于弯曲刚度最大分层临界载荷的层压板局部屈曲预测

提出了一种预测含特定分层损伤层压板发生局部屈曲时整体应变的方法.认为含分层子板的局部屈曲载荷由其弯曲刚度最大的分层决定,因而含有相同最大弯曲刚度分层的不同子板具有相同的屈曲载荷.在已知弯曲刚度最大分层的屈曲载荷的情况下,根据层压板的轴向刚度公式,计算出发生局部屈曲时弯曲刚度最大的分层与完好的基板分别承受的载荷,即得到总载荷,进而得到层压板的整体应变.用ABAQUS有限元分析软件建立含分层损伤的层压板模型,使用准静态加载进行了多种分层深度和分层位置下的局部屈曲仿真,所得局部屈曲载荷符合上述推论.用所提方法预测发生局部屈曲时的整体应变,结果与有限元结果吻合较好,此方法可用于建立分层参数识别的参照样本库.     

2D-SiC/SiC复合材料拉伸加卸载行为

为了研究国产2D-SiC/SiC复合材料的拉伸损伤行为以及低周循环载荷作用下的力学性能,通过试验和建立加卸载细观力学模型,对其拉伸加卸载行为进行了探讨。建立了单向连续纤维增强陶瓷基复合材料加卸载细观力学模型,得到了初始加载、卸载和重新加载时的应力-应变关系;利用断裂统计方法得到了基体裂纹数随应力变化的关系和复合材料失效判断条件。经过应力转化,将该模型应用于国产二维编织SiC/SiC复合材料。对单向加载试件,采用正交试验方法和最小二乘法得到基体Weibull模量和界面剪切阻力,通过控制材料失效强度与试验结果一致,得到纤维Weibull模量。由上述参数确定的2D-SiC/SiC复合材料拉伸循环加卸载应力-应变曲线与实测曲线吻合很好。通过Matlab编程得到2D-SiC/SiC复合材料单向加载时基体开裂过程图。结果表明,2D-SiC/SiC复合材料失效时,基体裂纹分布相对比较均匀;基体裂纹数随应力单调增加,未出现持平段,表明材料失效时,基体裂纹还没有达到饱和。     

燃气环境中碳/碳复合材料循环载荷下的损伤机理

将覆有SiC涂层的C/C材料置于甲烷燃气风洞中进行了循环载荷试验.应力-应变迟滞回环面积和棘轮应变的变化同时表明材料受到的损伤大部分发生在前50次循环,之后随着循环次数的增加,损伤的积累逐渐趋于稳定状态.材料在风洞环境下受到氧化,呈现出层状氧化形貌,这是由于碳纤维和碳基体之间不同的氧化速率所致.经过循环加载而未断裂的试样的残余强度比原始强度降低了19%,仅遭受氧化而未循环加载的试样强度相对原始值降低了38%.对试样的横截面微结构进行观察发现材料受到循环载荷后纤维/基体界面发生脱粘现象.拉伸实验中的实时声发射信号表明,只有当拉伸应力大于材料遭受的最大历史载荷时,试样才会发生明显的损伤.     

复合材料单向层合板损伤失效试验研究

对T300/BMP-316单向层合板静载及疲劳加载各主方向损伤失效进行了试验研究, 为建立该材料各主方向疲劳加载剩余刚度退化表达式及剩余强度退化表达式提供了依据。同时, 获得了该材料剪切非线性因子, 给出了面内剪切疲劳加载试验循环过程中剪切刚度计算公式, 使用渗透剂增强的X射线图像技术对试样静载及疲劳破坏损伤状态进行了无损检测, 并对损伤失效机理形式进行了分析探讨。试验表明, 层合板结构应力分析中考虑材料剪切应力-应变的非线性效应是非常必要的。      

直升机尾减速器机匣疲劳试验方法研究

根据减速器机匣疲劳损伤应力循环的动、静应力包罗线方法确定了疲劳试验加载方案;根据设计载荷谱或飞行实测,确定各载荷作用点的状态载荷并编制了疲劳试验谱;根据减速器机匣的受力形式,完成减速器机匣疲劳试验装置的设计。结果表明,该试验装置既可以考虑高频动载荷的影响,又能简化疲劳试验的加载程序,明显缩短了疲劳试验的周期。     

加载载荷对ADB610钢疲劳裂纹扩展性能的影响研究

针对ADB610新型低碳贝氏体钢,采取紧凑拉伸试样、恒幅加载方式,在应力比为0.1时进行3种不同加载载荷下多试样的疲劳裂纹扩展试验,并测出裂纹扩展长度a和循环寿命N的a-N试验数据。然后采取七点递增多项式法对a-N试验数据拟合计算疲劳裂纹扩展速率。结果表明,加载载荷较小时,ADB610钢循环寿命较长;在疲劳裂纹扩展的初始阶段,加载载荷小的疲劳裂纹扩展速率相对较慢,但随着疲劳裂纹逐渐扩展,加载载荷小的疲劳裂纹扩展速率反而更大一些。     

杨木静动态压缩本构模型研究

目的 以杨木为研究对象,研究其静动态压缩载荷作用下应力-应变曲线的变化特征,建立适合的本构模型,并对其进行描述。方法 对杨木试件进行静动态压缩加载试验,分析静动态压缩载荷作用下杨木应力-应变曲线的变化特征,构建适用于静动态压缩载荷作用下杨木的本构模型。结果 静态压缩加载杨木的应力-应变曲线分为线弹性阶段、屈服阶段和密实化阶段等3个部分,动态压缩加载杨木的应力-应变曲线分为线弹性阶段和屈服阶段等2个部分;静态压缩加载时,杨木轴向屈服应力最大,分别是径向和弦向的5.70倍和7.75倍;动态压缩加载时,当应变率从400 s-1增加到1000 s-1时,径向、弦向和轴向的屈服应力分别增加了1.51,1.59,3.12倍,杨木的屈服应力具有应变率敏感性;采用包含应变率影响的本构方程来描述杨木在静动态压缩载荷作用下的本构关系是比较合适的。结论 杨木是一种应变率敏感材料,静动态压缩载荷作用下杨木的应力-应变曲线均表现出多孔材料的特征,将多孔材料本构模型应用于木材是可行的。     

拉-压循环加载下铝合金疲劳裂纹扩展的压载荷效应研究

应用弹塑性有限元方法与增量塑性损伤理论指出疲劳裂纹扩展的压载荷效应是裂纹尖端塑性损伤的结果, 建立了在拉-压循环加载下铝合金疲劳裂纹扩展速率的双参数预报模型, 对LY12-M 高强铝合金MT 试件在应力比R=0、-0.5、-1、-2 进行了疲劳裂纹扩展实验。结果表明:当最大应力强度因子K_max相同时, 恒幅拉压加载(应力比R<0)的疲劳裂纹扩展速率明显高于恒幅拉拉加载(应力比R=0)的情况, 拉-压循环载荷的压载荷部分对疲劳裂纹扩展速率具有促进作用。该文得出的LY12-M 铝合金在拉-压循环加载下的疲劳裂纹扩展速率预报模型与实验结果符合较好。     

TiNi形状记忆合金丝在约束态热循环后的力学特性

研究了TiNi形状记忆合金丝在约束态热循环后的应力-应变特性.结果表明,如果停止加热并加载,或者在母相状态下冷却但是尚未发生正相变时加载,加载应力-应变曲线首先呈线弹性关系,然后才出现应力平台.如果在冷却过程中发生正相变的时候停止冷却并加载,则加载应力-应变曲线只出现应力平台.与之相似,如果在约束态冷却过程中停止冷却并卸载,卸载应力-应变曲线首先呈线弹性关系,然后才出现应力平台.如果在加热过程中停止加热并卸载,则卸载应力-应变曲线立即出现应力平台.     

The Performance of Three-Dimensional Strain Rosettes Evaluated when Embedded into a Sphere

Abstract:  Two spheres were manufactured, each containing planes of embedded strain gauges that were arranged so that individual gauge readings could be combined in a variety of ways to calculate the least squares strain tensor. Each sphere was tested by loading along its axis of symmetry. It was found that the particular pattern of rosette chosen produced satisfactory predictions of the orthogonal strains but minor off-axis gauge misalignments combined with the matrix operations in the least squares strain tensor led to misleading forecasts of the shearing strains. The method of manufacture used to embed the gauges was largely responsible for these errors. The investigation confirmed that three-dimensional strain rosettes should be made from square plugs and the direction cosines measured on the plug prior to embedment in the model.     

The Measurement of Stresses in Objects

Relations for calculating the stresses in objects from the results of measurements in them of the strains for complex forms of loading are presented. __________ Translated from Izmeritel'naya Tekhnika, No. 9, pp. 56–59, September, 2005.     

A Novel Strain Sensor for Reinforced Concrete Structures

Abstract:  Reinforced concrete (RC) is the most commonly used structural material in civil engineering applications. RC structures have long-term service lives under normal loading conditions; however, overload caused by misuse or statistically remote events such as earthquakes may create damages that, if not detected in time, may eventually cause failure. Hence, it is important to monitor RC structures to take necessary precautions and save human lives. A long-gauge strain (LGS) sensor has been developed to monitor these structures. While it has been developed mainly with concrete applications in mind, the new sensor can also be used in a variety of applications, including measuring strains in pipelines, steel structures, and the like. The proposed sensor system has a very low cost compared with the commercially available competing systems. Prototypes of the proposed strain sensors have been built and calibrated. Test results prove the accuracy, repeatability and reliability of the proposed strain sensor. When the LGS sensor was incorporated into a concrete beam there was very good agreement between the experimental measurement of strain using the LGS sensor when compared with two strain-gauged parallel steel rebars in the same concrete beam.     

A Probabilistic Evaluation of the Least Squares Strain Tensor Derived from a Three-Dimensional Modular Strain Rosette Using the Monte-Carlo Technique

Abstract:  Strain gradients give rise to a number of problems in the field of embedded three-dimensional strain measurement. In order to avoid these problems a modular type three-dimensional strain rosette was embedded into known strain fields and the data from the individual gauges compared with theoretical predictions. Finally, the least squares strain tensor was predicted from experimental data analysed using the Monte-Carlo technique and the theoretical results forecast from finite element data taking into account the mechanical properties of the carrier, plug and prismatic bar. Some of the experimental results were found to correlate well with the theoretical values but some values in the least squares strain tensor, in particular under compression and torsional loading, departed considerably from the theoretical values. It was found that the effect of the measurement errors in the individual gauges combined with the matrix operations in the least squares strain tensor were responsible for biasing the resultant tensor data. However, the modular technique provided a solution to the problem of strain gradients.     

Ni－Mo系50℃自补偿应变电阻合金性能研究

对Ｎｉ－Ｍｏ系应变电阻合金成份、加工工艺、合金性能进行了研究。特别对典型合金的Φ０．０３ｍｍ细丝应变电阻性能及制片性能进行了详细地研究。本研究最终为５００℃自补偿应变测量，提供了良好的合金。     

Analysis of the Plastic Deformation Micrononuniformity Effect on the Strain Resistance of the Metal

A simplified model of micrononuniform deformation of the metal at a constant strain rate (uniaxial macrouniform stress state) is presented. The account of a temperature increase upon plastic strain and its localization due to the deformation micrononuniformity is shown to give a qualitative explanation of impact indentation results that point to a decrease in dynamic hardness over the range of high strain rates. Calculation results obtained with this model demonstrated that the localization effect was growing with strain rates and characteristic localized flow layer sizes. At small strains of the material, containing thin localized flow layers, the deformation micro- nonuniformity effect on strain resistance is insignificant.     

Strain Measures for Rigid Crushable Foam in Uniaxial Compression

Abstract:  Progressive collapse deformation mechanisms in Rohacell-51WF foam during uniaxial compression has been studied. Measures of a macroscopic engineering strain are identified. The elastic and plastic parts of a macroscopic engineering strain can be predicted by using the compression failure strain, lock-up strain, and time dependent elastic and plastic parts of lock-up strain, which are material parameters. Identification of strain measures in a uniaxial compression test is essential to get material parameters for an elastoplastic model. The viscoelastic recovery property of Rohacell-51WF foam is also described.     

Prediction Models on Distribution of Inherent Strains in T Type Welding Structure

A fundamental theory for the analysis of residual welding stresses and deformation based on the inherent strain distribution along the welded joint is introduced. The method of predicting maximum hardness Hv(y, z) and maximum inherent strain gmax is given     

A Comparison of Various Patterns of Three‐Dimensional Strain Rosettes

Abstract: The strain tensor, principal strains and precision of the estimates of these values are derived for a range of different layouts of three‐dimensional strain rosettes. These values are based on the Monte Carlo technique applied to experimental work which was carried out on transducers tested in different laboratories. The estimates of precision are determined theoretically and compared with results based on experimental findings. A new design of a miniature tri‐rectangular tetrahedral rosette was manufactured and tested. Results suggest that this transducer does not perform as well as the rectangular patterns.