小冲杆试验方法研究进展及存在的问题

SP小冲杆试验法在力学测试中得到了广泛的发展和应用.用SP试验法测得的小试样的载荷-位移-试样厚度变化曲线,通过类比分析以及半解析相结合的方法可以计算材料的特征常数:屈服极限、强度极限、断裂韧性、转变温度和蠕变特性,并且从大量的试验数据、理论模型和有限元计算模型来看,SP试验法测得的结果与相应的大尺寸标准力学测试方法得到的数据有着直接的对应和转换关系.介绍了该试验方法的试验技术、分析方法、研究进展及其应用,并分析了该试验方法目前所存在的一些问题.     

用于获取延性材料力学性能的锥-小冲杆试验新方法与应用

对于均匀、各向同性、幂律硬化的金属材料,以锥形端头小冲杆对试样圆面中心法向施加压载荷,提出基于能量密度等效的,用于描述试样几何尺寸、材料本构关系参数、载荷和位移之间关系的锥-小冲杆试验（cone small punch test, C-SPT）载荷-位移模型,并提出获取材料应力-应变关系和力学性能指标的锥-小冲杆试验新方法。通过有限元分析不同弹性模量、屈服强度和硬化指数的100种预设材料进行新方法的数值验证,及对3种金属材料完成CSPT。结果表明：由新方法预测的应力-应变关系与有限元分析预设曲线和传统单轴拉伸试验结果吻合良好,此外,由新方法获得的抗拉强度与单轴拉伸试验结果误差较小。     

基于西门子S7-200系列PLC的小冲杆试验机自动化改造

介绍了西门子S7-200系列PLC在小冲杆试验机系统中的运用,实现了试验机的自动化改造,有效地简化了试验步骤。并且使用Visual Basic6．0软件实现了PLC与PC机之间的串行通讯,实现了对试验数据自动采集、显示以及相关计算等功能。     

木塑复合材料蠕变特性及预测方法的研究进展

木塑复合材料(WPCs)已广泛应用于建筑外墙板、户外铺板、室内装饰、园林景观、汽车内饰等非承重结构材料领域,但由于线型或支链型热塑性聚合物固有的粘弹特性决定了 WPCs在受到长期力载荷时易发生蠕变变形,严重影响其作为承重结构材使用.因此抗蠕变是木塑产业界面临的重大技术瓶颈,也是学术界关注的核心科学问题.为更好地了解并改...     

实用断裂试验方法的意义与内容（一）

为了在材料性能检测中普遍、持久地应用断裂试验,推荐一种延性材料断裂韧性实用测试方法。该实用测试方法包括侧切三点弯曲试件、测量δｃ的两点位移法和测量ＪＩＣ的位称计法。该方法具有科学合理、通谷易懂、准确可靠、简便快捷、费用低廉等显著特点,适合普遍推广应用。     

SP试验法的研究进展

详细阐述了Small Punch Test(SP)方法的发展及研究现状,系统介绍了该方法的特点及应用该方法测试各种力学性能的进展,展望了其发展前景.     

接近液氦温度的简易却贝冲击试验法

提出了在低于5K温度下检验材料冲击性能的简易试验方法。     

西安小雁塔结构模型振动台试验研究

以西安小雁塔结构为原型,对其缩尺比例为1/8的砖塔模型进行了振动台试验。模型采用旧青砖和糯米汁灰土浆作为砌筑材料以还原古代砖塔的营造特点,试验分析了结构模型在多遇以及罕遇地震烈度水平下的损伤状况、加速度响应,位移响应和层间剪力分布,并通过分析各层测点在白噪声激励下的频率响应函数,得到了结构动力特性及其变化规律。试验结果表明:模型结构鞭鞘效应明显,损伤主要集中在顶部,其破坏形态与类似结构的实际震害特点一致;在不同的地震波作用下结构响应不尽相同,其加速度位移与结构当前频率、地震波频谱特性息息相关;随着地震波加速度峰值的增大,模型一阶频率减小了27.4%,阻尼增大为2.55倍,地震加速度放大系数减小;在8度多遇地震作用下,模型结构的顶层层间位移角达到1/116,结构已达到严重破坏状态,对处于高设防烈度地区的类似古塔应采取保护措施。     

中小煤矿存在的问题及采煤方法探讨

对于中小煤矿来说,由于煤层赋存不稳定、矿井技术力量薄弱、职工素质差等原因,很多煤矿仍在使用非正规采煤法,因此,按防突的要求合理选择巷道布置和正规采煤方法就显得尤其重要。     

一种小流量旋涡泵的汽蚀性能试验研究

对一种小流量旋涡泵的汽蚀性能进行了理论分析及试验研究.在试验中利用了LabVIEW软件进行数据的实时采集、存储,并用Access及Excel进行数据的记录处理,使用了精度较高的传感器并进行软件及硬件滤波,以克服流体脉动及随机因素造成的误差,使试验精度提高.提供了一份小流量旋涡泵汽蚀试验数据,可为小流量旋涡泵汽蚀性能的研究提供参考.     

Analysis of different techniques for obtaining pre-cracked/notched small punch test specimens

Nowadays, there are standards for determining the mechanical and fracture properties of a material. However, these standards require a sufficient amount of material to be tested, something that is not always possible or convenient. In those cases where there is not enough material for conducting conventional tests to determine these properties of the material analyzed, there are now several non-standard tests that will achieve this purpose. One of them is the small punch test (SPT), which basically consists of deforming a miniature specimen using a high-strength punch, while the sides of the specimen are clamped between two dies. One of the greatest challenges at present is to obtain the fracture properties of a material from this type of test using pre-cracked specimens. To achieve this initial crack in the SPT specimen prior to fracture testing, there are two techniques which are mainly being used at present. The first one uses high-precision micromachining (HPM), while the second relies on laser-induced micromachining (LIM). The main objective of this paper is to analyze the differences between these two techniques, taking into account the shape of the pre-crack obtained and the stress distribution at the pre-crack tip during the test. In this way, it is possible to determine which of them is the most appropriate for estimating the fracture properties of the material used.     

Derivation of ductile fracture resistance by use of small punch specimens

Conventional fracture mechanics cannot address the influences of stress triaxiality since the assumption of geometry independence is valid only in limited conditions. Various local approaches have been proposed to investigate the material’s fracture behaviours covering a broad range of loading and flaw shapes. However, unfortunately, standard test specimens have been difficult to obtain from operating facilities. This paper investigates the characterization of ductile fracture resistance (J–R) curves by the small punch (SP) testing technique in conjunction with finite element analyses incorporating well-known damage models. In this context, basically, standard tensile tests and SP tests using tiny specimens are carried out. Furthermore, micro-mechanical parameters constituting the Gurson–Tvergaard–Needleman and Rousselier models are calibrated for typical nuclear materials based on experimental and estimated load–displacement data of their miniaturized specimens. Then, the J–R curves of larger (compact tension) as well as standard 1T-CT specimens are predicted by detailed finite element analyses employing the calibrated parameters. Finally, the estimated J–R curves are validated by fracture toughness tests using the standard CT specimens. The estimated results suggested confidence in the use of the proposed method for ductile crack growth evaluation.     

Determination of deformation and failure properties of ductile materials by means of the small punch test and neural networks

This paper describes an approach to identify plastic deformation and failure properties of ductile materials. The experimental method of the small punch test is used to determine the material response under loading. The resulting load displacement curve is transferred to a neural network, which was trained using load displacement curves generated by finite element simulations of the small punch test and the corresponding material parameters. The simulated material behavior of the specimen is based on the ductile elastoplastic damage theory of Gurson, Tvergaard and Needleman. During a training process the neural network generates an approximated function for the inverse problem relating the material parameters to the shape of the load displacement curve of the small punch test. This technique was tested for three different materials (ductile steels). The identified parameters are verified by testing and simulating notched tensile specimens.     

Identification of ductile damage and fracture parameters from the small punch test using neural networks

This paper presents a method for the identification of deformation, damage and fracture properties of ductile materials. The small punch test is used to obtain the material response under loading. The resulting load displacement curve contains information about the deformation and failure behavior of the tested material. The finite element method is used to compute the load displacement curve depending on the parameters of the Gurson-Tvergaard-Needleman damage law. Via a systematic variation of the material parameters a data base is built up, which is used to train neural networks. This neural network can be used to predict the load displacement curve of the SPT for a given material parameter set. The identification of the material parameters is done by using a conjugate directions algorithm, which minimizes the error between an experimental load displacement curve and one predicted by the network function. The identified material parameters are validated by independent tests on notched tensile specimens. Furthermore, these parameters can be used to compute the crack growth in fracture specimens, which finally leads to a prediction of classical fracture toughness parameters.     

Polymer pre-notched small punch specimens to evaluate the essential work of fracture (EWF) parameters

Standardized deeply double edge notched tensile specimens (DDEN-T) have been usually used to assess fracture properties in thin polymer plates under plane stress conditions. The methodology is based on a multi specimen technique and is well known as the essential work of fracture (EWF) method. In some special circumstances these standard specimens cannot be machined as could be the case if the material is limited. A possible solution proposed in this paper could be the use of pre-notched small punch test specimens, in which the aim is to establish the feasibility of using pre-notched SPT specimens for evaluating the essential work of fracture parameters. The results obtained with these miniature specimens have been compared with those obtained from standard DDEN-T specimens.     

Inverse determination of the elastoplastic and damage parameters on small punch tests

The small punch test (SPT) is very useful in those situations where it is necessary to use small volumes of material. The aim of this paper is to create and validate a methodology for the determination of the mechanical and damage properties of steels from the load-displacement curve obtained by means of SPTs. This methodology is based on the inverse method, the design of experiments, the polynomial curve adjustment and the evolutionary multi-objective optimization, and also allows simulating the SPTs. In order to validate the proposed methodology, the numerical results have been compared with experimental results obtained by means of normalized tests. Two dimensional axisymmetric and three-dimensional simulations have been performed in order to allow the analysis of isotropic and anisotropic materials, respectively.     

Determination of creep properties of P91 by small punch testing

Abstract

Small punch creep testing was conducted to determine creep properties of P91 at 873 K. The procedure followed the European Code of Practice for Small Punch Tests. Results of small punch creep test and finite element analysis were compared and discussed. Based on the results, a practical method was proposed to determine the parameters of Norton creep law more conveniently for material which obey this law. The validity of the proposed method was verified and it is shown that the parameters of the Norton creep law can be determined from only one experimental curve directly.     

Introduction of a new notched specimen geometry to determine fracture properties by small punch testing

The small punch (SP) testing technique can be used to assess fracture properties from a very small volume of material. However, the correlation of fracture parameters obtained from SP testing with those produced using standard methods is non-trivial, not only due to the size effect, but also due to the absence of a notch in most existing types of SP specimens. In the present study, a novel SP specimen design is proposed, with a sharp circular notch, leading to the development of a near plane strain condition during the SP test. The new geometry is examined through SP testing of P91 steel, as well as finite element analysis. Optical and scanning electron microscopy is used to study the crack propagation from the notch tip in both ductile and brittle fracture modes.     

Assessment of stress corrosion cracking susceptibility by a small punch test

The object of this study is to establish a new test method for evaluating stress corrosion cracking (SCC) susceptibility of high-strength steel using a small punch (SP) test and acoustic emission (AE). A miniaturized specimen (10 × 10 × 0.5 mm) is adopted for SCC evaluation. The experiments are conducted at various loading rates and at various orientations of the specimen. The cumulative average amplitude of the AE signal per unit equivalent fracture strain ( ε _qf ) increases as the SCC susceptibility increases. Through the load–displacement behaviour, the fracture energy ( E _SP ), the SEM fractographs, and the correlation between the SCC susceptibility and the AE characteristics, it is proved that the small punch test method combined with AE measurements is a useful method to evaluate the SCC susceptibility of high-strength steel.