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.     

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。     

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.     

公路工程试验检测存在的问题及措施

工程试验检测工作是公路工程施工技术管理中的一个重要环节,也是公路工程质量控制和竣工验收评定工作中不可缺少的一个主要部分。通过试验检测能充分的利用当地原材料,迅速推广新技术、新材料、新工艺;能用定量的方法科学的评定各种材料和构件的质量;合理的控制并科学地评定工程质量。本文分析了公路工程试验检测工作的重要性及目前公路工程试验检测工作中存在的主要问题,针对存在的问题,提出了加强公路工程试验检测工作的措施。     

工地试验检测存在的问题及措施分析

建筑工程质量控制的主要手段之一是工地试验检测。但是,随着建筑市场的蓬勃发展,在工地试验检测工作中出现了许多问题,已严重不适应当前建筑市场的需求,工地试验检测方法工艺急需改进。我参与工地试验检测工作已有十几年了,现结合当前工地试验检测工作中存在较多的问题进行了分析,并提出了相应的改进措施。     

Determination of creep behaviour of Ti60 alloy by small punch creep test

The small punch (SP) creep test has distinct advantages in the creep property assessment of materials at elevated temperatures. However, there are few creep properties of Ti alloys obtained by the SP creep test in the current literature. In this paper, the SP creep behaviour of Ti60 alloy has been evaluated under various loads in the range 550–800 N over a temperature range 873–973 K. The SP creep curves obviously indicated the primary, secondary and tertiary stages of creep. The test results have been compared with those of conventional creep tests. The European Code of Practice (CoP) for Small Punch Testing, Dorn equation and Monkman–Grant relationship have also been used to analyse the results of the SP creep tests. The ratio of load of the SP creep tests to equivalent stress of conventional creep tests, the load exponent value of steady deflection rate and activation energy for creep deformation were estimated from the SP creep tests. In conclusion, it was found that dislocation creep may be the main mechanism that dominates the SP creep deformation of Ti60 alloy in the range of load and temperature.     

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.     

Development of a new methodology for estimating the CTOD of structural steels using the small punch test

The small punch test (SPT) is very convenient for estimating tensile mechanical properties, being the estimation of fracture toughness still a controversial subject of debate. One of the new strategies developed is the use of notched specimens. In this paper, two different grades of CrMoV steels were employed to analyse the evolution of the notch mouth opening displacement of the small punch sample (δSPT). Complete and interrupted tests were performed on specimens with longitudinal non-through notches with a notch length to thickness ratio of 0.3. A numerical model was also developed for corroborating the experimental results. A material-independent relationship between δ_SPT and the punch displacement (d) was found: δ_SPT = 0.217d. Since crack length measurement is not possible on SPT samples, the value of δ_SPT at crack growth onset (δ_{SPT_ini}) was used for comparison with the CTOD values for crack initiation in the standard tests (δ_ini). Crack growth onset in the SPT specimens was verified by observation after splitting them in two halves, as well as comparing the numerical curves (without damage model) and the experimental ones. Larger values have been obtained by means of the SPT, due to the lower constraint of the test. However, the developed methodology seems to be suitable when dealing with ductile steels, although other different materials are needed to be tested.     

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.     

Experimental study of remaining creep life of SA-304L stainless steel using small punch creep test

In this paper, the remaining creep life of SA-304L stainless steel at elevated temperatures is studied. The small punch creep tests (SPCT) were performed on SA-304L virgin and aged materials at constant loads. Times to fracture and the minimum deflection rate in SPCTs were recorded, and the time-temperature parametric analysis was performed, based on experimental results. The constants of the Larson–Miller parameter and the Monkman–Grant relationship were obtained for different consumed creep life ratios, and eventually the equations were established to explain the variation of constants of the Larson–Miller parameter and the Monkman-Grant relationship with respect to the consumed creep life ratio.     

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.     

New approach to determine uniaxial creep properties from small punch creep curves

A key issue in the small punch creep test (SPC) is to determine the equivalent stress that results in the same time to rupture in a uniaxial creep test (UAC). A new approach is proposed based on formulas between the ratio of force in SPC to stress in UAC and the deflection at the minimum deflection rate. Another formula is defined between the minimum deflection rate and the minimum strain rate. In both cases, they were created from a large experimental data pool of high temperature creep-resistant steels. The predicted Norton law and the rupture time dependence on stress are in good agreement with the experimental UAC results. In all cases, the predictions using the present approach are much better than those based on Chakrabarty membrane stretch model.