仪器化压痕技术测试拉伸性能的重复性和准确性

采用新型便携式压痕仪和传统万能拉伸试验机两种测试仪器,对相同种类和尺寸的碳钢试块进行了拉伸性能测试,测试试块的屈服强度和抗拉强度,以验证仪器化压痕试验结果的重复性和准确性。结果表明:仪器化压痕技术测试屈服强度和抗拉强度的重复性较好,准确性较高;不同于现有的破坏性测试设备和评估方法,压痕系统使用无损害、经济和高效的仪器化压痕测试方法,可以通过评估从局部区域的纳米尺度到现有工业设施的宏观属性来提供可靠的解决方案。     

仪器化压痕法在在役设备检测中的应用

仪器化压痕技术(IIT)是一种新型的检测在役设备弹性模量、屈服强度、抗拉强度和硬度等力学性能的技术。IIT是通过压头在材料表面下压得到载荷-深度曲线,然后通过分析载荷-深度曲线得到材料的各项力学性能。通过该技术可以实现对在役设备的非破坏力学性能检测。     

连续球压痕法测试钢管应变时效后拉伸强度的变化

以不同状态的20钢国产新管和断裂管为研究对象,采用连续球压痕与常规拉伸试验相对比的方法,对不同状态钢管的屈服强度和抗拉强度进行了测试。结果表明:连续球压痕法能够准确反映应变时效前后20钢管的力学性能变化,可以对不同状态的20钢管的力学性能进行无损测试。     

仪器化压痕法单次加载数据绘制应力-应变曲线计算拉伸试验结果的方法初探

采用压痕仪自动采集的位移数据减去压痕仪的弹性变形量得到压痕深度,进而计算出压痕直径,再根据TABOR提出的关于压痕方法测试拉伸性能的系列关系式,计算出真应力、工程应力和应变,绘制出压痕法的连续应力-应变曲线和lg W-lg d曲线,根据两种曲线计算出抗拉强度、屈服强度和应变硬化指数(n值)。实测数据显示压痕法的连续应力-应变曲线与拉伸法的应力-应变曲线存在显著差异。对压痕法测得的抗拉强度、屈服强度和n值的测量不确定度进行了详细分析,结果表明:抗拉强度的测量不确定度小于抗拉强度值的10%,而n值的相对测量不确定度显著大于抗拉强度的相对测量不确定度,目前尚未找到可靠评估屈服强度测量不确定度的方法。     

陶瓷材料压痕韧性的统计性质

采用直接压痕法测定了钠钙硅酸盐玻璃和一种ＴｉＣ 颗粒增强Ａｌ_２Ｏ_３复合材料的断裂韧性．研究表明,在同一压痕压制荷载下测得的同一种材料的压痕韧性呈现出较大离散性,可以采用Ｗｅｉｂｕｌｌ分布加以较好地描述．对两种材料的试验数据的对比分析指出,压痕韧性测试值的离散性反映了材料显微结构的不均匀性对材料局部裂纹扩展阻力的影响．基于这一分析,本文建议采用直接压痕法测定材料断裂韧性时,应尽可能增大试验量,从而对压痕韧性测试结果的统计性质作出完整描述．     

用连续球压痕法评价钢断裂韧度

作为一种无损力学性能测试方法,球压痕法可以用来评价在役设备材料性能。为了探究球压痕法获得断裂韧度的可行性,本文对五种材料进行连续球压痕试验和三点弯试验,并将两种试验方法所得的断裂韧度KJC进行比较。结果表明,球压痕试验和三点弯试验获得的断裂韧度偏差在10%以内,可以满足一般性的工程应用要求。同时,用三维表面测量仪观察了压痕试验后试样的三维形貌,探究了"堆积"和"沉陷"现象对试验的影响。观察到的堆积高度均在50微米以下,对试验的影响可以忽略。     

用仪器化的冲击试验系统评定材料的动态性能

由于仪器化的Ｃｈａｒｐｙ冲击试验方法简单经济，已被广泛地用于评价材料的冲击韧性。本文以引进的ＷＯＬＰＥＲＴ冲击试验系统为背景，详细地介绍了计算机辅助的仪器化冲击试验系统（ＣＡＩ）的原理和面貌，对动态断裂韧性Ｋ_（Ｉｄ）的测试原理和方法亦作了较为细致的描述。最后，指出了ＣＡＩ系统几个方面的用途。     

用缺口冲击韧性作为评定铝焊接构件的判据

<正> 一、近况介绍变形铝合金用于受压容器时,其基体材料和焊接接头的屈服强度、抗拉强度、伸长率、弯曲角、硬度和缺口冲击韧性等的最低值均应根据BV30—9/74[1]加以验证。屈服强度、抗拉强度和伸长率之数值系在拉伸试验中确定,并表征材料在单向载荷下的性能。缺口冲击韧性的测定用于评定材料的韧性和脆性断裂的倾向。这个与文献相符的     

TiCN颗粒强化Al2O3陶瓷压痕韧性的统计性质

采用直接压痕法测定了一种ＴｉＣＮ颗粒强化Ａｌ２Ｏ３陶瓷复合材料的断裂韧性，发现在材料表面不同位置测得的压痕韧性值不同，测试结果呈现出较大的离散性。这一离散性可能与材料表面显微结构的不均匀性有关。对１００个测试数据进行的统计分析表明，压痕韧性服从Ｗｅｉｂｕｌｌ分布。     

Vickers压入识别氮化硅断裂韧性

依据仪器化Vickers压入氮化硅断裂韧性实验获得的有关压痕裂纹参数,通过有限元数值分析方法识别出氮化硅的弹性模量和屈服强度,进一步采用虚拟裂纹闭合法确定其裂纹尖端的应力强度因子KI。以此为基础,与氮化硅断裂韧性标准值对比,分析有限元仿真KIC结果和基于L-E-M模型建立的3种典型陶瓷断裂韧性压入测试方法的准确度。结果表明:基于Vickers压入有限元数值分析结果的最大误差仅为2.38%,Anstis公式最大识别误差为2.65%,而Lawn公式和Miyoshi公式的识别误差的绝对值均超过10%,因此Vickers压入测试具有较高测试准确度。     

Evaluation of tensile properties of austenitic stainless steel 316L with linear hardening by modified indentation method

Abstract

The instrumented indentation test has been widely used for the non-destructive evaluation of the tensile properties of metal materials. The true stress–strain curve, yield strength and tensile strength can be obtained by this method. In the present study, a new modified indentation algorithm was used to determine the tensile properties of austenitic stainless steel 316L by taking into account its linear hardening characteristic. As received 316L was solution treated at four different temperatures in the range of 1223–1473K for 2 h followed by water quenching. The effect of solution treatment temperature on the tensile properties of 316L was investigated by the instrumented indentation test using the modified indentation algorithm. Results reveal that the new modified indentation algorithm can be used to estimate the tensile properties of austenitic stainless steel with linear hardening.     

Progress and development in the instrumented Charpy impact test

Toughness is the most important characteristics for structural component materials and has been evaluated widely by Charpy impact test. Charpy test has been presented firstly in 1901, and instrumentation to record load history during impact has been attempted since 1920's. Various methods to estimate quantitative fracture toughness values under dynamic loading condition have been presented. In the development of fracture mechanics, one of the authors has successfully developed the new dynamic fracture toughness testing and evaluation system using the instrumented Charpy impact test, which is called “CAI system”. This paper introduces history of instrumented Charpy impact test and CAI system. Moreover, instrumented impact testing method on brittle materials is also mentioned. Worldwide standard on dynamic fracture toughness evaluation by the instrumented impact testing is highly expected to be established.     

Non-destructive studies on tensile and fracture properties of molybdenum at low temperatures (148 to 423 K)

Tensile and fracture properties of molybdenum have been studied using the automated ball indentation technique. Tests have been carried out at several temperatures in the range of 148 to 423 K at a constant strain rate. Tensile properties determined from these tests agreed well with published results from conventional tensile tests. Temperature dependence of indentation energy to fracture, the fracture toughness parameter specific to this technique using critical stress-to-fracture concept, showed a sharp transition from brittle to ductile condition. These results complement the previous studies on pressure vessel steels, and clearly demonstrate that automated ball indentation technique is a reliable and non-destructive method for determining tensile and fracture properties of materials.     

材料局部性能的球形压痕评价技术研究进展

简介了近几年采用球形压痕法在测试材料性能方面的最新发展和应用.首先概括了球形压痕理论的研究与发展,重点介绍了球形压痕法的应用研究.采用球形压痕法并结合有限元模拟可以获得材料的弹性模量、屈服强度、拉伸强度、应变硬化指数、断裂韧度和应变速率敏感度等性能.通过球形压痕法与通常测试方法比较的结果证实,球形压痕法可以有效评价材料的性能,随着研究和应用工作的不断深入,球形压痕技术有可能在不远的将来成为评价材料局部性能最方便、最简单且相当准确的方法.     

Mechanical properties characterisation of welded joint of austenitic stainless steel using instrumented indentation technique

The instrumented indentation test is a promising nondestructive technique for evaluating mechanical properties of metallic materials. In this study, the localised mechanical properties of welded joint of 304 austenitic stainless steel were characterised with the instrumented indentation test. The single V-groove welded joint was produced using the electric arc welding. A series of instrumented indentation tests were carried out at different regions, including base material, weld zone and heat-affected zone (HAZ). A soft zone regarding strength properties was found in the coarse-grain HAZ. The results show that the HAZ has the lowest yield strength and tensile strength (263.6 MPa, 652.5 MPa) compared with the base material (307.4 MPa, 807.9 MPa) and the weld zone (285.6 MPa, 702.1 MPa). In addition, characterisations of microstructure, microhardness and conventional tensile tests have been performed for comparison. The results reveal that the localised mechanical properties of welded joint of austenitic stainless steel can be represented effectively with the instrumented indentation technique.     

Application of instrumented falling dart impact to the mechanical characterization of thermoplastic foams

The applicability of instrumented falling weight impact techniques in characterizing mechanically thermoplastic foams at relatively high strain rates is presented in this paper. In order to try simulating impact loading of foams against sharp elements, an instrumented dart having a hemispherical headstock was employed in the tests. Failure strength and toughness values were obtained from high-energy impact experiments, and the elastic modulus could be measured from both flexed plate and indentation low-energy impact tests. The results indicate a dependence of the failure strength, toughness, and the elastic modulus on the foam density, the foaming process, and the chemical composition. This influence was found to be similar to that of pure nonfoamed materials and also to that observed from low-rate compression tests. The results also indicate that the indentation low-energy impact tests were more accurate in obtaining right values of the elastic modulus than the flexed plate low-energy impact tests usually used to characterize rigid plastics. The foam indentation observed with this test configuration contributes to obtaining erroneous values of the elastic modulus if only a simple flexural analysis of plates is applied.     

金属断裂表面分形维数与组织、性能之间的关系

借助分形研究了拉伸条件下,分形维数 D_F 与拉伸性能之间的关系,讨论了显微组织对分形维数的影响,并把冲击韧性与分形维数之间的关系和拉伸性能与分形维数之间的关系进行了比较。实验结果表明,拉伸性能与分形维数只存在定性关系。延伸率与分形维数成正比,强度σ_b、σ_s与分形维数成反比,显微组织对分形维数有重要影响。断裂方式对分形维数、断裂性质以及两者的对应关系也有重要影响。     

Dynamic J-R curves and tension-impact properties of AISI 308 stainless steel weld

In this paper, instrumented tension-impact (dynamic tensile) and instrumented Charpy impact test results for AISI 308 stainless steel welds at room temperature are reported. A few Charpy specimens precracked to a/W (crack length to width ratio) ratios of 0.42 to 0.59 were also tested. Dynamic yield strength obtained from tension-impact test agrees well with that from Charpy V-notch specimens. The strain rates obtained during the tension-impact test are compared with the various estimates of strain rates for V-notch and precracked Charpy specimens. A variation of the compliance changing rate method was necessary for determining the crack initiation point while crack growth was determined by power law key-curve procedure. J-R curves thus obtained from Charpy (precracked and V-notch) specimens are compared with those computed using handbook procedures using dynamic tensile results. Key words: Tension-impact testing, 308 stainless steel weld, Charpy V-notch, dynamic fracture toughness, dynamic yield strength, J-R curve, strain rate, key-curve.     

Evaluation of fracture toughness and impact toughness of laser rapid manufactured Inconel-625 structures and their co-relation

The present study involves evaluation of fracture toughness and Charpy impact toughness of Inconel 625 structures fabricated by laser based additive manufacturing. The results of crack tip opening displacement (CTOD) fracture toughness are close to those reported for the Inconel 625 weld metal. The nature of the load–time traces of instrumented Charpy impact tests revealed that the alloy Inconel 625 in laser fabricated condition was associated with fully ductile behavior with Charpy V-Notch impact energy in the range of 48–54 J. Stress relieving heat treatment at 950 °C for 1 h has resulted in marginal improvement in the impact toughness by about 10%, whereas no clear evidence of such improvement is seen in the CTOD fracture toughness. Fractographic examination of the Charpy specimens and the results of the instrumented impact tests imply that the mechanism of crack growth was propagation controlled under dynamic loading conditions. Dynamic fracture parameters were estimated from the instrumented impact test data and compared with the experimentally evaluated fracture toughness results.