钢绞线拉伸试验的夹具及引伸计的改造应用

钢绞线强度高,缺口敏感性大,拉伸试样长,对它进行拉伸试验,必须具备特制的夹具和大标距引伸计,本文介绍了改造后夹具与引伸计在钢绞线上试验中应用的成功经验.     

视频引伸计标定装置设计及标定方法研究

视频引伸计被用于测量材料的变形,需要进行在线标定和校准,然而目前尚无相应的标准和校准规范的指导,针对此,设计了一种光栅式引伸计在线标定装置,主要由控制器、步进电机、机械传动机构、光栅位移传感器、显示器以及上标定板、下标定板组成。第三方校准结果显示,该装置标距标定板最大相对示值误差为0.07%(Urel=0.04%,k=2);光栅位移部分技术指标:小于等于1/3mm时,绝对误差小于0.3μm(U=0.1μm,k=2),大于1/3mm时,相对误差小于0.1%(Urel=0.04%,k=2),技术指标明显优于使用要求。用该装置对视频引伸计进行了重复性和稳定性验证实验,对标定结果评定了不确定度。结果表明:该装置技术指标完全满足视频引伸计的在线标定。     

变标距电子平均值引伸计

着重介绍了一项专利技术——钢筋电子平均值引伸计,它的主要特点是标距可以在较大范围内作连续变化,能满足带肋钢筋机械连接试验的要求;另外还讨论了电子平均值引伸计的电桥的并联接法和串联接法的特点,以期对引伸计的研究、生产和选用提供参考。     

视频引伸计用纤维复丝拉伸测试技术的研究

介绍了视频引伸计在复丝拉伸测试中的应用,对视频引伸计进行标定,编辑复丝拉伸测试程序。可准确测试复丝的拉伸强度、拉伸弹性模量、断裂伸长率,是最先进的复丝性能测试技术。     

引伸计的过去和现在

通过对过去机械式引伸计(包括杠杆式引伸计、镜式引伸计、蝶式引伸计和球铰式引伸计)的介绍,说明了在材料拉伸试验过程中,为了扣除偏心拉伸的弯曲变形对试验结果的影响,一般都需要在拉伸试样的两侧各安装一只引伸计进行同时测量.对现在经常使用的电子引伸计(包括单侧电子引伸计、平均值引伸计、双侧电子引伸计、视频引伸计和自动引伸计)也...     

双频激光干涉仪在引伸计标定器示值误差校准中的运用

介绍了采用双频激光干涉仪作为标准器,对引伸计标定器的示值误差进行校准的方法,并阐述了校准工作中的数据处理过程。与传统的校准方法相比,本文的工作最大限度地消除了校准过程中的各类测量误差并提高了工作效率。     

双侧电子引伸计的原理和误差分析

首先对单侧电子引伸计测量结果不稳定及误差较大的原因进行了分析,然后对双侧电子引伸计的测量原理进行了介绍,建立了斜线伸长量与拉伸试样轴向伸长量之间的关系,证明了双侧电子引伸计的测量结果不受偏心拉伸的影响,其系统误差很小甚至可以为零。     

GSYB型光栅数显式引伸计标定仪的研制

为了解决在0.5级引伸计示值误差和进回程示值误差测量工作中存在:B类引伸计标定器的测量准确度有不满足;A类引伸计标定器的给定位移量受量块标称尺寸所限制而有测量点不能均匀分布以及测量工作效率低等问题.研制出GSYB型光栅数显式引伸计标定仪,其性能指标完全满足0.5级引伸计示值误差和进回程示值误差的测量准确度要求.同时,还可实现检测原始记录和数据处理的智能化,大大提高了检测工作效率.     

断后标距的重量法测定

为了失效分析，无标点等特殊情况下断后标距的测量，提出了用重量法测量断后标距。试验结果表明，该方法可作为仲裁方法。     

试验参数对不锈钢包壳管环向拉伸的影响

包壳管是反应堆内重要的安全屏障,其在服役环境下承受一定裂变气体内压,同时面临芯块和包壳间机械相互作用的考验.开展包壳管环向拉伸性能研究,对反应堆燃料组件设计和安全分析具有重要意义.奥氏体不锈钢是快中子反应堆包壳管重要候选材料,具有良好的高温力学性能.本文针对奥氏体不锈钢包壳管高温环向拉伸试验,研究了夹具、标距段宽度和润滑条件等试验参数对包壳管环向拉伸试验的影响.结果表明:三嵌块夹具可以避免试样标距段向内展平,且夹具和试样间摩擦力较小;标距段的宽度对包壳管环向拉伸强度影响不大,但是标距段宽度过大或者过小都会造成试样延伸率下降;夹具与试样间隙的摩擦会增加拉伸载荷,降低延伸率,使用石墨润滑可以有效减小摩擦力的影响.     

Anisotropy of tensile behaviour in a duplex stainless steel sheet

Abstract

Unusually large anisotropy of strength has been observed in commercially produced sheets of a duplex stainless steel, Fe–1·5Mn–22Cr–5·5Ni–3Mo–0·15N. The austenite and ferrite phases in this material are highly elongated and possess unusually sharp preferred crystallographic orientations. Both phases are in a recrystallized condition and have almost equal hardnesses. On the basis of the present measurements and a crystallographic analysis of plastic flow it is concluded that the observed anisotropy cannot be due to composite reinforcement in the duplex structure but is rather a result of texture hardening.

MST/214     

Inclined tensile strength of steel fibres in a cement-based composite

An investigation of the behaviour of steel reinforcing fibres in a cement-based composite inclined to the direction of tensile load was carried out. Steel fibres with widely differing fibre parameters were tested and a new fibre characteristic, the inclined tensile strength (its), was identified. It was observed that the value of the its decreased with increasing inclination angle but the decrease varied according to the type of fibre. The ultimate tensile force sustained by the inclined fibres depended also on the magnitude of the strain. It indicated that for some types of fibre the properties of a randomly reinforced fibre composite after the first crack depended much more on the inclined fibres and their its than on the fibres aligned to the principal stress.     

Correlation of tensile test properties with those predicted by the shear punch test

In the development of experimental alloys having sufficient material to do a standard tensile test procedure is not always possible. Thus in this work, we have evaluated the ability of the shear punch test to predict the strength and ductility of materials in place of the tensile test.This correlation study was carried out experimentally using six different alloys, and validated using finite element modelling. Both the experimental and modelling data confirmed that the yield point and ultimate tensile stress can be accurately elucidated from the shear punch data.However, the punch displacement at failure was found to be a function of both the ductility of the material and its work hardening rate. Although corrections were developed using the FE simulations which satisfactorily predicted tensile ductility from to the simulated shear punch displacement, back extrapolation of the tensile ductility from experimentally measured shear punch tests were not possible.It was concluded that the shear punch test suitable for determining the strength of a material, but not able to be used to infer the equivalent tensile ductility due to both experimental error in determining the point of failure as well as the interdependence of the punch displacement on multiple material properties.     

Void nucleation during tensile deformation of a C-Mn structural steel

Various methods have been used to reveal the voids arising from ductile fracture processes in a structural steel and the techniques compared. Using a series of the interrupted smooth bar tensile tests specimens were stopped at different plastic strains and nucleation was investigated. The material tested was a C-Mn structural steel with low sulphur content. The critical nucleation strain and the relative void volume at the critical nucleation strain were determined.Résumé On a fait appel à diverse sméthodes pour faire apparaitre les lacunes générées par un processus de rupture ductile dans un acier de construction, et les techniques utilisées ont été comparées.En procédant à une série d'essais de traction interrompus sur un barreau lisse, on a pu isoler différents spécimens de déformation plastique et étudier les nucléations de lacunes y associées. Le matériau soumis à l'essai était un acier de construction au C-Mn à faible teneur and S. On a pu déterminer une dilatation critique de nucléation, ainsi que le volume relatif de lacunes créées à la dilatation critique de nucléation.     

In-situ observation of microcrack evolution in a dual-phase steel during tensile straining

ABSTRACT

In this paper, the microcrack evolution in DP590 dual-phase steel was observed by in-situ straining in straining transmission electron microscopy. It was found that a void initiated ahead of a main crack. After the load was applied, a thinned area was nucleated ahead of the void tip, and it grew gradually into shallow nanovoid, penetrating nanovoid, and then new void. Meanwhile, the old void connected with the main crack. The repetitions of the procedures resulted in the continuous propagation of a crack. Interaction between microcracks was observed. The propagation direction of one microcrack may change, affected by other microcracks. Voids were observed between microcracks and have a significant effect on the coalescence of microcracks.     

Application of a digital computer in the processing and presentation of tensile test results

A computer program has been prepared to receive the longitudinal and lateral strain readings taken during tensile tests on cast irons and to compute from them the longitudinal and lateral moduli of elasticity and Poisson's ratio. The results are presented as mathematical functions of stress.     

Conventional and in situ tensile test of friction stir welded steel – Optimization of processing parameters

In the present investigation, steel plates were joined at different tool traversing speed by friction stir welding keeping other parameters same. Microstructural characterization was carried out with optical and scanning electron microscopes. At weld nugget pearlite and bainite were present within ferrite matrix. Thermo‐mechanically and heat affected zones microstructure consisted of pearlite and ferrite. Second phase area fraction and matrix grain size at different regions were varied depending on welding parameters. Weld nugget exhibited substantial improvement in microhardness with respect to base metal. In this respect heat affected zone revealed minimum microhardness and was below base metal value. Tensile tests were carried out on standard and miniature specimens in scanning electron microscope. Highest joint efficiency to the tune of ～82 % and ～120 % of that of base metal obtained for standard and miniature specimens, respectively machined from weld fabricated at lowest welding speed. With increment in welding speed assembly strength was reduced for both types of specimens. Standard specimens failed from heat affected zone and miniature specimens failed through centre of weld nugget. Apart from matrix grain size and second phase area fraction, precipitation of microalloyed carbide / carbonitride was responsible for altering the joint strength.