Tensile Testing Of Metals Research Articles

Evaluation of the measurement uncertainty during the tensile tests of high-strength bolts

A developed methodology for evaluating measurement uncertainty during the tensile tests of metals and alloys is presented. In this connection, the various sources of uncertainty are considered. The object of studies included high-strength bolts made of 40Kh “Selekt” steel, which were subjected to tensile tests according to the GOST 1497-85 State Standard using a UMM-100 universal tensile testing machine. The basic sources of uncertainty in the measurement of relative elongation and reduction were shown to include repeated measurements of relative elongation; errors of measuring the finite length by a vernier calliper and marking the initial length of a calculated section, as well as the measurement error of the tensile testing machine. These also include operator reading error, repeated relative reduction measurements, as well as the error of measuring the sample diameter by a micrometer before and after the tests. During the measurements, temperature deviation was demonstrated to constitute an additional source of uncertainty when the ambient temperature is different from the standard temperature value ((20±5)°C). Assumptions underlying laws describing the distribution of input values were assigned. Tensile tests are shown to be characterised by two components of uncertainty evaluated as types A and B. A mathematical model constructed for measuring relative elongation and relative reduction during tensile tests is presented. The standard uncertainties of input values are evaluated based on the assumed laws of their distribution. A correlation between the final length of the calculated section, the diameter of the sample following the test, and the applied force, is revealed. Expressions for the calculation of sensitivity coefficients, which characterize variations in the output value (relative elongation) depending on variations of input values, were obtained. The total and extended measurement uncertainties were evaluated. Based on the performed studies, a procedure for evaluating measurement uncertainty when carrying out tensile tests of high-strength bolts was described. The evaluation of measurement uncertainty during the product testing was shown to be a rather labourconsuming work. In this regard, the authors propose the development of procedures for evaluating the measurement uncertainty during the tests with their inclusion into regulatory documents for control methods.

Critical Experiments for Structural Members of Micro Image Strain Sensing Sensor Based on Smartphone and Microscope

Strain is one of the key concerns of structural health monitoring (SHM), and effective measurement of structural strain is very important for structural health condition assessment. The purpose of this paper is to investigate the application of the micro image strain sensing (MISS) sensor based on smartphone and microscope for measuring strain parameters of structural members. Firstly, metal tensile tests were performed to verify the effectiveness of the MISS sensor, and the strain results measured by the fiber Bragg grating (FBG) sensor and the MISS sensor were compared. The results showed that the mean error between the MISS and FBG sensor measured results is 7.1 με in the metal tensile test. Then, a concrete beam bending test was carried out; the mean relative error of strain values between the FBG sensor and the MISS sensor is 2.5%. Overall, the strain measurements of the MISS sensor matched well with those from the FBG sensor in each experiment. This study validates the reliability and accuracy of the MISS sensor for strain detection and the MISS sensors can play a more powerful role in SHM due to their robustness, simplicity, and low cost.

Tensile testing of metals: Relationship between macroscopic engineering data and hardening variables at the semi-local scale

The usual elastoplastic characterization of metals consists of determining the experimental tensile true stress-true strain curve (true curve) and of correcting it for the post-necking triaxiality, in order to obtain an estimation of the equivalent Mises (flow) stress–strain curve. However, especially in the industry, the elongation-based engineering curve is often used because of its simplicity, opposed to the cross section-based true curve, which, instead, is less simple to be measured, unless either measurements of the shrinking specimen area and/or digital image correlation for local strains are used.A new methodology is proposed here for translating the engineering curves into the true curves via material-independent mathematical tools named MVB functions, which only depend on the necking initiation strain and on the aspect ratio of the undeformed cross specimen. The true curves delivered by the MVB functions can be then translated into the flow curves via the MLR correction, proposed by the authors in 2004. The MVB functions are found to work properly for various specimens with round, square and thick/thin rectangular cross sections, provided that the specimens slenderness (ratio of length to section area) is large enough to prevent the necking-induced stress triaxiality to overlap with the triaxiality induced by the specimen shoulders.Nine arbitrary hardening laws are adopted for checking the validity of the MVB functions by finite elements, encompassing very different combinations of early/medium/late necking strains and low/medium/high hardening slopes. The flow curves of the above arbitrary materials are obtained as Ludwik functions, which, beyond the necking onset, become linear true curves corrected via the MLR function. It is worth noting that such hypothesis about the flow curves, widely supported by literature data, also imposes a remarkable constraint to the way the curvature of the flow curve and, then, the hardening itself, may evolve in the post-necking range.The material independency of the relationships between engineering curves and true curves nicely complies with the evidence that the necking evolution is a purely geometric phenomenon, as it was also found in previous works.The experimental validation is provided by in-house tests and by literature data referred to round and thin sheet specimens.

Crack driving force prediction in heterogeneous welds using Vickers hardness maps and hardness transfer functions

Flawed welds often require an Engineering Critical Assessment (ECA) to judge on the necessity for weld repair. ECA is a fracture mechanics based prediction of the integrity of structural components with defects under operating conditions. Adding to the complexity of a weld ECA is the occurrence of local constitutive property variations in the weldment (‘weld heterogeneity’). Their quantification allows for a more accurate assessment compared to common (standardized) practice, which assumes welds to be homogeneous. Hardness measurements allow to quantify weld strength heterogeneity given their theoretical relation with ultimate tensile strength. However, various standards and procedures report a wide variety of relations (‘transfer functions’) between hardness and strength, and recognize substantial scatter in hardness based predictions of strength. Within this context, this paper investigates the suitability of Vickers hardness mapping to perform an accurate weld ECA for high strength low alloy steel. To overcome the scatter associated with standardized transfer functions, this paper suggests an experimental calibration procedure based on all weld metal tensile tests. Finite Element (FE) analysis has been conducted on welds originating from steels to simulate their crack driving force response in Single-Edge notched Tension (SE(T)) specimens. Vickers hardness maps and hardness transfer functions are combined to assign element-specific constitutive properties to the model. The transfer function calibrated by all weld metal tensile tests yields a better agreement with experimental load-CTOD curves than transfer functions mentioned in standards and codes. Finally, a step-by-step procedure facilitates a practical adoption of the methodology.

Experimental Study on the Low-Cost Iron Wire Fiber Reinforced Asphalt Concrete

The usability of low-cost iron wire fiber for the reinforcement of hot asphalt mixtures was investigated with experimental tests in this study. Five mixtures having different fiber content of 1%, 3%, 5%, 7%, 9% and control mixtures were prepared. Characteristic properties of bitumen, aggregate and iron wire used in the mixtures were determined by thermogravimetric analysis (TGA), conventional bitumen tests, conventional aggregate tests and metal tensile tests. After optimum bitumen rate was determined, Marshall Stability Test, Cantabro Tests were performed in order to measure perfomance of the mixtures. Additionaly, moisture susceptibility of samples was determined with indirect tensile test. As a result of indirect tensile tests, indirect tensile strength (St) and indirect tensile strength ratio (ITSR) values were calculated. The results of the investigations indicate that the addition low-cost iron fiber in the amount of 1%-3% improved performance of asphalt mixtures. When the used fiber rate was increased more than 3%, clustering created by fibers was observed by using stereo-microscobe. Consequently, air voids were increased and bitumen-aggregate interaction was decreased. Increasing fiber ratio especially, at 7-9 percent caused compressing, durability and stability problems in the mixture.

On the Accuracy in Determination of the Mechanical Material Characteristics at Low Temperatures

The paper considers the processes related to the specimens and loading device in the tensile testing of metals in strain-controlled mode, including under the conditions of cryogenic temperatures up to 4.2 K. It is demonstrated how the potential elastic energy accumulation and its subsequent relaxation in the development of the specimen strain affect the process of kinetics. The strain rate dependencies on the strain value and stiffness factor (relation between the values of stiffness of the specimen and the machine) are obtained. Noteworthy is that the values of initial and nominal strain rates can differ by an order of magnitude in case of the machine compliance. To obtain the strain rates that are similar for different machines at the initial stage of the process, the formula is proposed allowing one to calculate the required nominal rate. At the temperatures lower than 30 K there is a dramatic increase of the influence of the machine stiffness, dimensions and shape of the specimens on the obtained characteristics, which requires the special measures in the process of testing. Some international and national standards are considered. It is shown that, at present, the process of standardization for tensile testing of metals is inadequate, and the requirements of the current regulatory documents are the minimum, which are not in agreement with the development paces of testing equipment. To significantly enhance the level of accuracy of the obtained mechanical characteristics, it is required to employ the urgent measures as the machine compliance limitation, as well as the decrease of the dimensions range for the specimens together with the standardization of the permissible range of the stiffness factor, and the required selection of the nominal strain rate considering the latter.

Materials Science: Academic Laboratory Experiments

This document presents an overview of academic laboratory experiments in the field of materials science. It summarized the physical principles, setting up, results and conclusions of lab experiments that were conducting at the German-Jordanian University in the summer semester 2009. The experiments cover the following topics: tensile testing of metals, hardness testing, the behavior of metals under high strain rate loading (impact test), bending test, the preparation of metallic specimens for micro‐examination, scanning electron microscope, corrosion principles, hardening steel using different quenching media, hardenability and Jominy test, tensile testing of plastics, and melt mass flow rate of thermoplastics.

Numerical analysis of the deformation instability of metals in liquid helium

Numerical results on the discontinuous yielding of austenitic steel and aluminum alloy at a temperature of 4K are presented. The method used allows qualitative and quantitative predictions of the influence of eight determining factors, including characteristics of the material and parameters of the loading system, on the low-temperature discontinuous deformation of metals. Recommendations are formulated on how to improve standards on tensile testing of metals in liquid helium as regards machine rigidity, standard specimen sizes, and new mechanical characteristics.

On standards for mechanical testing of materials at cryogenic temperatures

The basic principles of the ASTM, ISO, and GOST standards specifying the procedure for tensile testing of metals at liquid helium temperatures are considered and analyzed. The main factors that influence the parameters of the strain- and stress-controlled loading, as well as the dimensions of specimens in tests of metals and alloys under the above temperatures are determined. Recommendations on extending and revising the provisions of standards are provided.

Peculiarities of neck formation under low-temperature discontinuous yield of metals. Part 2. Plane strain

The regularities of repeated necking have been studies on flat specimens of alloys for cryogenic engineering in the case of effect of low-temperature discontinuous yield. It has been shown that in contrast to cylindrical specimens, in this particular case there is a considerable deviation of the stressed state from linear stress, which affects greatly the mechanical characteristics determined and does not allow flat specimens to be recommended for standard mechanical tensile tests of metals at temperatures below 30 K.

Mechanical Properties of Weld Metal for Fire-Resistant Steel with Large Heat Input Submerged Arc Welding.

Large heat-input welding is increasingly employed because of its high productivity. For this welding, titanium and boron (Ti-B) bearing welding materials are suitable in acquiring high toughness at low temperatures. However, their properties at high temperatures have not been known. Preferable ductility at high temperatures is required when they are applied to the welding of fire-resistant steels. The present study examines the mechanical properties of Ti-B bearing welding materials for fire-resistant steels in large heat-input welding.Submerged arc welding with two electrodes in tandem was conducted with the heat-input of 13 kJ/mm. The mechanical and metallurgical investigation were v-notch Charpy tests, weld metal tensile tests, chemical analyses, and metallographic observation on ruptured surfaces.It was found that the addition of titanium and/or boron lowers the high temperature elongation. This reduction was caused by grain boundary fracture at the prior-austenite grain boundaries of the weld metal with titanium and boron. However, the high temperature properties were recovered in the weld metal with titanium as low as 30 ppm and nil boron, and this weld metal fractured in an intragranular mode with enough toughness.

Methodology for destructive tensile testing of metals at very low temperatures

Methodology for destructive tensile testing of metals at very low temperatures

747. Tensile tests of metals under high vacuum conditions: Anon., New Scientist, 18 (335), 18 April 1963, 154

747. Tensile tests of metals under high vacuum conditions: Anon., New Scientist, 18 (335), 18 April 1963, 154

Tensile tests of metals under high vacuum conditions

Tensile tests of metals under high vacuum conditions

The Influence of Time on the Elongation of Soft Rubber under Constant Load

Abstract According to specifications for the testing of rubber prepared by Committee Thirteen of the Deutscher Verband für die Materialprüfung der Technik, there are at the present day two common and at the same time distinct methods for studying the mechanical properties of soft rubber, viz., tensile tests, and, secondly, determinations of elasticity. As carried out in practice, the tensile test is based fundamentally on the tensile testing of metals. With its great elastic properties, however, soft rubber exhibits to a very high degree changes in its elongation with time, and earlier testing methods give relatively unsatisfactory information about the effect of time during the stretching of rubber. Of course the determination of elasticity in the specifications mentioned above, where the so-called permanent elongation is measured, gives a certain insight into this influence of time. Nevertheless this earlier method is not suitable for obtaining comparable results in all cases.

THE EFFECT OF TEMPERATURE ON TENSILE TESTS OF METALS

Journal of the American Society for Naval EngineersVolume 24, Issue 4 p. 1396-1407 THE EFFECT OF TEMPERATURE ON TENSILE TESTS OF METALS First published: November 1912 https://doi.org/10.1111/j.1559-3584.1912.tb04684.xAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Volume24, Issue4November 1912Pages 1396-1407 RelatedInformation