Plate Tensile Test Research Articles

Phase-field fracture modelling of piezoelectric quasicrystals

In this paper, an electro-elastic phase field model is developed for brittle fracture in piezoelectric quasicrystals. The elastic field of quasicrystals is composite of a phonon field and a phason field. The phonon field, phason field and electric field are coupled with each other, and the phonon and electric loadings trigger the variation of both the phonon and phason elastic energies, which then together contribute to crack evolution. The cracks initiation and propagation in piezoelectric quasicrystals under quasi-static mechanical loading and electric loading can be well predicted. Several numerical examples are performed to evaluate the effects of electric field and anisotropic fracture toughness. Simulation results show that the electric field influences the initial force, peak force, fracture displacement and crack path. For the single-edge notched tensile test, the effects of electric field force on the initial force, peak force and fracture displacement are obvious. For the single-edge notched shear test, the electric field force has no effect on the initial force, but it affects the peak force, fracture displacement and crack path. For the porous plate tensile test, a high-intensity electric field can deflect crack substantially resulting in passing through different holes. Further simulation indicates that the anisotropic fracture toughness has a significant effect on peak force, fracture displacement, and crack path. The present model can be used to simulate various fracture problems of piezoelectric quasicrystals.

Research on the micro zone strength and strain hardening behavior in the 30Cr2Ni4MoV rotor welded joint

In order to investigate the micro zone tensile properties of a 30Cr2Ni4MoV rotor welded joint used for an ultra-supercritical steam turbine, a thin plate tensile test method is put forward by taking the micro zone size into account. The microstructures of welded joint are observed by OM, SEM and TEM, and a strength prediction model based on the microhardness and the strain hardening exponent is established. The researches show that the weld metal (WM) has lower strength than the base metal (BM), but similar plasticity and strain hardening ability, that the heat affected zone (HAZ) has a sharp distribution of tensile strength due to the great changes in grain size and microstructure. Based on the hardening rate analysis with Kocks-Mecking (K-M) model, the coarse-grained HAZ (CGHAZ) only experienced two strain hardening stages Ⅲ and Ⅳ, and other micro zones of the welded joint exhibited three strain hardening stages Ⅲ, IV and Ⅴ. The coarse tempered martensite in CGHAZ has poor coordination deformation ability, resulting in its short strain hardening stage IV. More tempered bainite and finer tempered martensite are beneficial to extending the strain hardening period. By observing the microstructures after tensile tests, it is found that the dislocation cells formed more uniformly in the tempered bainite than in the tempered martensite, and only the intragranular carbides have a beneficial effect on the strain hardening behavior. An equation for predicting the micro zone strength is established, and the micro zone strength distribution along the welded joint is successfully predicted.

Crack initiation and propagation of defects adjacent to the X65 pipeline spiral weld under axial tensile force

The pipeline structure is prone to fracture by the synergistic effect of external forces and defects, which may lead to disastrous consequences. Therefore, it is of great engineering significance to study the crack initiation and propagation of defected pipelines. In this study, a series of simulations and experiments based on the wide plate tensile test were carried out. The effects of the size and position parameters of the defects adjacent to the pipeline spiral weld on crack initiation and propagation were investigated. The simulation results show that the dimensions of a single defect affected the crack initiation and propagation. Besides, the experiment results show that the mutual influence on the crack initiation and propagation between two defects was related to the position and distance of the double-defect. Observations of the pipeline stress and strain revealed that compared with the centrosymmetric double-defect, the likelihood of the fracture of the pipeline with the axisymmetric double-defect increased when the distance between the two defects was the same.

Anisotropic mechanical behavior prediction of aluminum alloy sheet based on an anisotropic GTN model: Modeling, simulation and experimental investigation

The rolled aluminum alloy sheets usually have anisotropic properties that affect its ductile fracture behavior. In order to study the plastic anisotropy and ductile fracture behavior of aluminum alloy 6016 sheet, the Hill48 anisotropic yield criterion is introduced into the Gurson–Tvergaard–Needleman (GTN) model forming an anisotropic GTN model. In this model, two groups of Hill48 anisotropic yield constants, which are respectively calculated by Lankford's coefficient in different directions and the combination of the Lankford's coefficient and yield stress in different directions, are separately used to describe anisotropic mechanical behaviors. The failure void volume fraction is identified through microstructure analysis and the other damage parameters are calibrated through a finite element (FE) inverse calibration method. The abilities of these two groups of Hill48 anisotropic yield constants in predicting anisotropic mechanical behaviors of aluminum alloy 6016 sheet are examined by performing FE simulations of 0°, 45°, and 90° plate tensile tests, deep-drawing tests and Erichsen cupping tests. Results show that the Hill48 anisotropic yield constants calculated by the Lankford's coefficient in different directions have a better ability to predict local anisotropic plastic deformation especially the earing effect in the deep-drawing test, but the Hill48 anisotropic yield constants calculated by the combination of the Lankford's coefficient and yield stress in different directions have a better prediction ability in predicting global anisotropic mechanical behaviors of the aluminum alloy 6016 sheet.

Full-scale experimental investigation of the fracture behaviours of welding joints of APL X80 wide plate based on DIC technology

With the advances in material research and pipe manufacturing, the construction of oil and gas pipelines is developing continuously, and the evaluation of welding joints with defects has become the focus of pipeline safety research. In this study, two full-scale wide plate tensile tests were performed on Ø1422 mm × 25.7 mm X80 specimens with original and repaired welding joints. By comparing and analysing the experimental load–displacement responses, as well as the synchronous monitoring results of strain gauge and digital image correlation (DIC) system, the variation trend of the crack mouth opening displacement (CMOD) with distal strain, and the strain capacity of welding joints under different critical CMOD conditions were obtained. This way, the difference in bearing capacity between the original and the repaired welding joints was further determined. Under the same load condition, the driving force of the defect crack expansion at the repaired welding joint was smaller. When the critical CMOD was 0.5 mm and 1.0 mm, the strain capacity of the repaired welding joint was increased by 0.12% and 0.35%, respectively. Therefore, the repair operations of the welding joint effectively strengthen its deformation capacity. This research can provide a valuable data basis for the subsequent verification of numerical analysis models, and can also be referenced for the safety evaluation of pipelines with crack defects.

Research on the establishment and influence mechanism of critical wrinkling limit diagram (WLD) of plate and shell forming under mold constraints

With the rapid development of manufacturing technology in the fields such as aerospace, aviation, national defense, and automobiles, the demands for lightweight, toughening, and forming accuracy of products have increased. As one of the main defects in the plastic forming of thin-walled components, wrinkling failure has always been a key element in forming control. The sheet metal is restrained by the mold in actual forming process and the wrinkling is significantly affected by the boundary conditions. To study the effect of the mold constraints on the wrinkling failure in the actual forming process, a stretching wrinkling test of wedge plate with the boundary constraint conditions of mold was designed. By establishing the simulation model for wrinkling failure of sheet forming under mold constraints and its wrinkling limit diagram (WLD), the accurate prediction of sheet metal wrinkling failure form and the critical state in actual forming was realized. At the beginning of the research, the wedge plate tensile test was implemented for using as verification for simulation results, then the wrinkle simulation model of Buckle-Dynamic with the instability mode as the initial defect was established. By combining with the non-contact full-field strain measurement system DIC to obtain the strain data of the specimens in the test process, the accuracy of the simulation model was verified. On this basis, the critical wrinkling limit diagram (WLD) was established for the wrinkle partition on the wedge specimen, and the influence of stress state, stress loading path, principal compressive stress increment, principal stress ratio factors on the distribution and propagation direction of wrinkles, as well as the morphology and characteristics of WLD are discussed. The research content of this study is of guiding significance for the prediction of the actual wrinkling failure of sheet and shell forming.

Design and Research of 2000T Wide Plate Tensile Testing Machine

Wide plate, wide plate weld, pipeline girth weld and plate welded of panel used to the storage tank were wholly stretched by 2000T wide plate tensile test machine when using the related fixture. Tensile strength, initiation crack position of the joint crack, tolerance of the existing defects of welded joint, possibility of the crack propagation and fracture were studied. Their weak links were found, the formation of defects were avoided by welding technology and technical means. The closed loop control was realized by using advanced servo valve and high performance measure and control system, computer technology was used fully, multifunctional test control of the machine was realized. A number of servo cylinder precise synchronous control loading mechanism was adopted by 2000 T wide plate tensile testing machine, the design of its loading mode, servo cylinder, sensor installation layout and combined structure of super power sensor was the first in China, which created a platform for the development of large structure testing machine in the future.

An improved shear modified GTN model for ductile fracture of aluminium alloys under different stress states and its parameters identification

To solve the problem that the original GTN model cannot accurately simulate ductile fracture of material under low stress triaxiality, many scholars have made shear improvement to it, but these shear modified GTN models have their own advantages and disadvantages and the parameters are difficult to be determined. An improved shear modified GTN (ISMGTN) model containing two independent damage mechanisms is proposed for ductile fracture prediction of materials under different stress states. The shear damage parameters, tensile damage parameters and the hardening parameters are identified using a FE inverse identification method incorporating the Latin hypercube design, Kriging approximate model and NLPQL optimization method performed in the optimization software ISIGHT. Influence of each damage parameter on damage evolution under different stress states is analyzed by a unit cell model. Accuracy of the ISMGTN model and feasibility of the damage parameters identification method are verified by performing them on a material aluminum alloy 6061 with 0°, 30° and 60° shear tests, plate tensile tests, and notched tensile tests. Additionally, fracture morphology analyses of the fractured specimen and contour plots of the effective tensile damage and effective shear damage from the FE analysis using the identified parameters are performed to study possible mechanism of deformation and failure in microscale and macroscale perspectives, respectively, and a good consistence is obtained.

Development of simplified evaluation method of brittle crack arrest toughness on small-scale bending test in steels

The priority items in the safety evaluation of steel structural components generally include an ability to arrest crack propagation, which is necessary to prevent a catastrophic failure even if a brittle fracture occurs. The ‘double integrity’ concept of brittle crack initiation control and arrest has been considered to be an effective and rational methodology for several decades. The wide plate tensile test such as ESSO test is one of the major methods for evaluating brittle crack arrest toughness of steel plates. Although ESSO test makes it possible to accurately evaluate arrest toughness which indicates the Arrhenius type temperature dependence, it is not suitable for quality assurance test at mass production of steel plates due to its high economical cost and long lead-time. Thus, a number of studies has attempted to establish simplified evaluation method of brittle crack arrest toughness for many years. Generally, bending test is certainly one of the most hopeful methods since it does not require a relatively high test load. However, the phenomenon that brittle crack propagates at extremely high speed in bending condition becomes highly complicated. When brittle crack propagates at almost the same speed as stress wave in bending condition, stress distribution is the middle of the initial state and fully reallocated state by the static equilibrium. It is not easy to make out the detail only by theoretical consideration. In this study, by performing the dynamic elasto-plastic FEA in various test designs based on SEN(B) test, the authors calculated the stress distribution at the crack tip and developed a new test design suitable for evaluating arrest toughness. Moreover, the authors investigated the correlation between the result of ESSO tests and that of the developed tests and presented its applicability.

Toughness assessments of laser arc-hybrid welds of ultra high strength steel

This paper investigates the toughness properties of laser arc hybrid welds of HT980 (980 N/mm2 class) and HT780 (780 N/mm2 class) steels. In the Charpy tests, a side groove specimen, along with the standard V-notch specimen, is employed to try prevention of fracture path deviation. A three-point bending test, a double-edge notch tensile (DENT) test, and a deep notch (DN) test are performed to measure the critical crack tip opening displacement (CTOD) at brittle fracture initiation. It is demonstrated that the critical CTOD is affected by the loading mode; critical CTOD by tension test is apparently higher than that by bending test. Nevertheless, three-point bend critical CTOD has exceeded the CTOD required value evaluated by WES2805 (“Method of Assessment for Flaws in Fusion Welded Joints with Respect to Brittle Fracture and Fatigue Crack Growth”) design curve with the allowable stress designed for an assumed crack. It has been observed that even though fracture pass deviation (FPD) occurred in a Charpy impact test, a straight brittle crack propagated throughout welded metal in a notched wide plate tensile test that was conducted at the same testing temperature as that of the Charpy impact test.

A study on the material characteristics and the welding properties of the HSA800 steel

In this research, 7 species of material characteristics test and 9 species of welding properties test for FCAW and SAW were proceeded to confirm the various material characteristics and welding properties of HSA800 developed recently. As a result of material test, HSA800 steel satisfied the KS and the criteria of homogeneity for the strength of the steel, confirmed as sound steel having excellent directivity and toughness. Test results of the FCAW and SAW partially satisfied the KS and the criteria of homogeneity for the strength of the steel, and confirmed as having a good weld zones. However, the result of SAW weld zone chemical composition test showed that the P composition is not satisfying the KS. According to the result of weld zone rod and plate tensile test results, the FCAW 1G appeared more better than the FCAW 3G, and the SAW PH2 appeared more better than the SAW PH1.

Mechanical properties of GFRP slip-form for in-situ application

In this paper, a more effective construction method is introduced, wherein the mechanical advantages of Glass Fiber Reinforced Polymer (GFRP) are applied to the slip-form method. The slip-form method, which is a typical moving form method, has advantages such as reduced construction duration and simple components because it enables continuous forming work of concrete in a single construction. However, it is vulnerable to corrosion, quality control is difficult, and the form plate cannot be reused. In this study, a tensile test was carried out on a GFRP plate by using a new method to apply the steel form to the GFRP plate. Effective GFRP slip-form shape and the application method were proposed by conducting finite element analysis and parametric analysis based on the results of the GFRP plate tensile test; performance was verified through a structural test. From the test results, the GFRP slip-form showed better structural performance than the steel form, and the GFRP slip-form construction method may reduce costs because of its reusability, easy quality control, and reduced construction duration.

Constraint analysis of defects in strength mismatched girth welds of (pressurized) pipe and Curved Wide Plate tensile test specimens

Curved Wide Plate (CWP) specimens are often considered to evaluate the tensile strain capacity of girth weld defected pipelines. However, to date no comparison has been made between the constraint in CWP and (pressurized) pipe specimens. This paper reports on the evaluation of the constraint through three dimensional finite element simulations. At first, it is observed that the internal pressure marginally increases the out-of-plane constraint. Second, the CWP specimens appear to closely represent the constraint in pipe specimens for homogeneous as well as strength mismatched situations. CWP specimens become increasingly conservative to pipe specimens with increasing defect dimensions.

A Refined Model of Three-roller Elastoplastic Asymmetrical Pre-bending of Plate

The geometry of plate after edge pre-bending mode is compared with that after roll-bending mode and the relationship among edge pre-bending angle, pre-bending edge length, and cylindrical desired radius is presented for a three-roller plate bender with bottom rollers adjustable horizontally. The analytical moment-curvature model and springback model for pure bending arc established, assuming that the stress-strain relationship of material is linear, and the material is in plain strain and yields according to Mises yield criterion. The mathematical model for three-roller edge pre-bending of plate is developed considering the effect of pre-bending edge length, bottom roller radius, friction between plate and roller, etc. The plate tensile test and plate bending test arc done and the numerical results agree well with the test data. The results arc shown graphically and analyzed in the following aspects: (1) the error between numerical results and test data of top roller force; (2) the influence of bottom roller radius, relative curvature, and bending arc length on springback angle; (3) the relationship between springback ratio and edge pre-bending angle.

Study on ductile crack initiation limit from notch root of pipeline girth welded joints with strength mismatch

This study investigated ductile crack initiation limit of pipeline girth welded joints with different strength mismatches. The ductile crack initiation limit for the girth welded joints was evaluated by conducting three-point bending fracture toughness tests and wide plate tensile tests with a surface notch. In addition, effect of heat input on the ductile crack initiation limit of weld metal (WM) was evaluated on the assumption that a welding condition would be varied in the field in the actual pipeline construction. As the results, the equivalent plastic strain at the notch tip for the ductile crack initiation of the three-point bending tests was consistent with those of the wide plate tests, and the heat input hardly affected the ductile crack initiation limit within the range of this study. This meant that the ductile crack initiation limit of the pipeline girth welded joints with strength mis-match was able to be estimated using the equivalent plastic strain obtained from the three-point bending tests. Based on these results, we proposed a procedure to determine the rational fracture toughness requirements which took into account the difference in the plastic constraint between standard fracture toughness test and pipeline girth welded joints. This procedure was also possible to determine the required strength matching level for a strain-based design for girth welded joint containing surface notch in the centre of the WM in terms of preventing the ductile crack initiation.

Fractography of burst-tested linepipe

The fracture mechanism of fast running ductile crack was investigated from the viewpoint of microscopic fracture appearance. Fracture surfaces were sampled from burst linepipes after full-scale burst tests, and examined by scanning electron microscope (SEM). In spite of sufficient thickness reduction due to local necking, the macroscopic appearance of the burst-tested specimens was a slanted fracture in the wall thickness direction. The microscopic observations revealed an equiaxed dimple pattern on the fracture path in the thickness direction tilted to the maximum shear stress direction. The Charpy impact test, drop weight tear test (DWTT), plate tensile test and round bar tensile test were also performed with the same materials as in the full-scale burst tests. The size and frequency of the primary dimples on the fracture surface of the laboratory specimens were compared with those of the full-scale burst linepipe. The stress state at the running crack tip in the full-scale burst test was also investigated based on the dimple morphology.

Determination of ductile damage parameters by notched plate tensile test using image analysis

A determination method was proposed for deciding material properties relating to ductile fracture limit (damage parameters) through a tensile test. Gradual changes in a necking shape of the tensile test specimens were measured by a notched plate tensile test using image analysis. Using the tensile test, strain and stress changes at the necking along various deformation paths were obtained. Critical damage values of integrated ductile fracture equations were estimated, and they changed depending on initial notch radius and aspect ratio of plate tensile testpiece. Furthermore, stress triaxiality and equivalent strain change were measured to investigate the influence of aspect ratio of width and thickness of testpiece on equivalent strain at final failure. It was found that ductility of steel decreases with the decrease in the aspect ratio.

Fracture Toughness of Thick Steel Plates for Shipbuilding

In this study, the effect of thickness on the fracture toughness of the steel plate with the thickness of 80mm has been investigated by the wide plate tensile test and ESSO test. The fracture toughness for crack initiation and propagation was evaluated quantitatively for the full thickness specimen. It was found that EH-36 grade steel with the thickness of 80mmt showed the KIC value of 164kgf/mm1.5 at -145°C. Also, large-scale ESSO test result showed that the steel with the thickness of 80mm had 520kgf/mm1.5 at -10°C. Although it was known that the fracture toughness decreases with the increase of the plate thickness, EH-36 grade steel with the thickness of 80mm had enough values of fracture toughness to prevent the crack initiation and arrest the brittle crack propagation.

Effect of Strength Matching and Strain Hardening Capacity on Fracture Performance of X80 Line Pipe Girth Welded Joint Subjected to Uniaxial Tensile Loading

Abstract By conducting curved wide plate tensile tests for girth welded joints of X80 line pipe containing a surface notch in the weld metal, the effects of strength matching on fracture performance were evaluated. Parametric studies were also conducted using a finite element method simulating the experiments to clarify the effects of strain hardening capacity of the base metal, softening in the heat affected zone, and groove configuration on fracture performance. A strain at failure significantly decreased with the decreasing strength matching. This was expected to be due to a difference in local straining behavior at the notch tip caused by the shielding effect. The analytical studies revealed that the strain hardening capacity of the base metal, the softening in the heat affected zone, and the groove configuration affected the allowable strain for a given toughness level in the case of overmatching. However, these factors hardly affected the allowable strain in the case of undermatching.

Effect of Strength Matching on Ductile Fracture Behavior of X80 Linepipe Girth Welds Subjected to Tensile Loading

This paper describes the effects of yield stress matching on the ductile fracture behavior of X80 linepipe girth welds. Three girth welded joints were made on an X80 linepipe using several consumables to obtain about a 20% yield stress overmatched, evenmatched and about a 20% undermatched weld metal. For these three welded joints, curved wide plate tensile tests were then conducted with a surface notch in the weld metal and the heat affected zone. The yield stress matching significantly affected fracture behavior and the ductile crack initiation, that is, the overmatched welded joint had a higher resistance to ductile fracture than that of the undermatched welded joint for both the weld metal and HAZ notch. The ductile crack initiation was successfully detected using a direct-current electric potential method. The allowable strength matching level could be determined using the relationship between the strength matching and the gauge length strain from the viewpoint of preventing the ductile crack initiation.