Accumulation Of Plastic Deformation Research Articles

Experimental flexural behavior of SMA-FRP reinforced concrete beam

The most critical drawback in currently used steel reinforcement in reinforced concrete (RC) structures is susceptibility to accumulation of plastic deformation under excessive loads. Many concrete structures due to damaged (yielded) steel reinforcement have undergone costly repairs and replacements. This research presents a new type of shape memory alloy (SMA)-based composite reinforcement with ability to withstand high elongation while exhibiting pseudo-elastic behavior. In this study, small diameter SMA wires are embedded in thermoset resin matrix with or without additional glass fibers to develop composite reinforcement. Manufacturing technique of new proposed composite is validated using microscopy images. The proposed SMA-FRP composite square rebars are first fabricated and then embedded in small scale concrete T-beam. 3-point bending test is conducted on manufactured RC beam using a cyclic displacement controlled regime until failure. It is found that the SMA-FRP composite reinforcement is able to enhance the performance of concrete member by providing re-centering and crack closing capability.

Simulation on Stress Relaxation of DD3 Nickel-Based Single Crystal Superalloy Based on Micro-Cell Model

Tension-torsion experiments at 680°C and 850°C on thin-wall tube specimens of DD3 nickel-based single crystal superalloys were successfully completed. It shows that specimens have stress relaxation obviously and inelastic deformation accumulation phenomenon with different crystal orientation under asymmetric cyclic loadings. Based on the microstructure characteristics of nickel-based single crystal superalloys, a two-phase multi-cell microscopic mechanical model was established by finite element method to simulate the test with displacement. Numerical simulation studies showed that the matrix phase appeared plastic deformation accumulation at first and resulted in low cycle fatigue damage, but stress distortion occurred on the boundary with a single cell model under tension-torsion displacement loading, which is not consistent with experimental results. While using multi-cell model can avoid this phenomenon, it could be better to simulate stress relaxation behavior under asymmetric cyclic loading at elevated temperature and to study on stress weaken damage for single crystal superalloys.

The Plastic Deformation and Enhancement of 304Stainless Steel under Low Stress Repeat Impact

In engineering applications, many key components will fail with macroscopic accumulated plastic deformation, repeated impact loads, even though the stress is far less than the material yield limit. This kind of load can be called low stress repeated impact load in this study. It is observed that the plastic deformation of the material is mainly manifested in closer to the site from the collision surface. The strain decreases with the increasing depth from the surface, and it will be smaller and smaller with the increasing number of the impact. Finally, the strain tends to be stable, which means the material will no longer be deformed[1]. Take the method of preparation of the exponential gradient coating on 304stainless steel for performance enhancement, in order to satisfy and expand its application scope and conditions.

Effect of cyclic loading on the nanoscale deformation of hydroxyapatite and collagen fibrils in bovine bone

Cyclic compressive loading tests were carried out on bovine femoral bones at body temperature (37 °C), with varying mean stresses (-55 to -80 MPa) and loading frequencies (0.5-5 Hz). At various times, the cyclic loading was interrupted to carry out high-energy X-ray scattering measurements of the internal strains developing in the hydroxyapatite (HAP) platelets and the collagen fibrils. The residual strains upon unloading were always tensile in the HAP and compressive in the fibrils, and each increases in magnitude with loading cycles, which can be explained from damage at the HAP–collagen interface and accumulation of plastic deformation within the collagen phase. The samples tested at a higher mean stress and stress amplitude, and at lower loading frequencies exhibit greater plastic deformation and damage accumulation, which is attributed to greater contribution of creep. Synchrotron microcomputed tomography of some of the specimens showed that cracks are produced during cyclic loading and that they mostly occur concentric with Haversian canals.

Yield Characteristics of a Twill Dutch Woven Wire Mesh Via Experiments and Numerical Modeling

Woven structures are steadily emerging as excellent reinforcing components in composite materials. Metallic woven meshes, unlike most woven fabrics, show high potential for strengthening via classical methods such as heat treatment. Development of strengthening processes for metallic woven materials, however, must account not only for behavior of the constituent wires, but also for the interactions between contacting wires. Yield behavior of a 325 × 2300 stainless steel 316L (SS316L) twill dutch woven wire mesh is analyzed via experimental data and 3D numerical modeling. The effects of short dwell-time heat treatment on the mechanical properties of this class of materials is investigated via uniaxial tensile tests in the main weave orientations. Scanning electron microscopy (SEM) is employed to investigate the effects of heat treatment on contacting wire interaction, prompted by observations of reduced ductility in the macrostructure of the mesh. Finally, the finite element method (FEM) is used to simulate the accumulation of plastic deformation in the mesostructure of the mesh, investigating how this wire level plasticity ultimately affects global material yielding.

Elastic–plastic analysis of the steel-to-tungsten transition joint for a high performance divertor

The use of tungsten as a plasma-facing material necessitates a transition joint to the oxide dispersion strengthened (ODS) steel or ferritic steel (FS) structural material of the primary coolant loop at the end of the divertor target plate where the surface heat flux is very low. A critical issue in the transition joints is the coefficient of thermal expansion (CTE) mismatch between the tungsten (or tungsten-alloy) and ODS steel, which can lead to unacceptably high thermal stresses during steady state and ratcheting during cyclic loads. Detailed 2D and 3D thermo-mechanical analyses were conducted to study the behavior of a transition from tungsten to FS with an intermediate layer of tantalum, located outside of the high heat flux region. The results include plastic strains under various loading conditions including fabrication processes, warm and cold shutdown, and allow for plastic behaviors leading to stress relaxation. The accumulation of plastic deformation may cause ratcheting. Modifications were proposed to the transition joint design in order to eliminate stress concentration and ratcheting under cyclic loading. The results of the modified design exhibited less plastic deformation in the joints as well as no ratcheting caused by warm and cold shutdown.

Crack interaction with incrementally accumulated plastic deformation under nonstationary thermal actions

One of the failure modes of ductile structural elements undergoing repeated thermal loading is incremental collapse caused by strain accumulation. Another failure mode typical for such loading is the stable growth of long cracks, with the crack being able to achieve the size of thermal tension zone movement. The impact of general incremental deformation accumulation on cyclic crack growth under repeated thermal actions is studied in this paper. The computational interpretation of the experiment shows that the static damage resulted from overall incremental deformation accumulation exceeds the fatigue one caused by reversed plasticity. This fact proves that under severe thermal ratchetting a crack can be driven mostly by a quasistatic opening produced by the strain accumulated within a body rather than by fatigue.

Investigation on the fretting fatigue behaviors of steel wires under different strain ratios

The fretting fatigue tests of steel wires were performed on the self-made fretting fatigue test equipment under different strain ratios ranging from 0.90 to 0.70 with contact loads of 50N and 70N. Curves of Ft–D–N were drawn, and the dissipated energy was calculated through the curves of Ft–D. Morphological features of fretting scar and fracture surface were observed by scanning electron microscopy (SEM). The results reveal that as the strain ratio decreased, the fretting regime changed from partial slip regime to mixed regime and slip regime. Shorter fretting fatigue life, higher wear coefficient were induced by a lower strain ratio. The curves of dissipated energy corresponding to three kinds of fretting regimes were different from each other. Morphologies of adhesive wear, abrasive wear and fatigue wear as well as accumulation of plastic deformation and micro-cracks were observed in fretting scars. All fatigue fractures in different fretting regimes could be divided into three regions.

OS1418 円筒容器の応力再配分と熱ラチェット現象の基本メカニズムに関する研究

Under elevated temperature condition, thermal ratchet phenomena, namely the cyclic accumulation of plastic deformation, is one of the typical failure modes. Ratchet phenomena occurs when the structures are subjected to uniform primary stress with cyclic secondary stresses. ASME boiler & pressure vessel code provides an evaluation method for thermal ratchet. However, this method is so focused on protecting thermal ratchet, that it could be too conservative under some conditions. Therefore, the rational evaluation method for thermal ratchet phenomena is needed based on its mechanism. In this paper, rational simplified evaluation method for cylindrical vessels is proposed using simplified model called "two bar model", which express stress redistribution mechanism of cylindrical vessels. This evaluation method enables simple prediction of both thermal ratchet occurrence and thermal ratchet deformation.

Tests of Buckling-Restrained Braces Using Low-Yield Point Steel as Core Material

In order to reduce seismic responses of structures, low-yield point steel has been used for dampers due to its excellent energy dissipation capacity. However, few researches about the low-yield point steel dampers have been conducted in China so far. This paper mainly presents an experimental study on two buckling-restrained braces (BRBs) which take an in-line steel plate as the core and a double-web wide flange steel member as the outer unit. Low-yield point steel LY100 is taken as the core material and conventional steel SN400 is taken as the outer material. Uniaxial cyclic loading tests of two low-yield point steel BRBs (LYS-BRB) were conducted to investigate their hysteretic behavior and energy dissipation capacity. The two LYS-BRBs yielded at rather small displacement and their accumulated plastic deformation ratios reached 1639 and 1437, respectively. Significant strain-hardening behavior can be observed in the hysteresis curves of LYS-BRBs and the maximum cyclic stress reached 3.85 times the yield stress.

Micro-mechanism of rolling contact fatigue in Hadfield steel crossing

The formation of the fatigue cracks was due to massive vacancy clusters in the subsurface layer of Hadfield steel crossing, which are induced by the accumulated plastic deformation under the conditions of impact and contact stresses from train wheels. The high concentration layers of vacancy clusters were formed parallel to the working surface of the crossing, which caused the initial rolling contact fatigue cracks to be parallel to the working surface with a laminar distribution in the depth direction. It can be predicted that metals containing elements with larger atomic diameter should have better rolling contact fatigue and wear performances.

Hypoplastic model for sands with loading surface

Although the hypoplastic models for sands have exhibited good predictive capability in monotonic loading, they are not able to reproduce memory effects and predict excessive plastic accumulation under cyclic loading. To overcome these issues, a loading surface has been incorporated into a hypoplastic model. This surface is capped and has two hardening variables. Notions from the bounding surface plasticity were borrowed in order to formulate the hardening functions. With this novel model, some salient features can be described: the model can account for the accumulation of plastic deformation, a memory effect is provided by the new surface, and stress-induced anisotropy effects observed in sands are successfully simulated. A short calibration guide of the parameters is given, and some simulations for Hostun RF loose sand and Toyoura sand are presented.

A J2‐plasticity model based on bounding surface concept

SummaryThis article presents the development of a J2 small strain plasticity model based on bounding surface concept, along with numerical examples to demonstrate model behaviors and identification of model parameter using laboratory test data. The model is motivated by the need for simulating permanent deformation accumulation of asphalt concrete mixtures, which leads to rutting in flexible pavements under repeated traffic loading. The proposed model accounts for the observation that rutting is mostly caused by shearing and takes advantage of the fact that bounding surface concept allows for the progressive accumulation of plastic deformation under constant amplitude loading condition. Analytical solutions are given for typical laboratory testing conditions. The model can be calibrated using repeated simple shear test data that are typically available for asphalt concrete mixtures. It is shown that the model is easy to use and provides a promising alternative for modeling permanent deformation accumulation in materials subjected to repetitive (cyclic) loading. Copyright © 2012 John Wiley & Sons, Ltd.

Analysis of applying isotropic and anisotropic destruction criteria in simulating the destruction of anisotropic materials

A comparison of the results of the numerical simulation of anisotropic material destruction (using the example of the D16T aluminum alloy) at dynamic loading obtained using isotropic and anisotropic destruction criteria is presented. The Mises-Hill destruction criterion allowing for the anisotropy of a material’s ultimate strength is used as an anisotropic criterion of destruction. For the sake of comparison, the destruction of an anisotropic material at 6.5% accumulated plastic deformation is simulated as well.

Dynamic Test and Constitutive Model of 225 MPa Low Yield Point Steel Material and its Energy Absorption Ability

Based on Low Yield Point (LYP) steel's attractive features, e.g. relative lower yielding strength, better plasticity performance than traditional structural steel material, the feasibility of utilizing LYP steel material for absorbing blast and impact/shock energy through its plastic deformation is discussed in this paper. Selected 225 MPa class LYP steels made by Chinese An Gang Corp., abbreviated as AQ225, are tested via quasi-static and split Hopkinson pressure bar (SHPB) experiments, respectively. Then, Johnson-Cook dynamic constitutive model is developed through a comprehensive thorough processing of raw test data. Moreover, the reliability of achieved model and its corresponding parameters are discussed. Finally, the dynamic response of a square plate structure made of LYP steel as well as other different types of steel materials, e.g. high-strength HQ600 and normal high-strength low alloy steel Q345, subject to explosive loading is studied through numerical simulations. As a result, the advantages of LYP steel for absorbing blast and impact energy through the accumulated plastic deformation are demonstrated, which provides the basis of utilizing such material for protective structures.

Comportamento mecânico de pavimentos flexíveis submetidos a gradientes térmicos

Palavras-chave: pavimento flexivel, analise mecanistica, gradiente termico. ABSTRACT. Mechanical behavior of flexible pavements undergoing thermal gradients. The proper structural understanding of a pavement should consider, according to the pavement mechanics, the aspects related to the traffic load, the environment and material properties. When asphaltic materials are used, the stress/strain relationships and the dependencies of load-time and temperature are key parameters for understanding flexible pavement performance. In this study, we employed the finite elements method to calculate stress/strain in flexible pavements structures considering temperature variation. The input data includes material stiffness, which is function of temperature and changes with position and time. The pavement temperature is obtained through the heat transfer differential equation, applying the Laplace transform and its numerical inversion. The finite elements grid was generated by the software ANSYS ® and imported by the software MATLAB ® . In order to determine the stiffness of the first layer (asphalt concrete) we used the average of four nodes, depending on the each node temperature. The result evidences the importance of thermal gradients for the pavement analysis, both for the fatigue cracking and the accumulation of plastic deformations. The use of unique modulus for asphalt concrete layer generates results far from reality.

Dry sliding tribological properties of nanostructured copper subjected to dynamic plastic deformation

Dynamic plastic deformation (DPD) technique was used to synthesize a bulk nanostructured Cu sample with nano-scale twin bundles (about 1/3 in volume) embedded in nano-sized grains. Dry sliding friction and wear tests of ball-on-plate contact configuration were carried out for the DPD and the coarse grained (CG) Cu samples. The longitudinal-sectional observations of wear track were performed to character the subsurface microstructure of two kinds of Cu samples. Experimental results show that the DPD Cu exhibits an enhanced wear resistance relative to that of the CG Cu under a certain sliding condition. There is an obvious difference in subsurface microstructural evolution between the DPD and CG Cu during wear process. For the CG Cu, plastic deformation induced grain refinement plays an important role, and dynamic recrystallization follows after a large plastic deformation accumulation. However, for the DPD Cu sample, dynamic recrystallization can be observed in the initial sliding and subsequent plastic deformation generates gradually. (C) 2011 Elsevier B.V. All rights reserved.

Research on the Rotational Fretting Wear of Ti6Al4V Alloy against Silicon Nitride

The rotational fretting of Ti6Al4V titanium alloy flat against silicon nitride (Si3N4) ceramics ball has been investigated by using a special rotational fretting wear test rig. Under various parameters of normal load and angular displacement amplitude, three fretting regimes were observed (i.e. partial slip regime, mixed fretting regime, and slip regime), corresponding to the different evolutions of the running condition at the contact interface. The micro-examination of the wear scars revealed an accumulation of plastic deformation within the centre of the wear scars in the gross slip condition. The damage mechanisms in the different fretting regimes were analysed in detail. The results showed that the mechanisms were quite different in the different fretting regimes.

Lifetime Assessment of Load‐Bearing Polymer Glasses: An Analytical Framework for Ductile Failure

AbstractThe most widespread application of polymers in structural applications is their use as pipe material for e.g., gas distribution systems. Pipes have a design lifetime of typically 50 years, which rules out real‐time lifetime assessment methods. Here, an engineering approach is presented, which makes it possible to predict long‐term ductile failure of loaded glassy polymers based on short‐term tests. The approach is based upon the hypothesis that failure is governed by accumulation of plastic deformation up to a critical strain. A pressure‐modified Eyring relation is employed to calculate the accumulation of plastic strain for any simple loading geometry. It is demonstrated that the approach can produce accurate quantitative time‐to‐failure predictions for loaded PC specimens and uPVC pipe segments.magnified image

Modeling elasto-plastic indentation on layered materials using the equivalent inclusion method

This paper develops a fast semi-analytical model for solving the three-dimensional elasto-plastic contact problems involving layered materials using the Equivalent Inclusion Method (EIM). The analytical elastic solutions of a half-space subjected to a unit surface pressure and a unit subsurface eigenstrain are employed in this model; the topmost layer is simulated by an equivalent inclusion with fictitious eigenstrain. Accumulative plastic deformation is determined by a procedure involving an iterative plasticity loop and an incremental loading process. Algorithms of the fast Fourier transform (FFT) and the Conjugate Gradient Method (CGM) are utilized to improve the computation efficiency. An analytical elastic solution of layered body contact ( O’Sullivan and King, 1988) and an indentation experiment result involving a layered substrate ( Michler et al., 1999) are used to examine the accuracy of this model. Comparisons between numerical results from the present model and a commercial FEM software (Abaqus) are also presented. Case studies of a rigid ball loaded against a layered elasto-plastic half-space are conducted to explore the effects of the modulus, yield strength, and thickness of the coating on the hardness, stiffness, and plastic deformation of the composite body.