Large Plastic Deformation Research Articles

Reduced model for fracture of geometrically exact planar beam: Non‐local variational formulation, ED‐FEM approximation and operator split solution

SummaryIn this work, we present a novel reduced model for computing the solution to a bending fracture problem of the geometrically exact beam. The Reissner model is chosen for representing the large elastic and large plastic deformations of such a beam model. The non‐local variational formulation is proposed to deal with the softening phenomena characteristic of fracture. The fracture energy is introduced as the main fracture parameter, rather than (in general) ill‐defined characteristic length used for previous non‐local models. The discrete approximation is built in terms of the embedded‐discontinuity finite element method (ED‐FEM), which needs no initial crack for optimal performance nor detailed crack kinematics description, such as in the X‐FEM or the phase‐field approach. This kind of approach builds upon the best approximation property of the FEM discrete approximation in the energy norm and provides the best‐approximation property for the dissipated energy computations, and thus optimal computational accuracy if the quantity of interest is inelastic dissipation. The computations are carried out by the operator split method, which separates the computations of global state variables (displacements and stress) from local (internal) variables including the crack opening. Several illustrative examples are provided to confirm an excellent performance of the proposed methodology.

Exact solutions of burst pressure for thick-walled cylinders in power-law strain hardening steels

Exact solutions of burst pressure for defect-free, thick-walled cylindrical pressure vessels with capped ends are developed using the flow theory of plasticity in terms of the Tresca, von Mises, and Zhu-Leis yield criteria. The material is assumed to obey a power-law strain hardening rule, and the finite strain theory is adopted to describe large plastic deformation. On this basis, internal pressure is obtained as a complex polynomial function of effective strains on the inside and outside surfaces of the pressure vessel with the use of the Bernoulli numbers. At burst failure, the effective strains and stresses on the inside and outside surfaces are first determined, and then three flow solutions of burst pressure are obtained as a power series function of the diameter ratio (Do/Di), strain hardening exponent (n), and ultimate tensile stress (UTS). The power series solution is confirmed to agree well with the exact flow solution of burst pressure in a closed-form for each yield criterion, and the results show that the von Mises flow solution is an upper bound prediction, the Tresca flow solution is a lower bound prediction, and the Zhu-Leis flow solution is an intermediate prediction of burst pressure. Two sets of full-scale burst test data are then utilized to evaluate and validate the proposed flow solutions of burst pressure for both thin-walled pipes and thick-walled cylindrical pressure vessels.

Experimental investigation of influence parameters on cartridge fired pin resistance

AbstractCartridge fired pins, also known as powder actuated fasteners, have a wide application in different construction industry fields, mostly for joints of cold‐formed structural elements and profiled steel sheeting, or for installation of shear connectors in composite steel‐concrete structures. Installation of cartridge fired pins is mostly governed by high energy introduction from installation device and mechanical fastener to the steel base material, without initial predrilling of holes. Therefore, large plastic deformations of base material are developed through installation procedure, together with various anchorage mechanisms between fastener and base material. This paper presents experimental investigation of most important influence parameters on behaviour and resistance of cartridge fired pins, such as adjusted installation power level on installation device and steel base material strength. Experimental investigation involved X‐ENP‐21 HVB cartridge fired pins through double‐sided shear tests, tension tests with fasteners installed over X‐HVB shear connector with two different steel grades (S275 and S355) and two installation power levels (2 and 3.5), and tension tests with fasteners installed over two thicknesses of profiled steel sheeting (0.8 mm and 1.0 mm). Cartridge fired pin resistances together with corresponding failure mechanisms were experimentally quantified and presented in this paper.

Multiscale modeling of particle-induced damage in AA7075 aluminum sheet at large plastic strains

Large plastic deformation and ductile damage in precipitation hardening aluminum alloy AA7075 is driven by plastic flow in the vicinity of particles as well as fracture and decohesion of second phase particles embedded in the matrix. The current work investigates the deformation and damage characteristics of Fe-rich intermetallic particles, and η and θ precipitates in AA7075-O sheet. A multiscale model simulation methodology is presented and applied to analyze large-scale plastic deformation and damage characteristics. The methodology utilizes nanoscale molecular dynamics simulation to obtain matrix-particle interface strength properties and Weibull statistics to capture experimental fracture characteristics of particles. The above sub-models are incorporated within a 2-D real particle microstructure-based finite element model to conduct a comparative study of the roles of decohesion and fracture in the development of plasticity and void damage in AA7075-O sheet. In addition, in-situ SEM uniaxial tensile tests are carried out to assess the effectiveness of the simulation methodology and to compare the experimental and numerical results. Post-test high resolution X-ray computed tomography (HR-XCT) was also carried out to qualitatively observe particle-induced voiding in the material. The numerical methodology is shown to capture well the experimental trends in damage evolution of the individual particles. It is observed that particle damage is a function of inherent particle properties, their morphological features, and matrix strain localization characteristics. Larger-size Fe-rich particles are observed to undergo damage at an earlier stage, and consequently, affect the strain localization characteristics the most. In contrast, η precipitates are found to be most resistant to particle damage, followed by θ precipitates. Higher stresses inside strain localization bands, caused increased void damage initiation and growth of η and θ precipitates. Overall, particle fracture is observed to be marginally higher compared to particle decohesion, irrespective of the particle type.

Effect of In on Fe phase morphology and properties of Cu-Fe alloy

ABSTRACT In this paper, Cu-6.2Fe-xIn (x = 0, 0.2, 0.4) alloy was prepared by melting casting and mechanical heat treatment. The Fe phase morphology of Cu-6.2Fe-xIn alloy was observed by SEM, EBSD and TEM. The results show that the addition of In element refines the primary Fe phase and optimises its distribution. After large plastic deformation, the Fe phase was fibrillated and the addition of In refines the Fe fibre and increases its density. The strength of Cu-6.2Fe-0.4In alloy with strain of 7 were 901 MPa, which was 201 MPa higher than that of Cu-6.2Fe alloy. The refining effect of In on the primary Fe phase was the main reason for the significant improvement of the strength of Cu-Fe-In alloy.

ProCrackPlast: a finite element tool to simulate 3D fatigue crack growth under large plastic deformations

Many structural components and devices in combustion and automotive engineering undergo highly intensive cyclic thermal and mechanical loading during their operation, which leads to low cycle (LCF) or thermomechanical (TMF) fatigue crack growth. This behavior is often characterized by large scale plastic deformations and creep around the crack, so that concepts of linear-elastic fracture mechanics fail. The finite element software ProCrackPlast has been developed at TU Bergakademie Freiberg for the automated simulation of fatigue crack growth in arbitrarily loaded three-dimensional components with large scale plastic deformations, in particular under cyclic thermomechanical loading. ProCrackPlast consists of a bundle of Python routines, which manage finite element pre-processing, crack analysis, and post-processing in combination with the commercial software Abaqus . ProCrackPlast is based on a crack growth procedure which adaptively updates the crack size in finite increments. Crack growth is controlled by the cyclic crack tip opening displacement varDelta CTOD, which is considered as the appropriate fracture-mechanical parameter in case of large scale yielding. The three-dimensional varDelta CTOD concept and its effective numerical calculation by means of special crack-tip elements are introduced at first. Next, the program structure, the underlying numerical algorithms and calculation schemes of ProCrackPlast are outlined in detail, which capture the plastic deformation history along with the moving crack. In all simulations, a viscoplastic cyclic material law is used within a large strain setting. The numerical performance of this software is studied for a single edge notch tension (SENT) specimen under isothermal cyclic loading and compared to common finite element techniques for fatigue crack simulation. The capability of this software is featured in two application examples showing crack growth under mixed-mode LCF and TMF in a typical austenite cast steel, Ni-Resist. In combination with a crack growth law identified in terms of varDelta CTOD for a specific material, the tool ProCrackPlast is able to predict the crack evolution in a 3D component for a given thermomechanical loading scenario.

Modified Taylor Impact Tests with Profiled Copper Cylinders: Experiment and Optimization of Dislocation Plasticity Model.

Current progress in numerical simulations and machine learning allows one to apply complex loading conditions for the identification of parameters in plasticity models. This possibility expands the spectrum of examined deformed states and makes the identified model more consistent with engineering practice. A combined experimental-numerical approach to identify the model parameters and study the dynamic plasticity of metals is developed and applied to the case of cold-rolled OFHC copper. In the experimental part, profiled projectiles (reduced cylinders or cones in the head part) are proposed for the Taylor impact problem for the first time for material characterization. These projectiles allow us to reach large plastic deformations with true strains up to 1.3 at strain rates up to 105 s-1 at impact velocities below 130 m/s. The experimental results are used for the optimization of parameters of the dislocation plasticity model implemented in 3D with the numerical scheme of smoothed particle hydrodynamics (SPH). A Bayesian statistical method in combination with a trained artificial neural network as an SPH emulator is applied to optimize the parameters of the dislocation plasticity model. It is shown that classical Taylor cylinders are not enough for a univocal selection of the model parameters, while the profiled cylinders provide better optimization even if used separately. The combination of different shapes and an increase in the number of experiments increase the quality of optimization. The optimized numerical model is successfully validated by the experimental data about the shock wave profiles in flyer plate experiments from the literature. In total, a cheap, simple, but efficient route for optimizing a dynamic plasticity model is proposed. The dislocation plasticity model is extended to estimate grain refinement and volume fractions of weakened areas in comparison with experimental observations.

Fatigue behavior evaluation in Fe-20Mn-3Al-0.9C alloys by dynamic nanoindetation

The fatigue response by applying cyclic loads on individual grains using monotonic and cyclic nanoindetation to analyze the effect on load or displacement control in an austenitic Fe-20Mn-3Al-09C alloy were analyzed. The material response to the cycles considering the load control and the displacement control to properties such as hardness, elastic's modulus, and contact stiffness, was studied by analyzing the load-unload curves (P-h). The material softening Analysis showed that these properties decrease with increasing cycles due to the activation of deformation mechanisms. The elasticity's Modulus and hardness values for monotonic loads in load control presented values close to those reported in the literature. On the other hand, in displacement control, the values were lower. In load and displacement control mode, the first two cycles presented no overlap between unloading and loading between cycles, due to large irreversible plastic deformation and low elastic recovery after unloading. In the subsequent cycles, overlaps between the hysteresis curves were predominant, due to the activation of the deformation mechanisms.

High-temperature mechanical performance of Ru doped cermets

The mechanical properties degradation of cermets under high temperatures greatly limits their applications. In this paper, the compressive yield strength of WC-Co based cermets at high temperatures was significantly improved by the addition of Ru. Based on the detailed microstructure analyses, the contribution of Ru to the plastic deformation of the cermets was disclosed. The addition of Ru would stabilize the fcc-Co structure, leading to an increase in the proportion of the coherent WC/Co phase boundaries. The coherent phase boundaries are beneficial to avoid stress concentration across the interface and premature crack initiation, inducing higher dislocation densities and larger plastic deformation in both Co and WC phases. The solid solution strengthening effect of Ru and the Ru cluster in the Co phase can inhibit the softening of the binder phase at high temperatures. The synergy of solid solution strengthening and dislocation strengthening is responsible for the higher yield strength of WC-Co cermets with Ru at high temperatures.

Predicting the forming limits in the tube hydroforming process by coupling the cyclic plasticity model with ductile fracture criteria

This study presents a one-surface plasticity constitutive model combined with phenomenological and micromechanical damage models to be applied to the large plastic deformation during tube hydroforming. These factors lead to simulating the Bauschinger effect and transient behavior in large plastic strain ranges and predicting fracture onset. By using the integration approach, a numerical integration algorithm of implementation by explicit schemes was carried out. A comparison of several cyclic loading tests between experiments and numerical simulation was accomplished. The accuracy of these models is verified, which could be expanded to a large strain range forming process. Adopting the proposed models, finite element modeling is performed in the tube hydroforming process. The simulation and experimental results comparison showed that the proposed framework accurately predicted the tube formability in the hydroforming process.

Computational prediction of chevron cracking during multi-pass cold forward extrusion

The cold forward extrusion is a manufacturing process that is widespread in automated production due to its economic benefits. The cross-section is reduced during this process, which is accompanied by large plastic deformations. It may lead to the chevron cracking, which has to be predicted for flawless production and maintaining economic advantage. Therefore, the multi-pass cold forward extrusion of cylinder made from AISI 1045 was numerically simulated. The central cracks were predicted by the recently proposed uncoupled ductile fracture criteria. These were calibrated using various experiments, including the small punch test with additional fractographic observation. The material model was implemented into Abaqus using the user subroutine so that defects were successfully predicted using an element deletion technique.

Microstructural characterization and mechanical properties of Inconel 625 wall fabricated by GTAW-based WAAM using stringer bead and circular weave pattern

In this work, Inconel 625 alloy was used to manufacture walls using the Wire Arc Additive Manufacturing (WAAM) technology, which is based on Gas Tungsten Arc Welding (GTAW). The wall was fabricated using a circular weave and stringer bead pattern. Microstructural analysis and tensile characteristics were evaluated for both walls. Using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and elemental mapping, the fracture zones of the tensile specimens were examined. The microstructure is mostly made up of equiaxed dendrites, with the rare presence of continuous and discontinuous cellular dendrites along the cross-section. In tensile tests, circular weaved walls performed better than stringer bead walls. The circular weave specimen had an ultimate tensile strength (UTS) of 762 MPa in the horizontal and 722 MPa in the vertical orientations. Also, the Inconel 625 wall showed anisotropic behavior (5.3%) during tensile testing. The fracture morphology analysis revealed that all the specimens were fractured as a result of large plastic deformation, corresponding to ductile failure. Based on the EDS results, the fracture zone mainly consists of Ni and Cr with a small percentage of Nb and Mo. The absence of laves phases makes the fracture mode ductile. The elemental mapping shows uniform dispersion of Ni and Cr within the fracture region, further supporting the ductile failure mode.

Synchronous-hammer-forging-assisted wire arc additive manufacturing Al-Mg alloy

The plastic deformation-assisted wire arc additive manufacturing (WAAM) technology based on the hammer-forging method has essential application prospects in preparing high-dense fine-grain aluminum alloy components. However, the existing interlayer hammer-forging method has limitations, such as insufficient hammering force and high demand for hammering times when obtaining large plastic deformation. To effectively solve these problems, this paper proposed synchronous-hammer-forging-assisted WAAM technology and systematically studied its effects on the macroscopic morphology, microstructure, pores evolution, and mechanical properties of WAAM Al-Mg alloy specimens. The results show that under the synchronous hammer-forging (SHF) condition, a large plastic deformation of 33.97% can be achieved by the 80 N hammer forging force, and the surface flatness of the specimen was significantly improved. The grain size of the specimen was reduced from 105.92 µm in the deposited state to 37.15 µm in the hammered specimen by 64.93% with a significant equiaxed effect. Simultaneously, with the application of SHF technology and the increasing hammer-forging force, the precipitated phase dominated by Al3Mg2 was broken. The pores in the specimen changed from round to narrow and elongated shape with only 0.0065% porosity. The number of pores, equivalent diameter, and surface area were reduced by 68.33%, 13.75%, and 67.24%, respectively. The yield strength and ultimate tensile strength of the hammer-forged specimens reached 250.37 MPa and 315.03 MPa, respectively, which were 36.28% and 8.95% higher than those of the deposited specimens, and still maintained a high elongation rate of 36.11%.

Analysis of RC Multistory Building with and Without Blast Forces

Blast resistant and anti-terrorism design is essential in order to save the civil infrastructure and human lives. In the design of structures, a consideration for energy absorbing capabilities to resist the effects of blast loading or other severe dynamic loads it is vital, and structural provision of elements with large plastic deformation capacities is desirable. Structures need to be designed for ductile response in order to prevent partial or total collapse due to locally failed elements. The work in this paper considers theoretical studies to resist the structure against blast loading to understand the basic concept of explosion phenomena, parameters of blast loading, and different types of blast waves. The analysis focuses on the estimation of blast loading on structures and their response to explosions. Design of blast resistant structures requires thorough understanding of the structural dynamics, behaviour of materials under high strain rate of loading, and blast analysis. This paper concludes with an explanation of findings by different researchers using different country codes to simplify the design process for calculating blast load. Keywords: Blast Resistant Design, Blast Load, Explosion, ETABS.

Preparation of ultrafine-grained Nb-1Zr alloy by increasing the time of large plastic deformation during friction stir processing

The grain evolution mechanism of Nb-1Zr alloy during friction stir processing (FSP) was studied under three large plastic deformation conditions: high-temperature-short-time, high-temperature-long-time, and low-temperature-long-time. The niobium alloy grains can be continuously refined during processing. By increasing the time for large plastic deformation during friction stir processing, ultrafine-grained niobium alloys can be prepared with only a single pass of processing. To the best of the authors' knowledge, this phenomenon has been confirmed for the first time and can be used as an efficient processing strategy for grain refinement by FSP.

Analysis of ultimate seismic performance of thin-walled concrete-filled steel tube bridge piers under dynamic load

This study entailed the use of a cyclic loading test on a thin-walled concrete-filled steel tube (CFST) bridge pier to investigate its ultimate seismic performance. Additionally, a three-dimensional solid-shell finite element (FE) model of thin-walled CFST piers was established using ABAQUS. Cracks were introduced into in-filled concrete, and ductile damage was imposed on the steel tubes, in order to accurately reproduce the seismic performance degradation and post-earthquake residual displacement variation in thin-walled CFST bridge piers. The FE model was validated using pseudo-static and pseudo-dynamic loading tests performed on thin-walled CFST bridge piers. The analysis indicates that the FE model with concrete cracks can reflect the pinching effect of the hysteresis curve; the ductile damage can reflect the degradation of the bearing capacity during large plastic deformation under cyclic loading and the residual displacement under unidirectional and bidirectional dynamic loading. The seismic response of the full in-filled thin-walled CFST bridge pier was the least under the same intensity seismic wave, the in-filled concrete could improve ultimate seismic capacity. Finally, this study established a formula for the relationship between the residual and maximum displacements at the top of thin-walled CFST bridge piers under bidirectional seismic waves.

Exact solution of burst pressure for thick-walled pipes using the flow theory of plasticity

This paper develops an exact solution of burst pressure for defect-free, thick-walled pipes using the flow theory of plasticity in terms of the average shear stress yield criterion (or Zhu-Leis yield criterion). The pipe steel is assumed to obey the power-law strain hardening rule, and large plastic deformation is described by the finite strain theory. On this basis, internal pressure is obtained as a power series function of the effective strains on the inside and outside surfaces of the thick-walled pipe with use of the second Bernoulli numbers. At burst failure, the Zhu-Leis flow solution of burst pressure is determined as a power series solution, and the burst effective strains, the burst effective stresses, and the burst pressure are functions of the diameter ratio (Do / Di), strain hardening exponent (n), and ultimate tensile strength (UTS). Similarly, the Tresca and von Mises flow solutions of burst pressure are also determined as a power series solution in terms of the Tresca and von Mises yield criteria. A general closed-from exact solution of burst pressure is then proposed for the three yield criteria, and the results showed that the proposed exact solution matches well with the power series solution for each yield criterion. Moreover, the von Mises flow solution is an upper bound prediction, the Tresca flow solution is a lower bound prediction, and the Zhu-Leis flow solution is an intermediate prediction that agrees well with the finite element analysis results of burst pressure for thick-walled pipes. Two datasets of full-scale burst tests are then utilized to evaluate and validate the proposed flow solutions of burst pressure for both thin and thick-walled pipes.

Research on Plastic Deformation of Rolled Pieces of Four-power rolling Mill Based on Deform

Aiming at the problems of large cross-section size change and low shape and position accuracy of the workpiece rolled by the four-power rolling mill, based on analyzing the plastic deformation mechanism of metal crystals, the rolling simulation was carried out by deform software to analyze the variation of section plastic deformation height and equivalent stress distribution of the rolled workpiece section. The results show that under the action of mutual vertical rolling force, the large plastic deformation with a length of about 2mm occurs in the local area of 45 ° diagonal at the end of the section, and the maximum height dimension increases by 4.5% relative to the blank height dimension. Its equivalent stress at the ends of both sides of the section is also the largest, and then gradually decreases and tends to be stable.

Ceria-stabilized zirconia-based composites printed by stereolithography: Impact of the processing method on the ductile behaviour and its transformation features

A commercial composite powder was used to develop a new paste for stereolithography processing (SLA) of dense 11Ce-TZP-based composites containing 8 vol.% of alumina and 8 vol.% of strontium aluminate. The same powder was used to prepare reference ceramics by conventional Cold Isostatic Pressing (CIP) and sintering. The use of SLA gave rise to a microstructure containing larger strontium aluminate clustering surrounded by zirconia grains devoid of alumina particles, which appeared embedded in a matrix of zirconia-alumina grains. This slightly more heterogeneous microstructure favored the formation of a greater number of thinner transformation bands, causing a larger plastic deformation in SLA samples (failure strain of 0.65 % instead of 0.35 % for CIP samples), without compromising characteristic strength ( σ 0 = 560 and 586 MPa respectively) . Thus, SLA does not affect the ductile behaviour that characterizes this type of ceramics and appears as a very promising method for the development of custom-made ceramic prostheses.

Dynamic Behaviour of Selective Laser Melted 316L Steel - Mechanical Properties and Microstructure Changes

316L steel specimens with three different shear zones made by SLM (Selective Laser Melting) were subjected to dynamic tests using the Split Hopkinson Pressure Bar method. The effect of high-speed deformation on changes in microstructure was analyzed. In addition, the stress-strain relationship was determined from the SHPB results. To visualize the deformation process of the specimens during the tests, a camera with a high frame rate was used. It was shown that as the plastic deformation increases, the hardness of the material increases. Microstructural analysis of dynamically loaded areas revealed numerous defects. Twinning was found to be the main deformation mechanism. Large plastic deformation and many other microstructural changes such as shear bands, cracks and martensite nucleation were also observed.