Complex Deformation Behavior Research Articles

A new approach to the determination of plastic flow stress and failure initiation strain for aluminum alloys cutting process

Abstracts Material flow stress in cutting is difficult to measure experimentally due to the complex deformation behavior involved. In this work, a finite element (FE) simulation of cutting and a theoretical flow stress model including plastic and failure criteria were developed to determine the flow stress during aluminum alloy (7075-T6) cutting process. In a stable plastic stage, the Johnson–Cook model considering the adiabatic temperature rise (ATR) was proposed to calculate the plastic flow stress, and the relative errors of the calculated and FE simulated stresses were less than 4%. In the ductile failure stage, an improved failure initiation criterion in terms of temperature, pressure and strain rate was proposed to determine the failure initiation strain in cutting. In addition, an energy-density based ductile failure criterion was used to predict the flow stress in the failure stage. By combining the proposed theoretical model results and the FE simulation results, the entire flow stress during cutting was obtained. The influence of the failure initiation strain of the chip layer on cutting performance was also discussed. In addition, a set of aluminum alloy (A2024-T351) orthogonal cutting simulations were performed to validate the effect of the failure initiation strain on the cutting process. The predicted variation trends of the failure initiation strain for the two types of aluminum alloys were similar, and the predicted forces and tool–chip contact lengths were compared with the measured values in Atlati et al. [9]. Finally, the prediction of the failure initiation strain and its influence on tool–chip contact behavior were validated indirectly.

Numerical study on the X80 UOE pipe forming process

The UOE process is an effective approach for manufacturing large-diameter submerged-arc welding pipes used in oil and gas pipelines. A UOE process comprises the successive procedures of crimping, U-forming, O-forming, joining, welding, and expanding. In this study, a two-dimensional finite element model of UOE forming process is established and all the forming stages of an X80 high strength steel pipe are numerically studied. A kinematic hardening model is incorporated in FEM to describe the Bauschinger effect of X80 steel. The formation mechanism of O-forming open-seam is unveiled based on analysis of the complex deformation and springback behaviors of plate under loading–unloading–reverse loading condition. The validity of the model established is demonstrated by comparing the calculated result and practical measurement. Furthermore, the influence of processing parameters, friction coefficient and material properties on open-seam and ovality are numerically investigated.

Invited Presentation: Electrochemically Induced Stresses in Energy Related Materials

The volume changes that are associated with composition changes in a solid can induce significant stresses, when these expansions or contractions are physically constrained. These phenomena are important in a variety of energy-related materials, where they lead to complex interactions between electrochemical and mechanical driving forces. We have employed in situ measurements of these stresses along with a variety of other in situ and ex situ characterization methods, to obtain critical information about how the relevant mechanisms operate in different types of materials. One example is ceria electrolytes in solid oxide fuel cells, where oxygen potential gradients across the electrolyte can lead to large stresses. These stresses, caused by differences in the oxygen content of the ceria, are significantly enhanced by grain boundary contributions that can be interpreted with space charge effects. In Li ion battery (LIB) electrodes, Li insertion and removal can also lead to very large stresses and complex deformation behavior. One area of interest here is the solid-electrolyte interphase (SEI) layer, where we have recently shown that substantial near-surface stresses occur during SEI formation on graphitic carbon anodes. These results imply that stresses can be engineered during SEI formation, to enhance the stability of these critical passivation layers. Another concern in is the mechanical integrity of interfaces in composite electrode structures. Here, we have used patterned thin film structures to understand the response of bi-material interfaces during Li cycling. The integrity of these interfaces is critical for cycling stability and capacity retention in rechargeable Li ion batteries.

Survival Life Analysis of the Cutting Tools During Turning Titanium Metal Matrix Composites (Ti-MMCs)

Metal matrix composites (MMCs), as a new generation of materials; have proven to be viable materials in various industrial fields such as biomedical and aerospace. In order to achieve a valuable modification in various properties of materials, metallic matrices are reinforced with additional phases based on the chemical and/or physical properties required in the in-service operating conditions. The presence of the reinforcements in MMCs improves the physical, mechanical and thermal properties of the composite; however it induces significant issues in the domain of machining, such as high tool wear and inferior surface finish. The interaction between the tool and abrasive hard reinforcing particles induces complex deformation behaviour in the MMC structure. Sever tool wear is technically the most important drawback of machining MMCs.In this study a statistical model is developed to estimate the mean residual life (MRL) of the cutting tool during machining Ti-MMCs. Initial wear, steady wear and rapid wear regions in the tool wear curve are regarded as the different states in the statistical model. Hence, the valuable information regarding the estimated total time spent in each state, called the sojourn time, and the transition times between the states are obtained from the model.In this paper the standard cutting conditions, based on the recommendation of the tool supplier, are adopted. Based on a Weibull model, the reliability and hazard functions are obtained and are utilized in order to calculate the MRL and the sojourn times.

Numerical investigation into the fragmentation efficiency of one coal prism in a roller pulveriser: Homogeneous approach

The aim of this paper is to numerically model the rolling compression induced breakage process of a single coal prism in a roller pulveriser and to quantify the resultant fragmentation efficiency. A coupling approach of the finite element method (FEM) and the smoothed particle hydrodynamics (SPH) method is adopted to examine the complete deformation and progressive fragmentation process involved. A coupled damage-plastic material model is used to simulate the complex deformation and failure behaviour of coal materials. In order to quantify the geometric properties of main fragments by the rolling compression, a numerical approach is developed based on the union-find algorithm. Parametric studies have been conducted considering various factors, including the geometric factors of prismatic coal specimens and the rotating velocity of the rigid roller. Typical modelling results are provided and the fragmentation efficiency is examined and discussed with respect to the corresponding factors.

An extended homogenous yield function based anisotropic hardening model for description of anisotropic hardening behavior of materials

Except for the Bauschinger effect and permanent softening, work hardening stagnation and cross-effect are often observed deformation behaviors for sheet metals subjected to strain path changes. These complex deformation behaviors are assumed to have great effect on the sheet forming process and the following spring back. To constitutively, and more precisely model these plastic behaviors, extensive models have been successfully developed. Particularly, the combined isotropic-kinematic hardening model is powerful to capture the plastic behavior of sheet metals during forward and reverse loading. However, there is strong coupling between anisotropic yielding and anisotropic hardening with the kinematic hardening. Recently, Barlat et al. (2011) [61] proposed a homogenous yield function based anisotropic hardening model to describe the Bauschinger effect, which is not formulated with the kinematic hardening rule. In the present work, the original anisotropic hardening model is extended to capture the often observed cross-effect during multi-stage loading and work hardening stagnation during reverse loading. Although only four coefficients are newly introduced in the extended model, it can capture well the main trends of work hardening stagnation and cross-effect. The capability of this extended model is demonstrated with applications to two materials, namely, high strength steel and mild steel DC06.

Prediction of flow stress in a wide temperature range involving phase transformation for as-cast Ti–6Al–2Zr–1Mo–1V alloy by artificial neural network

The isothermal compressions of as-cast Ti–6Al–2Zr–1Mo–1V titanium alloy in a wide temperature range of 1073–1323K and strain rate range of 0.01–10s−1 with a reduction of 60% were conducted on a Gleeble-1500 thermo-mechanical simulator. The flow stress shows a complex non-linear intrinsic relationship with strain, strain rate and temperature, meanwhile the strain-softening behavior articulates dynamic recrystallization mechanism in α phase, dynamic recovery mechanism in β phase and their comprehensive function during phase transformation (α+β). Based on the experimental data, an artificial neural network (ANN) was trained with standard back-propagation learning algorithm to generalize the complex deformation behavior characteristics. In the present ANN model, strain and temperature were taken as inputs, and flow stress as output. A comparative study has been made on ANN model and improved Arrhenius-type constitutive model, and their predictability has been evaluated in terms of correlation coefficient (R) and average absolute relative error (ARRE). During α, α+β and β phase regime, R-value and ARRE-value for the improved Arrhenius-type model are 0.9824% and 6.02%, 0.9644% and 21.02%, and 0.9627% and 12.38%, respectively, while the R-value and ARRE-value for the ANN model are 0.9992% and 0.91%, 0.9996% and 1.47%, and 0.9975% and 2.17%, respectively. The predicted strain–stress curves outside of experimental conditions articulate the similar intrinsic relationships with experimental strain–stress curves. The results show that the feed-forward back-propagation ANN model can accurately tracks the experimental data in a wide temperature range and strain rate range associated with interconnecting metallurgical phenomena, and in further it has a good capacity to model complex hot deformation behavior of titanium alloy outside of experimental conditions.

Characterisation and numerical modelling of complex deformation behaviour in thermally bonded nonwovens

A complex time-dependent deformation and damage behaviour in polymer-based nonwovens are analysed under conditions of multi-stage uniaxial loading. Elastic–plastic and viscous properties of a polypropylene-based fabric are obtained by series of tensile, creep and relaxation tests performed on single fibres extracted from the studied fabric. These properties are implemented in a finite-element (FE) model of nonwoven with direct introduction of fibres according to their actual orientation distribution in order to simulate the rate-dependent deformation up to the onset of damage in thermally bonded nonwovens. The predictions of FE simulations are compared with the experimental data of multi-stage deformation tensile tests and a good agreement is obtained including the mechanisms of deformation. Due to direct modelling of fibres based on their actual orientation distribution and implementation of viscous properties, the model could be extended to other types of polymer-based random fibrous networks.

튜브 스피닝 공정에서 성형깊이가 컵형 튜브의 변형거동에 미치는 영향

The aim of this study was to investigate the effects of forming depth on the deformation behavior of cup-like tubes made of AISI1020 steel in tube spinning process. Spinning process was performed on cup-like tubes, which had an inner diameter of 34mm and thicknesses of 7, 8.5 or 11.5mm. The forming depths achieved were 3, 4, and 5.5mm. The complex deformation behaviors occurring during the tube spinning process was explained using the experimental results. Also analyzed were the causes of the material buildup and the bulge defect of inner surface, observed on cross section of tubes. The relationship between tube spinning conditions and the height of bulge defect was examined. The results indicate that bulge defect is increased with a decrease of the forming depth. Moreover, a critical forming depth exists for preventing the generation of the bulge defect in the tube spinning process. The present results will be useful for future decisions of forming depths for successful tube spinning of cup-like tubes.

Numerical prediction of thermal panel distortion in automotive paint shop

Challenging automotive design in the face of modern lightweight strategies for weight reduction as well as legislative regulations, impose higher requirements for future car body development. This trend has led to the use of thinner sheet metal blanks and implies the need for narrow process windows especially within the coating process where thermal loads might cause local shape deviations. Moreover, developments in multimaterial design induce material configurations with complex deformation behaviour due to different expansion characteristics. For this reason, there is a need to improve the numerical prediction of surface quality in the early car development process. This paper deals with the effect of thermomechanical material properties relating to the final part characteristics, whereby the influence of time and heat dependent material properties affecting the yield point and flow characteristics is shown. In further investigations, the influence of initial yield strength, pre-stretching and subsequent thermal loads to the final yield strength is dealt with.

Multi-Length Scale-Enriched Continuum-Level Material Model for Kevlar®-Fiber-Reinforced Polymer-Matrix Composites

Fiber-reinforced polymer matrix composite materials display quite complex deformation and failure behavior under ballistic/blast impact loading conditions. This complexity is generally attributed to a number of factors such as (a) hierarchical/multi-length scale architecture of the material microstructure; (b) nonlinear, rate-dependent and often pressure-sensitive mechanical response; and (c) the interplay of various intrinsic phenomena and processes such as fiber twisting, interfiber friction/sliding, etc. Material models currently employed in the computational engineering analyses of ballistic/blast impact protective structures made of this type of material do not generally include many of the aforementioned aspects of the material dynamic behavior. Consequently, discrepancies are often observed between computational predictions and their experimental counterparts. To address this problem, the results of an extensive set of molecular-level computational analyses regarding the role of various microstructural/morphological defects on the Kevlar® fiber mechanical properties are used to upgrade one of the existing continuum-level material models for fiber-reinforced composites. The results obtained show that the response of the material is significantly affected as a result of the incorporation of microstructural effects both under quasi-static simple mechanical testing condition and under dynamic ballistic-impact conditions.

Competing elastic and adhesive interactions govern deformation behaviors of aligned carbon nanotube arrays

Recent experiments have revealed diverse and sometimes conflicting deformation behaviors of vertically aligned carbon nanotube arrays under compression, but a thorough understanding of this phenomenon is still elusive. Here, we employ a mesoscale bead-spring model to demonstrate that the seemingly complex deformation behaviors of carbon nanotube arrays can be understood from competing elastic and adhesive interactions at the micro scale.

Ab initiobased empirical potential used to study the mechanical properties of molybdenum

Density-functional theory energies, forces, and elastic constants determine the parametrization of an empirical, modified embedded-atom method potential for molybdenum. The accuracy and transferability of the potential are verified by comparison to experimental and density-functional data for point defects, phonons, thermal expansion, surface and stacking fault energies, and ideal shear strength. Searching the energy landscape predicted by the potential using a genetic algorithm verifies that it reproduces not only the correct bcc ground state of molybdenum but also all low-energy metastable phases. The potential is also applicable to the study of plastic deformation and used to compute energies, core structures, and Peierls stresses of screw and edge dislocations. Molybdenum's high strength and high-temperature stability make this refractory metal very attractive for use in advanced process technologies. The motion of dislocations is generally accepted to be responsible for the complex deformation behavior of this transition metal. 1-8 In recent years progress has been made on the description of the properties of screw dislocations using density-functional theory (DFT), tight- binding calculations, and empirical potentials. 9-19 However, DFT and tight-binding techniques are limited to small system sizes, which is problematic due to the long-range strain field of dislocations, and current empirical potentials lack the required accuracy for the description of the dislocation structure. Simulations of dislocation motion and interactions require efficient interatomic potentials which accurately describe the dislocation energies, core structures, and motion. In this work we develop an empirical potential for Mo which predicts the ideal shear strength, generalized stacking fault en- ergies, energies of dislocations, and the Peierls stress and core structure of the � 111� /2 screw dislocation. The potential form is given by the modified embedded-atom method (MEAM) and the potential parameters are optimized usingabinitio energies, lattice parameters, forces, and elastic constants. Section II describes the calculations for the DFT database, the functional form of the MEAM potential, and the optimization of the potential parameters to the DFT database. The accuracy of the potential for structural, elastic, and defect properties is verified in Sec. III by comparison to DFT results and experiments. A genetic algorithm search of the energy landscape of the MEAM potential confirms that the potential reproduces the correct bcc ground state and predicts several low-energy metastable structures whose energies agree well with DFT results. Results of the MEAM potential for formation energies of point defects, phonon dispersion, thermal expansion, surface energies, ideal shear strength, and generalized stacking faults for the MEAM potential closely match DFT results and available experimental data. In Sec. IV we apply the potential to determine energies and Peierls stresses of the screw and edge dislocation in bcc Mo. The results show that the MEAM potential accurately describes the structural and mechanical properties of Mo and should be applicable to simulate the motion of dislocations and the plastic deformation of Mo.

Enhanced Requirements for Surface Quality of Outer Car Body Shells According to Thermal Manufacturing Processes

Challenging automotive design in the interaction of modern lightweight strategies to reduce car body weight as well as legislative regulations, impose higher requirements for future car body development. This trend leads to thinner sheet metal blanks and indicates higher requirements for narrow process windows in the entire manufacturing process to ensure the surface quality of outer shell panels. Especially, thermal loads within the coating process might cause local shape deviation in the startup phase of a new product. Further developments in multi-material-design for car body components induce material configurations with a complex deformation behavior due to different thermal expansion characteristics of the materials involved. For these reasons, there is a need to improve the prediction of the surface quality in the early car development process using numerical simulation methods. The influence of process parameters affecting the surface quality is shown and integrated into the process simulation.

Nanomechanical Properties of Advanced Plasma Polymerized Coatings for Mechanical Data Storage

In this paper we report on the unprecedented deformation behavior of stratified ultrathin polymer films. The mechanical behavior of layered nanoscale films composed of 8-12 nm thin plasma polymerized hexamethyldisiloxane (ppHMDSO) films on a 70 nm thick film of polystyrene was unveiled by atomic force microscopy nanoindentation. In particular, we observed transitions from the deformation of a thin plate under point load to an elastic contact of a paraboloid of revolution, followed by an elastic-plastic contact for polystyrene and finally an elastic contact for silicon. The different deformation modes were identified on the basis of force-penetration data and atomic force microscopy images of residual indents. A clear threshold was observed for the onset of plastic deformation of the films at loads larger than 2 μN. The measured force curves are in agreement with an elastic and elastic-plastic contact mechanics model, taking the amount of deformation and the geometry of the layer that presumably contributed more to the overall deformation into account. This study shows that the complex deformation behavior of advanced soft matter systems with nanoscale dimensions can be successfully unraveled.

Dynamic nanoindentation of articular porcine cartilage

Articular cartilage is a poroelastic (biphasic) material with a complex deformation behavior, which can be considered elastic–viscoelastic. In this article, articular porcine cartilage is tested in vitro using dynamic nanoindentation and is analyzed using the frequency domain. The testing and data analysis are presented as a function of the strain rate and frequency, which allows for the results to be compared for various load amplitudes over the same frequency range. In addition, a new approach to correct the contact area during dynamic nanoindentation is presented and the effects of sample freezing on the mechanical properties are also discussed.

A multiple-bundle model to characterize the mechanical behavior of the cruciate ligaments

Measurements of elongations of the cruciate ligaments have been used to study the behaviors of these ligaments in-vitro and in-vivo, mostly based on simplified two-bundle models of the cruciates. The complex fiber anatomy of the cruciates may suggest a complex deformation behavior across the continuum of their substance that cannot be captured by only two measurement points. In this study, a new methodology was introduced to include more detailed fiber anatomy and to take into consideration the wrapping of the PCL around the intercondylar notch of the femur in deep flexion. The method was used in comparison to the conventional two-bundle models on three sample cadaver knees that underwent a passive flexion up to 150°. The elongation ratios of the bundles were measured as the ratio of change in the length of the bundles over their lengths at 0° flexion. The multiple-bundle models showed ranges of variations across the attachment sites of the cruciates which at all flexion angles were significantly larger than those observed from the conventional two-bundle models. When expressed in percentages, at 150° flexion the ranges of variations in the elongation ratio of the bundles were 32.7% ± 31.9% and 34% ± 8.6% for the ACL and PCL, respectively. Results of this study showed that important variations of elongation across the body of the cruciates can be obscured to the conventional two-bundle model of the cruciates, and therefore a more detailed bundle configuration is suggested for the purpose of studying elongation behaviors of these ligaments.

3D Observation and Image-Based Finite Element Analyses of Fatigue Crack Propagation in an Al-Mg-Si Alloy

3D fatigue crack opening and propagation behaviors in an Al-Mg-Si alloy have been investigated in this study. A combined methodology of an in-situ 3D crack visualization via the synchrotron X-ray CT and image-based numerical simulation which takes into account real crack morphology has been applied for the study. The details of a crack with non-planar torturous crack morphology have been observed and many essential features of the crack and its opening/propagation inside the material have been identified. Typical example would be the complex deformation behaviors in the region where two crack segments lying on different horizontal planes overlap each other, and the influence of complicated crack front line on local crack driving forces. We recognized that two overlapping crack segments affected significantly the local crack driving force ΔkI each other, and large mode III displacement occurred near the edge of overlapping region. The region next to overlapping was influenced to a relatively large extent through shielding the near-tip stress/strain fields thereby reducing the local crack driving forces. We also found that the sharp extrusion on crack front line had no significant influence on neighboring cracks. The combined methodology of the in-situ 3D crack visualization and the image-based numerical simulation has been demonstrated to be powerful and feasible in revealing and understanding various fracture phenomena inside materials

Modeling and simulation of the microstructural behaviour in thermal sprayed coatings

AbstractThe purpose of the current work is the investigation of the mechanical behavior of thermal sprayed coatings to predict the influence of the application of compaction on the coatings. Due to the porosity and the poor surface quality of thermal sprayed coatings, an additional process step is necessary to compact the coating and to increase the surface quality, though leading to a complex deformation behavior of the coating. In a first step the microstructural evolution is investigated. Due to the fact that the experimental determination of the mechanical properties of a coating is quite complicated and cost‐intensive, a general procedure is developed which generates the desired quantities for different coating composites from microstructural images which are compared to analytical mean‐field homogenization solutions for elastic material behavior. The discussed thermal sprayed coatings are multiphase systems consisting of a metal‐matrix composite with pores. (© 2009 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modeling dislocation structure development and creep–swelling coupling in neutron irradiated stainless steel

Anisotropic nucleation and growth of multi-classes of dislocation loops under the combined actions of fast-neutrons and an external applied stress are considered in modeling dislocation structure development in metals and alloys. The stochastic nature of the nucleation kinetics is formulated via the Fokker–Planck equation. The strain derived from the climb of the anisotropic dislocation structure is separable into volumetric and deviatoric components, corresponding respectively to swelling and creep. The creep contribution resulting from the development of the stress-induced dislocation anisotropy is found to be very significant and exhibits a strong correlation with swelling. For stainless steel, our model explains very well the complex deformation behavior observed in a wide variety of in-reactor experiments.