Residual Plastic Deformation Research Articles

Effect of machining processes on the residual stress distribution heterogeneities and their consequences on the stress corrosion cracking resistance of AISI 316L SS in chloride medium

The effects of machining such as grinding and turning on the microstructural and mechanical changes of the machined surfaces of AISI 316L stainless steel (SS) have been studied. Surface aspects and surface defects have been examined by scanning electron microscopy (SEM). Machining-induced nanocrystallization has been investigated by transmission electron microscopy (TEM). Surface and subsurface residual stress distribution and plastic deformation induced by the machining processes have been assessed by X-ray diffraction (XRD) and micro-hardness measurements, respectively. The susceptibility to stress corrosion cracking (SCC) has been assessed by SEM examination of micro-crack networks which are characteristics of a machined surface immersed in boiling (140 ± 2 °C) solution of MgCl2 (40%) during a 48 h-period. The machined surface properties have been correlated to severe plastic deformation (SPD) resulting from specific cutting state of each process. High cutting temperature and plastic rate are considered to be at the origin of near-surface austenitic grain refinement that leads to equiaxed nanograins with a size ranging from 50 to 200 nm. Ground surface residual stress distribution heterogeneities at the micrometric scale are attributed to the random distribution of the density and the geometry of abrasive grains that represent micro-cutting tools in the grinding process. The relationship between residual stress distribution and susceptibility of the AISI 316L SS to SCC has been demonstrated, and an experimental criterion for crack initiation has been established.

Experimental Determination of the Static Equivalent Pressures of Detonative Explosions of Cyclohexane/O2/N2-Mixtures in Long and Short Pipes (part 1of 3)

Experimental Determination of the Static Equivalent Pressures of Detonative Explosions of Cyclohexane/O₂/N₂-Mixtures in Long and Short Pipes (part 1of 3)

Dynamic observation of X-ray Laue diffraction on single-crystal tungsten during pulsed heat load

The dynamics of the diffraction peak shape during pulsed heat load on mosaic single-crystal tungsten were measured at the `Plasma' scattering station on the eighth beamline of the VEPP-4 synchrotron radiation source at the Budker Institute of Nuclear Physics. The observed evolution of the diffraction peak shape agrees with theoretical predictions based on calculations of deformation caused by pulsed heating. Three clearly distinguishable stages of the diffraction-peak evolution were found, correlating with the evolution of temperature and deformation distributions. The residual plastic deformation increased with subsequent heating pulses.

Experimental and numerical investigation on the anti-penetration performance of metallic sandwich plates for marine applications

To predict the anti-penetration performance of protective structures, the ballistic performance of sandwich plates with steel face-sheet and aluminum foam core, the quasi-static compressive experiments of four different aluminum foam are performed and analyzed. The failure mechanism, mechanical parameters, and modified constitutive model are obtained. The virtual tests using numerical simulation were carried out in different penetration velocities based on quasi-static experimental constitutive parameters. Influence of projectile shape, face-sheet thickness, core thickness, and core densities on the residual velocity and plastic deformation of sandwich plates are discussed, while typical penetration failure modes and deformation mechanism are presented and analyzed. The failure modes of sandwich plates are different for hemisphere- and blunted-nosed projectile and the projectile shape influence is significant for ballistic performance when the penetration velocity approaches ballistic limit. The ballistic limit increases with increase of face-sheet or core thickness, core density and which shows an approximate linear relationship.

Finite element analysis of laser shock peening induced near-surface deformation in engineering metals

This paper investigates near-surface residual stress and equivalent plastic strain distributions using finite element method for further understanding of laser shock peening induced plastic deformation. The results indicate that residual stress and equivalent plastic strain at the topmost surface are sensitive to mesh size while they can be well predicted in the subsurface layer. Increasing laser spot size or overlapping rate deepens the compressive residual stress layer while reducing laser spot size leads to uniformly distributed residual stress and equivalent plastic strain. A minimum overlapping rate of 62.5% is necessary to create fully covered compressive residual stress on the target surface using round laser spot. Higher strain hardening exponent results in higher maximum compressive stress and equivalent plastic strain, deeper compressive residual stress and plastic deformation. In addition, higher elastic modulus results in lower equivalent plastic strain and shallower plastic deformation depth.

Microstructure, mechanical and thermal properties of Ni matrix composites reinforced with high-volume TiC

Composites with a high ceramic content (60 vol% TiC) and residual porosity below 1.9% were fabricated through liquid infiltration at 1515 °C under argon atmosphere. Scanning electron microscopy revealed a homogeneous distribution of the matrix phases and composite reinforcement, with slight superficial smoothing of the TiC particles due to a dissolution-precipitation process. System thermodynamics predict the partial dissolution of TiC particles and their precipitation during cooling, as well as the formation of insignificant quantities of Ti3O5 and Ti2O3 oxides. Nevertheless, only the phases corresponding to Ni and TiC were detected through x-ray diffraction. The microstructure, hardness values, modulus of elasticity, and flexural strength indicated strong adhesion between the ceramic and the metal. Good adhesion also favored the heat flow between the components, obtaining an effective thermal conductivity of 44–48.9 W/mK at a room temperature range of up to 700 °C. The incorporation of TiC particles lineally reduced the coefficient of thermal expansion (CTE) of the composite. Thermal cycling tests carried out from 25 to 450 °C showed that the composite exhibited an insignificant hysteresis cycle and a small residual plastic deformation, indicating high thermal stability. Thanks to its excellent dimensional stability, the composite is a potential candidate for applications in advanced engineering.

Effect of Underloads on Plasticity-Induced Crack Closure: A Numerical Analysis

The effect of underloads is mostly quantified by the averaged effect on the fatigue crack growth rate, and the transient behavior is rarely investigated. The objective of this paper is to study the mechanisms behind the effect of underloads, periodic underloads, and underloads combined with overloads. A single underload smashes the material around the crack tip, producing a depression on crack flank and a local reduction of contact forces at the minimum load. The reduction of plastic elongation behind the crack tip has an immediate effect on crack opening level, which rapidly disappears with crack propagation. The smashing associated with the compressive force occurs mainly behind the crack tip position where the underload was applied. The effect of the underload is intimately linked to reversed plastic deformation, which explains its enhanced effect for kinematic hardening. The decrease of load below the minimum baseline load is the main loading parameter. The application of periodic underloads extends the effect of a single underload. The effect of the underload is enhanced by the presence of obstacles in the form of residual plastic deformation, which explains the great effect of underloads applied after overloads.

Deformation and Residual Stress Measurement of Alumina Ceramics after Dynamic Impacts

Alumina ceramics sintered at 1350°C ~ 1550 °C with various mechanical properties were tested using a minitype compressed air gun with mini WC material bullets impacting at a fixed bullet speed of 100 m/s. The resistance behaviour and deformation were recorded by visual examination. Cr3+fluorescence was used to measure the induced residual stress and plastic deformation. The results show that the alumina with finest grains size and highest hardness is more effective in the bulletproof, the alumina sintered at 1450 °C experienced both the greatest extents of compressive residual stress (3.25 GPa) and plasticity (24 cm-1shift).

A Deep Learning-Based Computational Algorithm for Identifying Damage Load Condition: An Artificial Intelligence Inverse Problem Solution for Failure Analysis

In this work, we have developed a novel machine (deep) learning computational framework to determine and identify damage loading parameters (conditions) for structures and materials based on the permanent or residual plastic deformation distribution or damage state of the structure. We have shown that the developed machine learning algorithm can accurately and (practically) uniquely identify both prior static as well as impact loading conditions in an inverse manner, based on the residual plastic strain and plastic deformation as forensic signatures. The paper presents the detailed machine learning algorithm, data acquisition and learning processes, and validation/verification examples. This development may have significant impact on forensic material analysis and structure failure analysis, and it provides a powerful tool for material and structure forensic diagnosis, determination, and identification of damage loading conditions in accidental failure events, such as car crashes and infrastructure or building structure collapses.

Nonlinear dynamic behavior of simply-supported RC beams subjected to combined impact-blast loading

Despite many studies existed in the literature on the investigation of reinforced concrete (RC) structures under impact or blast loads separately, this paper numerically evaluates the nonlinear dynamic responses and failure behaviors of simply-supported reinforced concrete (RC) beams subjected to the combination of impact and blast loads using LS-DYNA. The effects of the middle-rate impact loading stresses on the blast responses of RC beams are studied by considering different combined loading scenarios varied by the sequence of applying loads and the time lag between the initiations of these loads. From the simulation results, it was observed that when the impact load is applied on the beam prior to blast loading, it suffers a more severe spallation in the depth due to the flexural-shear stresses generated in the impacted beam before the initiation of the subsequent blast load. In addition, the beam suffers a more severe spallation in the depth and residual plastic deformations when the subsequent blast load initiates during the free vibration stage of the beam subjected to impact load. However, larger peak values for the internal forces are generated when the subsequent blast load initiates simultaneously with the occurrence of the first peak of impact force. In addition, the vulnerability of different RC beams varied by some important structural parameters including the beam depth, the span length and the configuration of the reinforcements are assessed under a combination of impact and blast loads through a proposed damage index based on the residual flexural capacity of RC beams.

Research on the precision loss of ball screw with short-time overload impact

Ball screw is the driving functional component most frequently used for the precision equipment. To a certain extent, the transmission accuracy of precision equipment is affected by the position error of ball screw caused by the elastic–plastic deformation between ball and raceway under the overload impact. This article aims to investigate the precision loss of ball screw considering short-time overload impact. A novel precision loss model combining the Hertzian and Thornton contact theories is established to describe the variations in the axial deformation depths. Thus, the axial precision loss can be defined as the differential value between the initial no-loading travel variations and the loading stroke variations caused by the axial plastic deformation of raceway. Meanwhile, the maximum stress and the residual plastic deformation for four couples of ball-raceway materials are analyzed. Furthermore, the relationship between the precision loss and the elastic–plastic deformation is studied by the theoretical analysis and experiments. The results show that the position and precision is affected indeed by the contact deformation. The position and precision loss of the nut relative to the screw increases with the increase in the axial load. The results can help to provide the prediction for the precision life of ball screw operating in high-load condition.

Експлуатаційні дослідження показників кутового зсуву клейової полімерної пластини корінцевої частини книжкового блоку

The purpose of the work is to study the deformation of the adhesive layer of the root portion of the book block, stitched threads, the influence of the bending angles of the polymeric adhesive plate during the exploitation of book products, which contribute to the creation of zones of variable concentration of destructive stresses of the internal structure of the plate, as well as the influence of the time of the load on these areas, that proportionally influence on the reduction of the elastic properties of the plate and the development of residual plastic deformation phenomena. The amount of deformation of individual sections of a radial adhesive polymer plate, during operational loads when using book blocks stitched together, depends not only on the elastic material properties of the adhesive composition, its isotropy, the thickness of the applied layer, but also on the angles of the plate kinks that contribute to creating variable zones concentration of destructive stresses of the internal structure. Stresses occur at the edges of the joints of the glue plate with the paper of the folds of the backs of the notebooks on the one hand, and the edging paper, on the other hand, in the form of sections of compression and tension in places of discrete kinks. The duration of the loads in these areas, in proportion to the decrease in the elastic properties of the plate and the increase in the phenomena of residual deformation. Taking into account the negative influence of discrete angular bends of rooted glue polymeric plates in any part of it and the heterogeneity of the duration of loads during the exploitation of book products lead to deformation formed during bending of the plate and promotes the accelerated transformation of processes of elastic deformation into residual processes of plastic deformation. The use of high strength and high elastic adhesive compositions, which do not have a negative effect on the stiffness and bending stability of the glued system, can minimize the disadvantages of the angular displacement, which in turn will provide a prolonged operating period and a favorable competitive appearance of book products.

Numerical analysis of hydrogen transport into a steel after shot peening

Abstract Surface peening is a potential method of suppressing hydrogen embrittlement (HE). But experimental observations in literatures have shown that it can suppress HE of steels exposed to a mild hydrogen-containing environment, but in a severe hydrogen-containing environment it enhances HE. To explain this from the perspective of hydrogen transport and concentration, this paper gives a numerical analysis of hydrogen transport into a PSB1080 high strength steel after shot peening (SP) focusing on the combined effect of residual compressive stress and SP plastic deformation on diffusion. The diffusion model established by Oriani and Sofronis et al. is used, which considers the effect of the increase of trap sites due to plastic strain and assumes that the populations of hydrogen in trap sites and in normal lattice sites are in equilibrium. The results were related to experimental observations. In mild hydrogen-containing environment, the increase of trap sites due to SP can significantly reduce the apparent hydrogen diffusivity, thus suppress the transport and resulting hydrogen concentration level in normal lattice sites. As a result, hydrogen trapped at grain boundaries is reduced, and HE mechanism changes from HEDE to simultaneous HELP and HEDE. Intergranular fracture is suppressed thus reducing HE. And the suppression of hydrogen transport increases with increasing shot velocity, as a faster shot gives rise to more severe plastic deformation. In severe hydrogen-containing environment, SP deformation has little influence on diffusivity but significantly increases trapped hydrogen, leading to irreversible hydrogen blisters hence enhancing HE.

Кількісний аналіз орієнтації та видовженості зерен на металографічних зображеннях за допомогою перетворень Хафа

Однією з форм представлення результатів неруйнівного контролю різноманітних металоконструкцій є металографічні зображення. Це зображення мікроструктури металу, які формуються за допомогою мікроскопа і фотофіксувального пристрою. З погляду матеріалознавства, мікроструктура відображає внутрішню будову металу та складається із різноманітних об'єктів – зерен, меж зерен, карбідів, різноманітних включень тощо, які характеризуються розміром, формою, орієнтацією. Мікроструктура матеріалу є віддзеркаленням його фізико-механічних характеристик. Отже, актуальною є задача аналізу мікроструктури матеріалів, яка надасть нові можливості щодо кількісного оцінювання їх фізико-механічних властивостей. Візуальний аналіз не забезпечує потрібної швидкодії та точності опрацювання, тому для вирішення задачі аналізу мікроструктури найдоцільніше використовувати методи оброблення цифрових зображень. Залежно від поставленої мети, задача аналізу мікроструктури полягатиме у пошуку та обчисленні метричних розмірів складників мікроструктури, оцінюванні їх форми, формуванні певної статистики тощо. У цій роботі розроблено метод кількісного аналізу орієнтації та видовженості зерен на металографічних зображеннях за допомогою перетворення Хафа. Результати цього аналізу є основою для досліджень залишкових напружень та пластичних деформацій металів.

Residual Stresses and Plastic Deformation in Self-Pierce Riveting of Dissimilar Aluminum-to-Magnesium Alloys

Residual Stresses and Plastic Deformation in Self-Pierce Riveting of Dissimilar Aluminum-to-Magnesium Alloys

Dynamic finite element analysis of shot peening process of 2618-T61 aluminium alloy

Shot peening is one of the surface treatment processes usually used for the improvement of fatigue strength of metallic parts by inducing residual stress field in them. The evaluation of shot peening parameters experimentally is not only very complex but costly as well. An attractive alternative is the explicit dynamics finite element (FE) analysis having the capability of accurately envisaging the shot peening process parameters using a suitable material’s constitutive model and numerical technique. In this study, ANSYS/LS-DYNA software was used to simulate the impact of steel shots of various sizes on 2618-T61 aluminium alloy plate described with strain rate dependent elasto-plastic material model. The impacts were carried out at various incident velocities. The effect of shot velocity and size on the induced compressive residual stress and plastic deformation were investigated. The results demonstrated that increasing the shot velocity and size yielded in an increase in plastic deformation of the aluminium target. However, as observed, the effect of shot velocity and size was small in magnitude on the target's subsurface compressive residual stress.

К вопросу о реконструкции остаточных напряжений и деформаций пластины после дробеструйной обработки

Предметом исследования является математическое описание формы и напряженно-деформированного состояния стальной пластины, подвергнутой односторонней дробеструйной обработке, его экспериментальное подтверждение и применение результатов для верификации методов реконструкции полей остаточных напряжений и деформаций по экспериментальным данным. Подобная пластина используются на производстве в качестве калибровочного образца для определения времени пневмодробеструйной обработки, необходимого для формирования в поверхностном слое обрабатываемого изделия сжимающих тангенциальных остаточных напряжений заданной величины, а сам метод калибровки оказывается удобным и довольно широко распространенным для различных способов поверхностно упрочняющей обработки. Источником остаточных напряжений в данном случае является пограничный слой пластических деформаций, наводимый рассматриваемым технологическим процессом. Для постановки задачи задается структура поля тензора пластических деформаций. Форма и напряженно-деформированное состояние упругой пластины с пограничным слоем пластических деформаций были рассчитаны численно, в результате чего были выявлены качественные особенности данных полей, ослаблены граничные условия задачи и сформулированы гипотезы о структуре решения соответствующей пространственной задачи теории упругости, которое далее было найдено аналитически. Показано, что в рамках приближения плоского напряженного состояния в поперечных направлениях результат точно соответствует формуле Давиденкова - Биргера, связывающей зависимость тангенциальной компоненты остаточных напряжений от координаты по толщине пластины с функцией прогибов. Получена явная формула для зависимости остаточной (пластической) деформации от координаты по толщине. Проанализированы источники погрешностей полученных выражений и способы их коррекции. Проведен эксперимент по односторонней дробеструйной обработке калибровочной пластины, изготовленной из закаленной стали 65Г, для которой выполнено травление обработанной поверхности с измерением изменения стрелы прогиба (метод Н. Н. Давиденкова). С помощью полученных экспериментальных данных были численно реконструированы профили остаточных напряжений и деформаций с разумной точностью. Результат применим к широкому классу задач для упругих тел с упрочняющими покрытиями, а также имеет определенную методическую ценность для усовершенствования основ экспериментального исследования таких задач, позволяет формулировать и подтверждать экспериментом гипотезы о структуре решения, изучать связь рассматриваемых полей в предельных случаях, верифицировать применение различных способов учета остаточных напряжений и деформаций в численных расчетах. Найденное решение может быть использовано для верификации полей напряжений и перемещений при выборе различных вариантов предварительно напряженных или деформированных поверхностных оболочечных конечных элементов в рамках пакетов прикладных программ для расчета усталостной долговечности деталей машин с поверхностными упрочняющими покрытиями и также представляется опорным для исследования поверхностно упрочненных тел с криволинейной свободной границей, к которым сводится большинство практически важных задач.

Comparison of the stress-strain state of the reinforced concrete structure under various mathematical models of concrete

Nowadays, reinforced concrete structures are most often used as load-bearing elements of buildings and structures. In the case of alternating loads such as seismic action, there is accumulation of residual plastic deformations in the concrete structures, which leads to a significant complication in the calculation of structures by “standard” methods. For such problems, it is advisable to use computational complexes in which mathematical models of structural materials are implemented, which allow to describe the work of concrete and reinforcing bars for various types of impacts more properly. However, when applying such methods, the results obtained should not contradict the requirements of the existing regulatory documents, which, in the first place, the structural engineer should be guided by. Before solving more complex problems, the applied methods should be verified and analyzed for fairly simple structures and types of loads.

Semi-analytical models for flexure deformation in one-step simulation of sheet metal forming

This paper presents the application of multi scale techniques to the simulation of sheet metal forming using the one-step method. When a blank flows over the die radius, it undergoes a complex cycle of bending and unbending. First, we describe an original model for the prediction of residual plastic deformation and stresses in the blank section. This model, working on a scale about one hundred times smaller than the element size, has been implemented in SIMEX, one-step sheet metal forming simulation code. The utilisation of this multi-scale modeling technique improves greatly the accuracy of the solution. Finally, we discuss the implications of this analysis on the prediction of springback in metal forming.

Simultaneous evaluation of residual stress and plastic deformation in ferromagnetic steel by using an integrated NDE method

Simultaneous evaluation of residual stress and plastic deformation in ferromagnetic steel by using an integrated NDE method