Residual Plastic Research Articles

Accelerated weathering of textile waste nonwovens used as sustainable agricultural mulching

The removal of agriculture residual plastic films is nowadays a big concern for all environmentalists. Several ecological alternatives were developed for more sustainable products and cleaner production. In this work, the effect of three months of exposure under accelerated weathering conditions (ultraviolet light, moisture, and heat) on the properties of two textile waste nonwovens as a sustainable alternative to plastic mulching films was investigated. Results showed that thermostability and mechanical properties of the clothing textile waste felt and cotton waste nonwoven decreased after accelerated weathering. The chemical variation of cotton waste nonwoven and textile waste felt and the degradation rate of natural and synthetic fibers due to the photolysis and hydrolysis caused by accelerated weathering conditions were studied following the Fourier transform infrared spectroscopy and the fibrous composition variation of the blended textile waste felt structure during the study.

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.

Investigation on the effect of shot peening coverage on the surface integrity

Shot peening is a typical surface strengthening process that is widely applied in engineering practice for it can introduce finer grains in the near-surface layer and generate a compressive residual stress (CRS) layer. The finite element method, together with a Python subscript, is applied to create a multiple-shot model to estimate the evolution of the shot peening coverage. The influences of coverage on residual stress, plastic strain and surface topography are discussed. The predicted results reveal that as the shot peening coverage increases from 100% to 400% under the given processing condition, the maximum CRS and the plastic strain will increase gradually. But there is no evident alteration on the width of CRS layer and plastic strain layer. The variations of each roughness parameter with coverage are different.

Stability analysis of strain-softening slopes based on the gravity increase method

With traditional slope stability analysis methods, it is difficult to accurately describe the progressive failure process and dynamic variation law of slope stability. The strain-softening constitutive model was therefore used to simulate the progressive failure process of a strain-softening slope based on the gravity increase method (GIM), with the displacement interface employed to determine the sliding surface. A sensitive analysis of the characteristic parameters within the softening stage was then conducted. The results are as follows: There are similar space-time evolution laws of residual strength factor and shear strain increment, with failure starting from the slope toe and extending gradually. The sliding surface of strain-softening slopes is located between that of the slope with peak strength and the sliding surface of the slope with residual strength. The stability coefficient shows an exponential growth trend with the increase of residual cohesion and residual plastic shear strain threshold, with a positive linear correlation between the residual friction angle and stability factor. The residual friction angle is the most sensitive factor in slope stability, followed by the residualcohesion, with the residual plastic shear strain threshold being the least sensitive.

Damage evolution in high density polyethylene under tensile, compressive, creep and fatigue loading conditions

Influence of various loading histories on mechanical properties and damage evolution of polyethylene (PE) is quantified through a two-stage test method. The first-stage tests are to introduce damage by subjecting the specimens to different prestrain levels under tensile, compressive, creep and fatigue loading condition. Two months later, the second-stage tests apply monotonic tensile loading at a crosshead speed of 0.01 mm/min to characterize the mechanical properties for specimens that have had damage generated in the first-stage tests. Experimental results suggest that yield stress and loading stiffness decrease and residual plastic strain increases with the increase of prestrain introduced in the first-stage tests. Damage evolution law, based on the degradation of loading stiffness has been established as a function of prestrain and residual plastic strain. Results show that damage variable expressed as a function of prestrain strongly depends on loading conditions applied in the first-stage tests. However, damage evolution described by the relationship between damage variable and plastic strain is found to be independent on the loading condition, suggesting that a unified, plastic strain controlled damage evolution law can be established for PE materials.

On the influence of overloads on the fatigue performance of deep rolled steel SAE 1045

The present paper analyzes the influence of overloads on the fatigue strength and residual stress stability for a tempered and deep rolled steel SAE 1045. Deep rolling has been conducted at room temperature and 250 °C. A single overload as well as blocks of 10 and 100 overloads were applied at two different overload levels of 25% and 50%. A single baseline amplitude of 800 MPa at a stress ratio of R = −1 was considered for fatigue testing. It is shown that overloads negatively influence the near surface areas resulting in significant reduction of the fatigue life up to about 75%. The consequences of overloads on residual stress stability and plastic strain behavior were assessed in depth. Findings presented clearly reveal that residual stress relaxation as well as an increase of plastic strain upon overloading are affected by both the absolute value and the number of overload cycles. Furthermore, conditions deep rolled at elevated temperature, showing superior performance under constant amplitude loading, most severely suffer from overloads.

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.

Oral levodopa rescues retinal morphology and visual function in a murine model of human albinism.

Albinism is a group of disorders characterized by pigment deficiency and abnormal retinal development. Despite being a common cause for visual impairment worldwide, there is a paucity of treatments and patients typically suffer lifelong visual disability. Residual plasticity of the developing retina in young children with albinism has been demonstrated, suggesting a post‐natal window for therapeutic rescue. L‐3, 4 dihydroxyphenylalanine (L‐DOPA), a key signalling molecule which is essential for normal retinal development, is known to be deficient in albinism. In this study, we demonstrate for the first time that post‐natal L‐DOPA supplementation can rescue retinal development, morphology and visual function in a murine model of human albinism, but only if administered from birth or 15 days post‐natal age.

Strength and cohesive behavior of thermoset polymers at the microscale: A size-effect study

This study investigated, experimentally and numerically, the fracturing behavior of thermoset polymer structures featuring cracks and sharp u-notches. It is shown that, even for cases in which the sharpness of the notch would suggest otherwise, the failure behavior of cracked and pre-notched specimens is substantially different, the failure loads of the former configuration being about three times lower than the latter one. To capture this interesting behavior a two-scale cohesive model is proposed. The model is in excellent agreement with the experimental data and its predictions allow to conclude that (a) residual plastic stresses cannot explain the very high failure loads of notched structures; (b) the strength of the polymer at the microscale can be from six to ten times larger than the values measured from conventional tests whereas the fracture energy at the microscale can be about forty times lower; (c) the pre-notched specimens investigated in this work failed when the stress at the tip reached the microscale strength whereas the cracked specimens failed when the energy release rate reached the total fracture energy of the material. The foregoing considerations are of utmost importance for the design of microelectronic devices or polymer matrix composites for which the main damage mechanisms are governed by the strength and cohesive behavior at the microscale.

Influence of residual plastic strain on the thermoelastic behavior of a titanium alloy

The thermoelastic effect that manifests as a change in temperature of a body undergoing adiabatic elastic deformation has been utilized for full-field stress analysis in solids using the infrared thermal imaging technique. This technique has been used for nondestructive evaluation of residual stresses in components. The present study endeavors to examine the effect of residual plastic strain, due to a previously imposed plastic deformation, on the thermoelastic behavior of solids. Near-α titanium alloy specimens have been plastically deformed, and after reaching a plastic strain level, the test has been interrupted. The thermoelastic response of the interrupted specimens has been examined. The infrared thermal imaging technique has been used to capture the spatiotemporal evolution of the surface temperature of the specimens. It has been observed that the thermoelastic coefficient of the alloy increases as a function of prior/residual plastic strain for small deformations. It has been shown that the theoretical framework used to explain the effect of residual stress on the thermoelastic coefficient assuming a perfect crystal lattice is not applicable to explain the effect of residual plastic strain on the thermoelastic coefficient. A modification of the existing theory has been proposed to explain the dependence of the thermoelastic coefficient on the residual plastic strain. A thermodynamic framework considering the local entropy and internal energy density has been developed to study the behavior. The microscopic aspects of the energetic of thermoelasticity have been discussed and based on this a continuum dislocation dynamic model has been proposed to explain the variation in the thermoelastic coefficient.

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.

Fatigue crack growth in notched specimens: a numerical analysis

Fatigue crack growth (FCG) is linked to irreversible and non-linear processes happening at the crack tip, which explains different problems observed in the use of da/dN-DK curves. The replacement of DK by non-linear crack tip parameters, namely the crack tip opening displacement (CTOD) is an interesting alternative. The objective in here is to study the effect of notches on FCG using the plastic CTOD range, dp. M(T) specimens with lateral notches of different radius (1, 2 4 and 8 mm were analysed numerically, keeping the total depth constant (8 mm). The increase of crack length increases dp and therefore FCG rate. For plane stress state, the formation of the residual plastic wake with crack propagation produces crack closure which compensates the effect of crack length and there is a stabilization of dp. The reduction of notch radius increases dp for all crack lengths, particularly for the shortest ones. For plane strain state there is almost no crack closure therefore dp is higher than for plane stress state, and the effect of crack length produces a relatively fast increase of dp

Edge Effect Investigation of DP980 Steel Sheet in Multiple Laser Scanning Process

Due to free spring back, laser forming is an effective non-contact forming technique for hard forming materials. A desired shape is obtained by residual plastic strain which is induced by thermal stresses depending on multiple laser scanning. In this study, the combination of experimental and numerical analysis is employed to investigate the temperature distribution and bending angle of the dual phase (DP980) high strength steel sheet. The edge effect of six cases of laser scanning process involving 1, 2, 3, 4, 5 and 10-time laser scanning are investigated by analyzing their bending angle relative variations and transverse plastic strains. It is found that the edge effect at the middle part of laser scanning line reduces with the increasing number of laser scanning cycles. It is attributed to the fact that the relative variation of the residual plastic strain reduces with the increase of laser scanning cycles. To efficiently reduce the edge effect of DP980 steel sheet, a locally repeated scanning strategy is proposed. The numerical simulation results indicate that the edge effect reduces significantly in the 10-time laser scanning process and the average bending angle simultaneously increases around 20% under the new laser scanning strategy.

Formation mechanism of abnormally large grains in a polycrystalline nickel-based superalloy during heat treatment processing

Controlling the final grain size in a uniform manner in powder metallurgy nickel-based superalloys is important since a number of mechanical properties are closely related to it. However, it has been widely documented that powder metallurgy superalloys are prone to suffer from growth of abnormally large grains (ALGs) during supersolvus heat treatment, which is harmful to in-service mechanical performance. The underlying mechanisms behind the formation of ALGs are not yet fully understood. In this research, ALGs were intentionally created using spherical indentation applied to a polycrystalline nickel-based superalloy at room temperature, establishing a deformation gradient underneath the indentation impression, which was quantitatively determined using finite element modeling and synchrotron diffraction. Subsequent supersolvus heat treatment leads to the formation of ALGs in a narrow strain range, which also coincides with the contour of residual plastic strain in a range of about 2%–10%. The formation mechanisms can be attributed to: (1) nucleation sites available for recrystallization are limited, (2) gradient distribution of stored energy across grain boundary. The proposed mechanisms were validated by the phase-field simulation. This research provides a deeper insight in understanding the formation of ALGs in polycrystalline nickel-based superalloy components during heat treatment, when subsurface plastic deformation caused by (mis)handling occurs or small residual strain has been retained from hot/cold working before supersolvus heat treatment.

Effect of loading sequences on fatigue crack growth and crack closure in API X65 steel

This paper presents a predictive model for fatigue crack growth under loading sequences. Several parameters had been quantified mainly under variable amplitude loading due to its peculiarities. The applicability of the crack closure model was studied to predict the fatigue life span resulting from the continuous effect of loading blocks. The API grade X65 steel, which is widely used in the crude oil and gas industries, was used in this study. Spectrum loading with a two-level block sequences, designated as high-to-low and low-to-high, were designed to correspond to variable amplitude loading. A stress ratio of 0.1 and 0.7 was retained at each block sequences. The effect of block transition from high-to-low caused a delay in crack growth due to the residual plastic wake left behind the crack tip. The crack growth under low-to-high loading blocks were faster than that under high-to-low loading blocks. A modified Walker was established and demonstrated to be capable of describing the features of crack arrest and crack growth acceleration under continuous loading sequences. The normalised root-mean-square error of the predictive model ranged from 0.05 to 0.22 at both load ratios. The integrated crack closure into Walker can reasonably predict the influence of loading sequences on the fatigue crack growth in the API X65 steel.

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).

МАТЕМАТИЧЕСКОЕ МОДЕЛИРОВАНИЕ НАПРЯЖЕННО-ДЕФОРМИРОВАННОГО СОСТОЯНИЯ В ПОВЕРХНОСТНО УПРОЧНЕННЫХ ВТУЛКАХ С УЧЕТОМ ОСТАТОЧНЫХ КАСАТЕЛЬНЫХ НАПРЯЖЕНИЙ

We suggest the phenomenological mathematical model of the stress-strain state reconstruction in the surface hardened thin-walled tube with an inner diameter 45 mm and outer diameter 51.5 mm made of steel EI961 and treated by diamond smoothing of the outer surface. It is shown that if all stress components depend on radius only, then the components are in the cylindrical coordinate system. The experimental research is made for the samples which were softened under two load modes (radial force) of the diamond ball attachment of 200 and 300 N value. The experimental values of residual stresses , , and in the surface layer are obtained by the ring and strip method using the layer-by-layer electrochemical pickling of the hardened layer. The experimentally measured values of the strip beam deflection, split ring angular opening and axial displacement of cut edges relative to each other are used for this purpose. The hardening anisotropy parameter which relates the axial and circumferential components of plastic strain is included in the mathematical model. To solve the formulated problems we use the hypotheses of plastic incompressibility of the material, the absence of secondary plastic deformations of the material in the surface layer compression area and the hypotheses of flat sections and straight radii. We present the method for solving the stress-strain state reconstruction boundary value problems, which allows obtaining the missing component and all residual plastic strain components. The validation of the computational data obtained by mathematical modelling for adequacy to the experimental data for the two modes of hardening is made. There is a close agreement between the computational and experimental data. The numerical values for the hardening anisotropy parameter are given. By using this parameter we are able to theoretically describe the observable experimental layering of axial and circumferential stresses in depth of the hardened layer. It is theoretically and experimentally established that the absolute values of maximum shear stresses is an order of magnitude smaller than the absolute values of maximum normal stresses. We also discuss the questions of the effect of shear stresses on high-cycle fatigue and creep of the hardened thin-walled tubes. The main results of the research are illustrated by the tabular data and corresponding diagrams of the residual stresses distribution in depth of the hardened layer.

Деформовність маловуглецевого дроту в процесі його багатоступінчастого холодного волочіння

The aim of the work is to analyze the distribution of deformations over the cross section, features of the deformation paths, also is carried out the assessment of wire deformability from low carbon steels typical for the modern market G3Si1 and Sv-08G2S during its multistage cold drawing. For the analysis, one of the typical technological processes of drawing with 16 transitions was selected, which is aimed at the production of wire with a diameter of 0.8 mm from a rod of diameter 5,5 mm. This process is implemented in real production in the PJSC «PlasmaTek» environment. The mechanics of cold drawing process are carried out using the finite element method. The evaluation of deformability was performed using the V. Ogorodnikov criterion, which takes into account the nonlinear nature of damage accumulation, the features of deformation paths in the form of derivatives, as well as the stress state indicator, taking into account the third invariant of the stress tensor (volume of the stress state). The analysis of the distribution of deformations in the section through their representation in relative units carried out. It is shown that the graphs of the distribution of strains over the cross section practically coincide for different transitions and diameters of the workpieces. The coefficient of non-uniformity of deformations practically does not depend on the number of transitions and the degree of stretching and reaches 0, 87. The deformation paths in the hazardous area — on the axis of the wire — are analyzed — they are characterized by a significant change in the derivative and curvature of the deformation territory. It is established that the indicators of the stress state, taking into account the volume of the stress state (in particular, the parameter Nadai–Lode) practically do not change during cold drawing. Сonsidering at third invariant of the stress tensor with the appropriate deformability criterion makes it possible to correctly evaluate the deformability of low-carbon welding wire in its drawing process in existing drawing practices and to further implement on this basis the assessment of technological heredity in the form of residual plasticity, hardness, and ect.

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.