Induce Plastic Deformation Research Articles

Microscopic Failure Mechanism of Zinc Layer in Galvanized Sheet during Sheet Forming Process

Sheet forming of galvanized metals presents a great challenge for automobile industry. This is partially caused by a significant induced plastic deformation and high contact friction during forming, which results in pulverization, flaking and failure seen in the zinc layer. Cupping tests is used to study the formability of the galvanized sheets, for a better understanding of microscopic failure mechanisms of the zinc layer. The results show that during the cupping of the galvanized sheet, the zinc layers of each deformed zone encounter varying degrees of failure behaviors. The regions next to the fillets of the punch and the blank holder ring are more serious. In these severe failure areas, the residual stresses in the zinc layer are shown as tensile in nature; and increase with the degree of deformation increasing. The galvanized layers rupture prematurely prior to any damage seen in the steel substrate; thus leading to chalking, flaking and final failure. The results provide a theoretical guidance for improving formability of galvanized sheets.

Plastic deformation and grain refinement in surface layer induced by thermo-mechanical loads for hard milling process

Microstructure alteration of machined surface induced by the coupled thermal and mechanical loads in the hard milling process has great influence on surface integrity. Hence, it affects the performances of the workpiece. The hard milling experiments of AISI H13 steel with different cutting speeds and feed rates were carried out and the microstructure evolution of machined surface was investigated by means of some advanced characterization methods. The experimental result indicates that plastically deformed layer was evident with three distinguishable zones, that is, unaffected zone, plastic deformation zone, and white layer zone. X-ray diffraction analysis revealed that no retained austenite is detected in the white layer. Numerous nano-sized equiaxed grains were induced by dynamic recrystallization (DRX), as a result of severe shear plastic deformation on the machined surface. As the cutting speed increases, the grain refinement becomes more obvious. However, the original cementite was greatly refined and well distributed compared with bulk material. A significant improvement in nano-hardness was witnessed in both for machined surface and subsurface. The grain refinement as well as well-dispersed cementite played a vital role in the improvement of nano-hardness. The varied depth of plastic deformation was observed with respect to change of cutting forces. It is the main source of mechanical load inducing plastic deformation with the assistance of material thermal softening. The present work can provide more visibility on the surface integrity along with the quality control of the workpiece.

Strengthening mechanisms in directed energy deposited austenitic stainless steel

Microstructures and mechanical properties are evaluated in austenitic stainless steel structures fabricated by directed energy deposition (DED) considering the effects of applied loading orientation, build geometry, and distance from the deposition baseplate. Locations within an as-deposited build with different thermomechanical history display different yield strength, while those locations with similar history have approximately the same yield strength, regardless of test specimen orientation. Thermal expansion of deposited material near the baseplate is inhibited by the mechanical constraint imposed by the baseplate, promoting plastic deformation and producing a high density of dislocations. Concurrently, high initial cooling rates decrease away from the baseplate as the build is heated, causing an increased spacing of cellular solidification features. An analysis of strengthening mechanisms quantitatively established for the first time the important strengthening contribution of high dislocation densities in the materials (166–191 MPa) to yield strength that ranged from 438 to 553 MPa in the present DED fabricated structures. A newly adopted mechanistic relationship for microsegregation strengthening from the literature indicated an additional important contribution to strengthening (123–135 MPa) due to the cellular solidification features. These findings are corroborated by the measured evolution of microstructure and hardness caused by annealing the DED material. These results suggest that the mechanical properties of deposited austenitic stainless steels can be influenced by controlling thermomechanical history during the manufacturing process to alter the character of compositional microsegregation and the amount of induced plastic deformation.

N2supercritical jet to modify the characteristics of polymer material surfaces: Influence of the process parameters on the surface topography

Foreign body reaction (FBR) is a critical issue to be addressed when polymeric implants are considered in the medical field to treat pathologies involving hernia repair, revascularization strategies in arterial disease, and aneurysm or heart valve replacement. The natural porosity of textile materials tend to induce exaggerated tissue ingrowth which may prevent the implants from remaining flexible. One hypothesized way to limit the FBR process is to increase the material surface roughness. Supercritical N2jet particle projection is a novel technique to provide enough velocity to particles to induce plastic deformation on the impacted surface. This work investigates the influence of supercritical N2jet projection parameters like jet static pressure, standoff distance (SoD), particle size and density on the roughness that can be obtained on polyester flat polymer surfaces. Results bring out that particles generate craters on the polymeric impacted surface, with size increases correlated with the jet pressure and the particle diameter. With a pressure of 1,000 bars, 300‐mm SoD, and a particle mass flowrate of 0.6 g/s, it is possible to obtain a uniform 5 μm roughness on the impacted surface. This value is in the range of the 10 μm fiber size which is commonly used in medical textile implants. Basically, result brings out that whatever the particle size or particle flow rate, the SoD has the most significant effect on the roughness. POLYM. ENG. SCI., 59:616–624, 2019. © 2018 Society of Plastics Engineers

Influence of Work‐Hardening and Lower Temperatures on the Yield Stress of Austenitic Stainless Steel X2CrNi18‐10 under Combined Tension‐Torsion Loading

This study investigates the impact of work‐hardening and lower temperatures on the mechanical properties of austenitic stainless steel X2CrNi18‐10 under multiaxial stress. For this purpose, the yield behavior of hollow tubular specimens under combined torsion‐tension loading is examined using a servo‐hydraulic testing system MTS809.10S. Yield points are determined for different tension‐to‐torsion ratios using 1) solution‐annealed specimens tested at room temperature, 2) pre‐strained specimens with 3.6% α’‐martensite tested at room temperature, and 3) solution‐annealed specimens tested at −20 °C. Experimental results show that the yield stresses of the solution‐annealed material at room temperature and at −20 °C can be reasonably approximated using the von Mises and the isotropic Hosford yield hypothesis. Contrary, the yield stresses of the work‐hardened material cannot be fitted with isotropic yield hypotheses because the required torsional stress component to induce plastic deformation is much higher than suggested in those criteria. This effect is mainly attributed to the strain hardening behavior of the X2CrNi18‐10, showing a comparatively high rate of work‐hardening especially at low strains. A suitable approach for fitting the yield points of the work‐hardened material is found with the anisotropic yield hypothesis according to Hosford.

Cavitation-crazing transition in rubber toughening of poly(lactic acid)-cellulose nanocrystal composites

In this work, the mechanism behind rubber toughening of poly(lactic acid)/cellulose nanocrystal-g-rubber-g-poly(d-lactide) (CNC-rDx-PDLA) composites was elucidated through systematic study of the effects of rubber segment content (length) in CNC-rDx-PDLA nanofillers and the nanofiller concentrations on the deformation behavior of the nanocomposites. It was shown that with an increase of rubber segment length and rubber filler concentration, the elongation at break of the resulting composites increased. Moreover, a dramatic increase in elongation at break (from 20% to 200%) was observed when the rubber segment content (length) in the CNC-rDx-PDLA nanofillers was increased from 52 to 68%. Cavitation mechanism was found dominant when the rubber segment content in the nanofillers was 52% and below, whereas, stable crazes were formed and followed by fibrillation when the rubber segment content in the nanofillers was increased to 68%, which was evident by small angle X-ray scattering (SAXS) study and scanning electron microscopy (SEM) analysis. The existence of a transition from cavitation to crazing in the composite systems could be attributed to a more mobile rubber phase because of longer rubber chain length. Our study suggests that the effective toughening mechanism for thermoplastics such as PLA is crazing induced plastic deformation.

Electromagnetic Levitation Control for Bending Flexible Steel Plate: Experimental Consideration on Disturbance Cancellation Control

When an ultrathin and flexible steel plate is to be levitated, levitation control becomes difficult because the ultrathin steel plate undergoes increased flexure. We herein propose a levitation method for an ultrathin steel plate that is bent to an extent that does not induce plastic deformation. In this study, to investigate the levitation stability of an ultrathin steel plate, we applied disturbance cancellation control in the bending levitation system. The object of electromagnetic levitation was a rectangular zinc-coated ultrathin steel plate (SS400) of length 800 mm, 600 mm, and thickness 0.19 mm. The vibrator was attached below the three frames, in which the electromagnet unit was installed so that the frames could be vibrated up and down. We conducted experiments on the levitation performance when the electromagnet was displaced by the frame vibration in the bending levitation system. The results showed that a stable levitation can be achieved even with an input of external disturbance when levitating at the optimum bending angle.

Consequences of a Room-Temperature Plastic Deformation During Processing on Creep Durability of a Ni-Based SX Superalloy

Ni-based single crystalline superalloys are used for high-pressure parts of aero-engines due to their superior mechanical properties and very good oxidation resistance at high temperature. However, shocks or unexpected mismatch in thermal contraction between molds and castings can occur during casting process and subsequent heat treatments, inducing plastic deformation of the alloy at low temperature. To mimic such events, a tensile plastic deformation is applied at room temperature on solutioned AM1 specimens and followed by standard aging heat treatments. Faster growth of the γ′ precipitates inside plastically deformed bands is obtained after full heat treatment with no lattice rotation or recrystallization. It has however been evidenced that the applied deformation has a detrimental impact on the creep properties, especially at high temperature (above 950 °C). It partly results from a highly localized failure process along former slip bands in which recrystallization is observed. The evolution of the microstructure during creep tests of prior deformed and nondeformed specimens has been thoroughly investigated to better identify under which conditions recrystallization occurs inside the bands during a creep test and by which mechanism.

A 3D efficient finite element model to simulate rolling contact fatigue under high loading conditions

Abstract The objectives of this investigation were to develop a 3D efficient elastic-plastic finite element model to characterize the rolling contact fatigue behavior of through hardened steel at high loads (∼5 GPa) and to corroborate analytical and experimental results. The efficient FE model developed for this investigation was coupled with the continuum damage mechanics to simulate rolling contact fatigue (RCF). The new computationally efficient approach developed uses Delaunay mesh to reduce the number of elements without compromising the accuracy of stress distribution induced during a rolling contact pass. In order to validate the newly developed approach, the results obtained from the current 3D model for line contact were corroborated to previously published results. The fatigue lives obtained from the new model are consistent with the previously published model predictions and empirical observations. In order to simulate the RCF for high load conditions, the increase in the contact width observed in the experiments and consequently the decrease in the contact pressure with loading cycles were implemented in the model. Furthermore, the damage evolution law was modified to incorporate the compressive residual stresses induced by the plastic deformation. The L10 life and the scatter in the fatigue lives obtained from the model correlated well with the experimental results. As a part of this investigation, a Thrust Bearing Test Apparatus (TBTA) was designed and developed to simulate RCF. RCF experiments were conducted on through hardened AISI 52100 steel flat specimens at high contact stress levels (5 GPa) to induce plastic deformation. The results demonstrated that the contact width increased as the cycles increased due to plastic strain accumulation. The results from FE model corroborate well with experimental results obtained from TBTA.

Alternative method for the identification of the strain hardening behaviour along the rolling direction of coil

AbstractA new method is proposed for the measurement of the mechanical properties of X70 coil steel along the rolling direction using an inverse procedure and digital image correlation. To characterise the mechanical properties, a tensile test was performed on a curved API sample. To clamp the curved sample without inducing plastic deformation, additional shims were machined compensating the curved clamping region. Using this modified test setup, finite element model updating, and digital image correlation, the mechanical properties were identified without influencing the material behaviour and considering the entire wall thickness. These results were compared with a flattened API tensile specimen. A yield stress reduction was found compared with the identified yield stress on the curved specimen equipped with shims. Additionally, the influence of the residual deflection after flattening on the yield stress has been scrutinised.

Influence of different shot peening treatments on surface state and fatigue behaviour of Al 6063 alloy

Shot peening is a surface treatment commonly used to improve the fatigue behaviour of mechanical components. It consists in bombarding metallic surfaces with spherical shots to induce plastic deformation in the surface layer of the material. Recent studies have shown that, if applied with unconventional parameters, namely severe shot peening, it can be considered a severe plastic deformation surface treatment, able to strongly modify the microstructure of the surface layer of material by generating grains in the scale of nanometers. In this paper, different shot peening treatments with conventional and severe parameters were performed on aluminium 6063 alloy in order to assess the differences induced in the microstructure of the surface layer, and to evaluate their effects on fatigue behaviour. Rotating bending fatigue tests were performed on shot peened hourglass specimens. Specimens’ microstructure, surface roughness, microhardness and residual stress profiles were carefully characterized. The obtained results evidence the notable influence of shot peening parameters on surface layer microstructure, which at the same time influences fatigue behaviour.

スライディングモード制御を用いた柔軟鋼板の湾曲浮上統合制御

The electromagnetic levitation technology which an object grips and transport without contact is focused, and actively considered in various approach. Considering stability of levitated object, the levitation method which inclueds mechanical properties of levitated structure is also considered. Application of the levitation technology in manufacture process for thin steel plate is demanded for enhancement surface quolity of products. However, the elastic vibration of steel plate is excited because of flexibility, and prevent stable levitation. To solve this problem, we have proposed a levitation method for an ultrathin steel plate that is bent to the extent that the plate does not induce plastic deformation. It has been confirmed that vibrations are suppressed and levitation performance is improved. In this study, we applied sliding mode control theory to the bending levitation system using continuous model, and carried out levitation experiments. These results show that applying sliding mode control theory further improve levitation performance.

Insight into mechanics of AFM tip-based nanomachining: bending of cantilevers and machined grooves

Atomic force microscope (AFM) tip-based nanomachining is currently the object of intense research investigations. Values of the load applied to the tip at the free end of the AFM cantilever probe used for nanomachining are always large enough to induce plastic deformation on the specimen surface contrary to the small load values used for the conventional contact mode AFM imaging. This study describes an important phenomenon specific for AFM nanomachining in the forward direction: under certain processing conditions, the deformed shape of the cantilever probe may change from a convex to a concave orientation. The phenomenon can principally change the depth and width of grooves machined, e.g. the grooves machined on a single crystal copper specimen may increase by 50% on average following such a change in the deformed shape of the cantilever. It is argued that this phenomenon can take place even when the AFM-based tool is operated in the so-called force-controlled mode. The study involves the refined theoretical analysis of cantilever probe bending, the analysis of experimental signals monitored during the backward and forward AFM tip-based machining and the inspection of the topography of produced grooves.

Non-contact sheet forming using lasers applied to a high strength aluminum alloy

Laser beam forming (LBF) is a contactless mechanical process accomplished by the introduction of thermal stresses on the surface of a material using a laser in order to induce plastic deformation. In this work, LBF was performed on 1.6mm thick sheets of a high strength aluminum alloy, AA6013-T4 class by using a defocused continuous Yb-fiber laser beam of 0.6mm in diameter on the sheet top surface. The laser power and process speed were varied from 200W to 2000W and from 3 to 30mm/s, respectively. For these experimental conditions, the bending angle of the sheet ranged from 0.1° to 2.5° per run. In the highest bending angle condition, 1000W and 30mm/s, the depth of remelted pool was 0.6mm and the microstructure near the plate bottom surface remained unaltered. For the whole set of experimental conditions, the hardness remained constant at approximately 100 HV, which is similar to the base material. In order to verify the applicability of the method, some previously T-welded sheets were straightened. The method was efficient in correcting the distortion of the sheets with a bending angle up to 5°.

Performance evaluation of soil-embedded plastic optical fiber sensors for geotechnical monitoring

Based on the distributed fiber optic sensing (DFOS) technique, plastic optical fibers (POFs) are attractive candidates to measure deformations of geotechnical structures because they can withstand large strains before rupture. Understanding the mechanical interaction between an embedded POF and the surrounding soil or rock is a necessary step towards establishing an effective POF-based sensing system for geotechnical monitoring. This paper describes a first attempt to evaluate the feasibility of POF-based soil deformation monitoring considering the POF-soil interfacial properties. A series of pullout tests were performed under various confining pressures (CPs) on a jacketed polymethyl methacrylate (PMMA) POF embedded in soil specimens. The test results were interpreted using a fiber-soil interaction model, and were compared with previous test data of silica optical fibers (SOFs). The results showed that the range of CP in this study did not induce plastic deformation of the POF; therefore, the POF-soil and the SOF-soil interfaces had similar behavior. CP was found to play an important role in controlling the fiber-soil interfacial bond and the fiber measurement range. Moreover, an expression was formulated to determine whether a POF would undergo plastic deformation when measuring soil deformation. The plasticity of POF may influence the reliability of measurements, especially for monitored geo-structures whose deformation would alternately increase and decrease. Taken together, these results indicate that in terms of the interfacial parameters studied here the POF is feasible for monitoring soil deformation as long as the plastic deformation issue is carefully addressed.

Hot and cold regions during accumulative roll bonding of Al/Al2O3 nanofibre composites

Accumulative roll bonding (ARB) is a severe plastic deformation process invented in order to fabricate ultrafine- grained (UFG) materials. Having sub-micrometre sized or nano grains UFG materials generally have considerably higher strength than conventional materials with grains at micrometre length scale. Further increase in mechanical properties could be achieved by reinforcing UFG materials with nanoparticles or nanofibres. In this work two metal sheets were roll bonded to each other by inducing plastic deformation via the ARB process. The plates were then cut into two, stacked, and rolled again. Rolling was repeated multiple times. Observations and measurements were made in the hot and cold regions of the plate. In this study the aluminium matrix was reinforced with aligned and non-aligned Al2O3 nanofibres. The morphology of the reinforcement-matrix interphase and mechanical properties of the composites were studied. The microstructure of the material was investigated using scanning electron microscopy accompanied with quantitative microstructure analysis. It was demonstrated that the plastic deformation in the first cycle due to broken Al2O3 nanofibres continued in the second cycle. The Al2O3 nanofibres were embedded in the aluminium matrix surface area to improve the mechanical properties during the multiple cycle ARB process. In the cold regions micro-defects such as porosity and cracks were observed while in the hot regions no such defects were detected.

Modifications to an elasto-visco-plastic constitutive model for prediction of creep deformation of rock samples

Time-dependent features of rocks and rock masses, particularly soft rocks, may emerge in most tunnels, mines and underground constructions under different deviatoric stress levels. To account for the creep deformation of rocks associated with the wide range of stress levels, modifications are made to a visco-plastic model which was initially developed for large stresses in squeezing conditions. Firstly, the concept of plastic hardening behavior is adopted for both instantaneous and visco-plastic deformations of rocks to estimate the induced plastic deformation even at relatively low deviatoric stress levels. Secondly, the visco-plastic dashpot element is described as a function of the stress level to determine the secondary stage of creep during the unloading and reloading phases which are crucial in tunneling and underground.The governing equations of the proposed model are implemented in numerical finite difference code (FLAC), using its built-in FISH language for constitutive models and then applied to a series of laboratory creep tests presented in the literature. The presented discussion compares the numerical results relating to the modified model with the data on time-dependent deformation developed in rock specimens.

Effect of initial grain size on inhomogeneous plastic deformation and twinning behavior in high manganese austenitic steel with a polycrystalline microstructure

The grain size effect on the deformation twinning in a high manganese austenitic steel which is so-called TWIP (twining induced plastic deformation) steel was studied in order to understand how to control deformation twinning. The 31wt%Mn-3%Al-3% Si steel was cold rolled and annealed at various temperatures to obtain fully recrystallized structures with different mean grain sizes. These annealed sheets were examined by room temperature tensile tests at a strain rate of 10-4/s. The coarse grained sample (grain size: 49.6μm) showed many deformation twins and the deformation twinning was preferentially found in the grains in which the tensile axis is parallel near to [111]. On the other hand, the sample with finer grains (1.8 μm) had few grains with twinning even after the tensile deformation. The electron back scattering diffraction (EB SD) measurements clarified the relationship between the anisotropy of deformation twinning and that of inhomogeneous plastic deformation. Based on the EBSD analysis, the mechanism of the suppression of deformation twinning by grain refinement was discussed with the concept of the slip pattern competition between the slip system governed by a grain boundary and that activated by the macroscopic load.

Restrictions of stress measurements using the curvature method by thermally induced plastic deformation of silicon substrates

Within this study, the effect of plastic deformation of coated single-crystalline silicon substrates on stress measurement of hard coatings by the curvature method was illuminated. Silicon substrates with different thicknesses (380 and 500μm) and orientations ((100) and (111)), coated with TiN and TiAlN, were examined and compared to each other with respect to their high-temperature plasticity. The curvature was measured during thermal cycling and isothermal annealing. Coated samples were additionally annealed in vacuum and subsequently characterized using scanning and transmission electron microscopy. The presence of plastic deformation of the silicon substrate was confirmed after thermal exposure by the detected high dislocation density. The resolved shear stress in the 500μm thick substrate at 600°C was calculated to 25MPa, which is in the range of the critical value of silicon at this temperature. Plastic substrate deformation, corroborated by experimental and theoretical approaches, is thus a significant source of error in estimating residual stress from curvature measurements performed at elevated temperatures or applied to coatings with pronounced stresses grown at moderate/high substrate temperatures.

A mold-free laser shock micro-drawing forming process using Plasticine as the flexible support

In this paper, a laser-generated shock wave was used to induce plastic deformation of metallic foils using Plasticine as a flexible support. In this new micro-drawing process, the laser-generated shock wave and the Plasticine are used to replace the conventional metal punch and mold. By undergoing large plastic deformation under the laser-generated shock wave, Plasticine accurately keeps the shape of the deformed workpiece, thereby improving the forming quality. Moreover, this is a damage-free forming process because the Plasticine is softer than metal foils. The feasibility of this new drawing process was conducted experimentally on aluminum, cooper, and titanium foils. The thickness distribution at the cross-section of the work piece was studied to evaluate the risk of crack. Meanwhile, the arrays of craters were fabricated on titanium foils. The results show that mold-free laser shock micro-drawing forming is an effective method to fabricate controlled micro-craters on metallic foils.