Strain Hardening Effect Research Articles

Experimental study on seismic behavior of high strength steel frames: Local response

In full-scale cyclic loading tests conducted by the authors on six one-bay two-story high strength steel moment frames, strains on surfaces of beams, columns and their joints were extensively monitored, and the shear distortions in east-side panel zones at both stories were recorded. The global responses of all specimens at the frame level were prepared and analyzed in the first companion paper. This paper deals with those local responses of members and joints under real boundary conditions in frame structures, which were expected to assist more accurate and reasonable assessment of their seismic behavior than individual tests on extracted specimens. Beams remained essentially elastic throughout all tests, while columns developed significant yielding and maximum moments at column bases that were 30% to 75% higher than the fully plastic moment depending on section slenderness. Compact columns of 460 MPa high strength steels exhibited superior cyclic behavior with stable energy dissipation, so did those panel zones that underwent inelastic deformation. Cover-plate connections finished all loading cycles in all specimens and were effective to reduce the risk of fracture at beam-to-column welds. Continuity plates might not be able to resist the seismic demand specified by current codes, since they fractured in one specimen with a demand-to-capacity ratio of 0.72, which was also the highest among all specimens. Plastic resistances of panel zones predicted by various codes except for the Chinese code, underestimated the experimental results due to the effect of strain hardening, while seismic demands on panel zones specified in various codes differed a lot. It was the Chinese code that both provided the lowest demand and overestimated the resistance, and thus resulted in the weakest panel zone design.

The Reduction Effect of Al-Cu Series 2024 on the Processing Rolled In Mechanical Properties

The industrial in Indonesia needs to improve the quality of goods produced so that it can provide satisfaction to consumers. Likewise in industries that work and process materials must have quality standards so that a material produced has good quality. Aluminum is one of the most widely used materials in the industrial sector after iron and steel. Aluminum can be combined with other metals such as Cu, Mg, Si, Mn, Zn, Ni, to add the characteristics of aluminum that you want to improve. Increased strength through the rolling process which varies the cross-section reduction (5%, 10%, 15%, and 20%), is intended to find out how much the strain hardening effect on the rolling process on the mechanical properties of Al-Cu alloys Based on the results of the study, it was found that plastic deformation through the rolling process can increase hardness, strength, and increase metal shaking. In Al-Cu alloy series 2024, the optimal reduction is 15% of the thickness of a 10 mm plate with a rolling temperature of 200 ° C. At the recrystallization temperature of the Al-Cu alloy series 2024, there is still a mechanism of metal strengthening due to strain hardening.

Study on Constitutive Relation of Nickel-Base Superalloy Inconel 718 Based on Long Short Term Memory Recurrent Neural Network

The high temperature tensile test of Inconel 718 under the conditions of deformation temperature of 950 °C–1100 °C and strain rate of 0.0005 s−1–0.1 s−1 was carried out, and its true stress–true strain curve was drawn. Through the analysis of the flow stress of Inconel 718 under different conditions, it can be seen that the high-temperature rheological behavior of Inconel 718 is affected by the coupling of strain hardening effect and dynamic softening effect, and has significant loading history correlation. By applying the stretched data, a long short term memory (LSTM) recurrent neural network was trained to characterize the constitutive relationship of Inconel 718. The experimental results show that the prediction results of the LSTM constitutive model are extremely consistent with the experimental data, which is significantly better than the modified Johnson–Cook (M-JC) model. Finally, high temperature tensile experiments under variable strain rates were carried out to verify the feasibility of the LSTM constitutive model in the complex loading and unloading stages.

Springback behavior and a new chord modulus model of copper alloy during severe plastic compressive deformation

Abstract The copper alloy in the unloading process after severe plastic compressive deformation (SPCD) exhibits obvious nonlinear stress-strain relationship and hysteresis behavior, and generates severe springback deformation. The severe strain hardening and softening effects occurring in the SPCD and the anisotropy of the material will affect the springback behavior of the material. In this paper, the samples obtained along the different directions (rolling direction, short-thickness direction, transverse direction, and 45° direction) of copper alloy hot-rolled plates were used to perform the quasi-static single pass compression tests with different deformation ratios (0.25 %–90 %). The springback behavior of the copper alloy under the SPCD was investigated. The effects of the strain hardening, strain softening and anisotropy on the springback behavior of the material were revealed. The variation relationships of the instantaneous tangent modulus and the chord modulus in unloading with stress and strain at different deformation stages (elastic stage, yield stage, strain hardening stage, and strain softening stage) were analyzed. A new chord modulus in a power exponential form was proposed. According to the unloading characteristic of the SPCD, the Yoshida-Uemori chord modulus model and the QPE model were modified. The applicability and accuracy of the unloading chord modulus models for the SPCD were evaluated and compared by using the power exponential chord modulus model, the modified QPE chord modulus model, the modified Yoshida-Uemori chord modulus model, and the Yoshida-Uemori chord modulus model, respectively. Besides, based on the proposed chord modulus model in a power exponential form, a 1-D E T model in a power exponential form was also proposed to describe the nonlinear unloading process and the variation of the slope of the unloading curves after the SPCD. The results indicated that the springback behavior of SPCD is obviously different from those of small plastic compressive deformation and elastic compressive deformation. The proposed chord modulus model in a power exponential form can accurately predict the chord modulus and springback strain in the unloading after the SPCD.

Interfacial and tribological properties of laser deposited TiOxNy/Ti composite coating on Ti alloy

In this work, a wear-resistant TiOxNy/α-Ti composite coating was deposited by laser cladding TiO2 powder onto Ti–6Al–4V in air. Dendritic TiOxNy reinforcements were synthesized in situ via reactions between Ti, TiO2 and N2. The partially-melted substrate mixed with the ceramic melt and formed α-Ti matrix that bonded chemically with the reinforcements. Stacking faults, induced by thermal stress, were found in the TiOxNy grains, which exerted a strain hardening effect. The coating had an average microhardness of 1417 HV0.3, four times that of Ti–6Al–4V. The wear resistance of the composite coating was 3.7 times that of Ti–6Al–4V, which was attributed to its high hardness and the strong TiOxNy/α-Ti and coating/substrate interfaces.

Microstructural and mechanical behavior of Al-Mg-Mn-Sc-Zr alloy subjected to multi-axial forging at room temperature

The as-homogenized Al-5.5 Mg-0.3Mn-0.2Sc-0.1Zr alloy with average grain size of 60 μm and coherent Al3(Sc,Zr) precipitates of 5 nm in diameter was deformed to an accumulative equivalent strain (∑ε) of 7.02 by multi-axial forging (MAF) in channel die at room temperature. The mechanical property and microstructure of the as-homogenized (∑ε = 0), 3rd (∑ε = 2.34), 6th (∑ε = 4.68) and 9th pass (∑ε = 7.02) samples were investigated. Results show that dynamic recrystallization was inhibited due to the pinning effect of AlxMn and Al3(Sc,Zr) precipitates. High density dislocation structure produced a remarkable strain hardening resulting a significant improvement of mechanical property at low equivalent strain (∑ε ≤ 2.34), while, the grain size changed little and the fine-grain strengthening effect was not obvious. Low-angle grain boundaries (LAGBs) formed gradually with increasing of equivalent strain as dislocation recombining, and developed into high-angle grain boundaries (HAGBs), resulting an obvious structure refinement at high equivalent strain. As a combined strengthening effect of strain hardening and grain boundary strengthening, the yield strength (YS) and ultimate tensile strength (UTS) increased to as high as 509 MPa and 597 MPa respectively when equivalent strain reached to 7.02.

Effect of solution treatment on slurry erosive wear performance of martensitic and nitrogen strengthened austenitic stainless steel

The present study shows jet-type slurry erosion behavior of 21-4N Nitronic and CA6NM martensitic steels. These steels were solution treated by the general procedure to improve their erosion performance. Microhardness was measured before and after erosion tests to study the effect of strain hardening. It was found that the strain hardening ability of the Nitronic steel is much higher than the martensitic steel. The cumulative weight loss was found lower for solution-treated Nitronic steel and comparatively higher for as-received CA6NM steel. The fractured surfaces were studied with SEM and found that the material loss was mainly due to fracture and deformation of the hard phases.

Influences of the constrained groove pressing on microstructural, mechanical, and fracture properties of brass sheets

Constrained groove pressing (CGP) was used for the production of fine-grained brass sheets in different conditions. The process was conducted up to two cycles on brass sheets at room temperature and then half cycle at the temperature of 200 °C. Optical microscopy (OM), scanning electron microscopy (SEM), microhardness measurement, and plane stress fracture toughness was used to investigate the microstructure, mechanical properties, and fracture behavior. Microhardness measurement showed the capability of the CGP process in increasing the hardness of the refined sheets. It also showed the inhomogeneity of the hardness along the thickness of the sample after the process. The Digital Image Correlation (DIC) technique was used to investigate the elastic and plastic factors of the sheets along with the major mechanical properties of samples. The results showed a slight increase and reduction in the Young modulus and Poisson’s ratios after the process, respectively. Moreover, after two CGP cycles applying half cycle at the temperature of 200 °C did not show any significant effect on these values. The strength coefficient was as like as yield and ultimate strengths increased by increasing the number of the passes. However, processing at a higher temperature of 200 °C showed lower values for the parameters, as mentioned earlier, compared to the specimens processed at room temperature. The strain hardening index experienced a major reduction after the CGP process due to the effects of strain hardening. The anisotropy coefficient, which plays a critical factor in the severe deformation of sheets, was increased after the CGP process. However, this ratio decreased in higher passes or elevated temperatures. The highest anisotropy coefficient was obtained after the first cycle of the process. Moreover, SEM observation of the fracture surface showed shearing ductile rupture mode in the processed samples rather than ductile mode due to appearing of small and elongated dimples.

Stress corrosion cracking and precipitation strengthening mechanism in TWIP steels: progress and prospects

AbstractTwinning-induced plasticity (TWIP) steels are increasingly receiving wide attention for automotive applications due to their outstanding combination of ductility and strength, which can largely be attributed to the strain hardening effect, formation of mechanical twins during straining, and the presence of manganese (Mn) as an alloying element. However, the premature cracking and sudden failure frequently experienced by the TWIP steels under the combined action of tensile stress and corrosion environment remain a challenge for many material scientists and experts up till now. Driven by this challenge, an overview of the stress corrosion cracking (SCC) susceptibility of high-Mn TWIP steels (under the action of both mechanical loading and corrosion reaction) is presented. The SCC susceptibility of the high-Mn TWIP steels is specifically sensitive to hydrogen embrittlement, which is a major factor influencing the SCC behavior, and is a function of the hydrogen content, lattice-defect density and strength level. Besides, the corrosion susceptibility to hydrogen embrittlement may be reduced by suppressing the martensite in the TWIP steels by carbon additions. This review further discusses in detail the precipitation strengthening mechanisms as well as the corrosion behavior of TWIP steel by mechanism.

The Effect of Material Properties on the Accuracy of Superplastic Tensile Test

Tensile testing is widely used for the mechanical characterization of materials subjected to superplastic deformation. At the same time, it is known that the obtained flow data are affected by specimen geometry. Thus, they characterize the specimen rather than the material. This work provides the numerical analysis aimed to study how the material flow behavior affects the results of tensile tests. The simulations were performed by the finite element method in Abaqus software, utilizing user-defined procedures for calculation of forces acting on the crossheads. The accuracy of tensile testing is evaluated by the difference between the input material flow behavior specified in the simulations and the output one, obtained by the standard ASTM E2448 procedure based on the predicted forces. The results revealed that the accuracy of the superplastic tensile test is affected by the material properties. Even if the material flow behavior follows the Backofen power law, which is invariant for the effective strain, the output stress–strain curves demonstrate significant strain hardening and softening effects. The relation between the basic superplastic characteristics and the tensile test errors is described and analyzed.

Comparative experimental study of the dynamic properties and adiabatic shear susceptibility of titanium alloys

Titanium and titanium alloys are prone to adiabatic shear failure when deformed at high strain rates due to their low coefficients of specific heat and thermal conductivity. Comparative study of the adiabatic shear susceptibility of titanium alloys are seldom reported in the literature. To further understand this topic, the mechanical response of five representative titanium alloys, i.e. commercially pure titanium (TA2, α), Ti-6.5Al–2Zr–1Mo–1V (TA15, near α), commercially Ti–6Al–4V (TC4, α+β), Ti–5Al–5Mo–5V–1Cr–1Fe (TC18, near β) and Ti–3Al–8V–6Cr–4Mo–4Zr (TB9, β), is characterized over a wide range of strain rates (ranging from 0.001 to 4000s−1) and temperatures (ranging from 293 to 673K). The findings of this experimental demonstrate that the yield stress of TA2 is the lowest, while it is the highest for TC18. The strain hardening effect of titanium alloys is prominent at low strain rate, while it may be decreased at high strain rates due to the presence of β-phase stabilizers. In addition, the mechanical behavior of titanium alloys is sensitive to strain rate and test temperature. The results also suggest that the formation of ASB is related to the applied strain rate and initial test temperature, and higher test temperature and strain rate promote the occurrence of adiabatic shear localization in dynamic deformation. Moreover, for titanium alloys, a lower strain-hardening coefficient and higher strength does not correspond to high sensitivity to adiabatic shear failure, and the dynamic failure energy, with its constant value, seems to be the best indicator of ASB failure. Furthermore, our results and analysis are important in enhancing the understanding of the dynamic properties and adiabatic shear susceptibility of titanium alloys. Based on this work, engineers can choose the optimal titanium alloy to fabricate components according to the service requirements to fully utilize the potential of the material.

Three-Dimensional Atomic Structure of Grain Boundaries Resolved by Atomic-Resolution Electron Tomography

Summary Grain boundaries (GBs) determine the properties of polycrystals, and tailoring the GB structure offers a promising method for the discovery and engineering of new materials. However, GB structures are far from well understood because of their structural complexity and limitations of conventional projection imaging methods. Here, we decipher three-dimensional atomic structure and crystallography of GBs in nanometals using atomic-resolution electron tomography. Unlike conventional descriptions, whereby they are either straight or curved planar planes with one-dimensional translational symmetry, we show that the high-angle GBs completely lose translational symmetry due to undulated curvature related to configurations of structural units. Moreover, we directly visualize kinks and jogs at the single-atom scale in dislocation-type GBs and investigate their mobilities. Our findings bring new insights to the conventional wisdom of GBs and show the importance of developing methods to include the non-planar nature of GBs to statistically evaluate the behavior of GBs in modeling studies.

Hydroforming analysis of exhaust pipe connectors

Abstract In this work, a hydroforming analysis of an exhaust pipe clamp adaptor made of galvalume steel was performed. Deformation and failure of galvalume exhaust pipe connectors and its coatings via the hydroforming process were studied. An explicit type (LsDyna) numerical analysis approach was adapted for the development of the hydroforming process. Pressure rate, unconstraint length, residual stress, strain hardening, and spring-back effects were considered in the analysis. The failure of tubular parts was evaluated via a forming limit diagram (FLD) according to Hill- Swift criteria. The hydroforming process was developed according to three models, which are found in the safety forming region of FLD studies. Minimum thickness values obtained from the experiments were compared with finite element analysis (FEM). The maximum percentage thinning ratio in the tubular section was more than 18 - % at 65 MPa internal pressure. The relationship between thickness reduction at plastically work hardening regions and residual stress was discussed. The deformation characteristics of the produced connector headers were also analyzed by scanning electron microscopy (SEM) and micro Vickers hardening measurements. The FEM analysis and FLD examination indicated that the failure did not occur in hydroformed specimens, whereas damage was observed at coated’ plastic work regions through microscopical investigation.

Temporary/Permanent Dual Cross-Link Gels Formed of a Bioactive Lactose-Modified Chitosan.

Mounting evidences have recognized that dual cross-link and double-network gels can promisingly recapitulate the complex living tissue architecture and overcome mechanical limitations of conventional scaffolds used hitherto in regenerative medicine. Here, dual cross-link gels formed of a bioactive lactose-modified chitosan reticulated via both temporary (boric acid-based) and permanent (genipin-based) cross-linkers are reported. While boric acid rapidly binds to lactitol flanking diols increasing the overall viscosity, a slow temperature-driven genipin binding process takes place allowing for network strengthening. Combination of frequency and stress sweep experiments in the linear stress-strain region shows that ultimate gel strength, toughness, and viscoelasticity depend on polymer-to-genipin molar ratio. Notably, herewith it is demonstrated that linear stretching correlates with strain energy dissipation through boric acid binding/unbinding dynamics. Strain-hardening effect in the nonlinear regime, along with good biocompatibility in vitro, points at an interesting role of present system as biological extracellular matrix substitute.

Theoretical and numerical analysis of a new energy-absorbing rock bolt with controllable constant resistance and large displacement

To provide an effective support device for dealing with the instability problems in geotechnical engineering, this paper proposes a new energy-absorbing rock bolt based on the existing energy-absorbing devices, called compression-expansion-friction bolt (abbreviated as the CEF bolt). The CEF bolt mainly consists of two parts, a variable-diameter tube and a hollow cone attached at the distal end of the bar. Controllable constant resistance and large displacement are the characteristics of the CEF bolt. The constant resistance was generated by the expansion of the tube under the compression of the cone, as well as the friction between the tube and cone. And the large displacement was provided by the sliding of the cone relative to the tube. A theoretical model was developed to predict the constant resistance by taking into account the effect of material strain-hardening. Based on the energy conservation law, the effect of shear deformation was also considered. Further, the current model was formulated as three forms to consider different conditions. The predictions of the current theoretical model were in good agreement with existing experimental data. An experimentally validated finite element model was established to study the effects of main parameters on the constant resistance of the CEF bolt, such as cone angle, tube wall thickness, friction coefficient, expansion ratio and the strain-hardening property of the tube. The results of numerical simulation and theoretical analysis show that the constant resistance was directly proportional to the tube wall thickness, friction coefficient, expansion ratio and the strain-hardening modulus of the tube. But the constant resistance increased first and then decreased with respect to the cone angle, with an inflection point existed between 5° and 10°. The shear stress distribution and the deformation of the tube were investigated as well. According to the shear stress distribution, the zone under expasion of the tube can be divided into three characteristic areas: stress concentration area, smooth transition area, and stress re-concentration area. In addition, compared with the large number of experimentally validated numerical results, the wide applicability and sufficient accuracy of the current theoretical model were verified. By taking the derivative of the current theoretical model, the location of the inflection point can be obtained. These results can provide theoretical basis for the design and field application of the CEF bolt, as well as the similar structure.

Effects of finish rolling temperature and yield ratio on variations in yield strength after pipe-forming of API-X65 line-pipe steels

Flattened plates often show the lower or higher yield strength than initial leveled plates because tensile and compressive strains are repeatedly experienced at outer and inner walls during the pipe-forming and flattening, but reasons for the yield-strength variation after the pipe-forming are not sufficiently verified yet. In this study, ten line-pipe steels were fabricated by controlling alloying elements and finish rolling temperatures (FRTs), and the yield strength of pipe-flattened steel plates was predicted by using cyclic simulation tests, based on competing contributions of Bauschinger effect (BE) and strain hardening (SH) effect quantified from yield drop (YD) and yield rise (YR) parameters, respectively. High-FRT-treated steels (H steels) showed the lower BE and the higher SH than low-FRT-treated steels (L steels), thereby resulting in the smaller yield-strength reduction. This lower BE in the H steels was caused by the lower total boundary density, while the higher SH was caused by the higher fraction of granular bainite. According to the SH analyses between the YR parameters obtained from cyclic simulation tests and the yield ratios obtained from ordinary tensile tests, the decrease in yield-strength reduction with decreasing yield ratio was not attributed to the increase in ordinary tensile SH but to the increase in YR parameter.

Influence of Surface Texture and Composition on Graphene Growth by Chemical Vapor Deposition on Cu–Ni Alloys for Field Emission Application

The present investigation is aimed to find a thread between various surface textures of polycrystalline Cu–Ni alloys, in cold-rolled and annealed conditions, and the nature of graphene, grown by the chemical vapor deposition (CVD) method, on these substrates. High-quality graphene grown on Cu–Ni alloys was transferred to various nanostructures, such as CuO nanorods and carbon nanotubes, for field emission application. In this work, Cu–Ni (100Cu–0Ni, 84.65Cu–15.35Ni, 72.6Cu–27.4Ni, and 63Cu–37Ni) alloy buttons were prepared by arc melting, and texture in the samples were engineered by cold rolling (plastic deformation) and annealing (recrystallization) processes. Study of surface texture by X-ray method demonstrates characteristically different deformation and recrystallization texture components, compared to conventional rolling and annealing textures. The evolution of texture has been explained based on the effects of surface friction, shear stress, and addition of Ni. Unusual appearance of {111} orientations, though less in volume, after annealing at 1000 °C, was observed in Cu–Ni alloys through the suppression of cube texture component. The underlying deformation and recrystallization mechanisms are explained through the changes in strain hardening, extended recovery, and continuous recrystallization effects. The effects of Ni content are correlated with the number of graphene layers, while an increase in the fraction of {111} orientations could be linked with defect density in graphene layers. Results of the present study will be motivating for selection of various polycrystalline Cu–Ni alloys, with different surface textures, for controlling quality of graphene, synthesized by the chemical vapor deposition method.

Mechanical properties of 1670 MPa parallel wire strands at elevated temperatures

High-strength prestressing steel cables serve as main load-bearing components for cable-supported structures, and exposure to high temperatures may result in their prestress loss, leading to failure and even collapse of such structures. This paper experimentally investigates the mechanical properties of 7-wire parallel wire strands with a tensile strength of 1670 MPa. The thermal elongation tests and steady-state tensile tests are conducted on 39 strand specimens at different target temperatures. The complete stress-strain curves including rupture strain are obtained by using charge-coupled device camera systems. The temperature-dependent thermal strain, Young’s modulus, proportional limit, effective yield strength, ultimate strength, ultimate strain and rupture strain are recorded and compared to EC2, ACI 216 and other existing test data. The test results show that parallel wire strands experience obvious strain hardening before 300 °C, and their ductility is significantly improved after 400 °C. It is reasonable to define effective yield strength as the stress at a total strain of 2%. It is found that the existing design code and test data on single wires and twisted strands cannot be directly used for parallel strands. The EC2 provides conservative predictions for ultimate strain, proportional limit, yield strength of parallel wire strands, but fails to capture the full range of stress-strain curves of parallel strands due to ignoring strain hardening effect and underestimating rupture strain. The ACI 216 provides unconservative predictions for reduction factors of ultimate strength of parallel strands. Parallel wire strands have higher thermal strain, higher ultimate strain, higher rupture strain, lower reduction factor of proportional limit than single wires and twisted wire strands. Finally, calculation methods are proposed to mathematically determine the thermal strain, stress-strain curve and reduction factors of these properties, and dividing the stress-strain relationship into elastic, plastic, necking and rupture stage.

Strain hardening analysis and modelling for sintered Al-Cu-TiC preforms with varying process parameters during cold upsetting

In sintered preforms, the presence of porosities are unavoidable; however, subjected to further deformation, preforms not only show closure of pores but as well as hardens the matrix. Both these phenomenon compliments each other in strain hardening effect, eventually its mechanical characteristics. However, in addition to the deformation, the process parameters also play a prominent role in influencing the strain hardening behaviour. Thus, while it is imperative to establish strain-hardening characteristics for the chosen composition under various process parameter influence, the modelling of the same is also inevitable to design preform for the desired characteristics. In the present investigation, Al with 4.5%Cu preforms has been synthesised through powder metallurgy process, in which, the process parameters such as, weight percentage of TiC, aspect ratio, initial density and the lubricant are varied to two different levels. The complete experiment has been formulated using 24 factorial design; however, it is performed in random order. The study is focused on evaluating strain-hardening characteristics of chosen composition under the influence of process parameters. In addition, the process parameters are modelled using Yates algorithm, and the applicability of the model is ensured through regression analysis and model adequacy test.

Hydroforming analysis of exhaust pipe connectors

Abstract In this work, a hydroforming analysis of an exhaust pipe clamp adaptor made of galvalume steel was performed. Deformation and failure of galvalume exhaust pipe connectors and its coatings via the hydroforming process were studied. An explicit type (LsDyna) numerical analysis approach was adapted for the development of the hydroforming process. Pressure rate, unconstraint length, residual stress, strain hardening, and spring-back effects were considered in the analysis. The failure of tubular parts was evaluated via a forming limit diagram (FLD) according to Hill- Swift criteria. The hydroforming process was developed according to three models, which are found in the safety forming region of FLD studies. Minimum thickness values obtained from the experiments were compared with finite element analysis (FEM). The maximum percentage thinning ratio in the tubular section was more than 18 - % at 65 MPa internal pressure. The relationship between thickness reduction at plastically work hardening regions and residual stress was discussed. The deformation characteristics of the produced connector headers were also analyzed by scanning electron microscopy (SEM) and micro Vickers hardening measurements. The FEM analysis and FLD examination indicated that the failure did not occur in hydroformed specimens, whereas damage was observed at coated’ plastic work regions through microscopical investigation.