Plastic Work Research Articles

Interplay between microstructure, micromechanical, and tensile properties in wire arc additive manufactured nickel-aluminum bronze: As-built and heat treated

The generalized hardness-strength relationship in additively manufactured materials may differ from that observed in cast/wrought materials. To investigate this, the present study focuses on wire-arc additive manufactured (WAAM) Nickel-Aluminum Bronze (NAB) in both its as-built state and three distinct heat-treated conditions. Tensile tests and nanoindentation hardness tests were conducted simultaneously to establish a correlation between hardness and strength. Additionally, a comparison is made between the cast-NAB material and WAAM-NAB in this article. By considering the variations in grain size (coarse vs. fine) and intermetallic compounds in the cast and WAAM-NAB materials (in their as-built and post-heat treated forms), the correlation factor is found to differ based on the specific manufacturing processes and heat treatments employed. This paper aims to develop empirical equations that account for the various influencing factors, including rigid plasticity and uniform plastic work hardening conditions. Moreover, the study reports several indentation-based quantitative variables, such as the plasticity index, elastic recovery, recovery resistance, and wear resistance index of the WAAM-NAB material. By providing a comprehensive analysis of these factors, this research contributes to a better understanding of the hardness-strength relationship and the associated material properties in WAAM-NAB.

Micromechanical Contrast of Ordos Basin Sandstone‐Mudstone Interbedded Layered Rocks

AbstractLayered rocks are heterogeneous media composed of multiscale minerals with contrasting geomechanical properties. It remains unclear how the mechanical responses of constituent minerals among different adjacent layers vary in a microscale. Based on the grid nanoindentation tests assisted by high‐resolution scanning electron microscopy and energy‐dispersive spectroscopy techniques, we quantified the mechanical responses of various minerals in an interbedded sandstone‐mudstone core sample and provided visual mineralogies and indentation patterns of different adjacent layers. Results show that the Young's modulus, hardness, and elasticity index of quartz and dolomite decrease, whereas their fracture toughness and plastic work ratio increase from the sandstone layer to the mudstone layer. Quartz displays elastic‐dominated deformations in the sandstone layer whereas transforms into medium‐plastic deformations in the mudstone layer. The mean values of Young's modulus, hardness, and elasticity index of quartz in the sandstone layer are 1.28, 2.00, and 1.56 times higher than that in the mudstone layer, respectively. Dolomite and phyllosilicate minerals show prominently plastic‐dominated deformations in each layer. When an indenter encounters multiple minerals simultaneously, the mechanical responses are determined by the softer phases and irregular indent impressions are generated. Shear and radical cracks are prone to occur in the elastic‐dominated minerals, while chipping damage is induced in the plastic‐dominated minerals. This work provides new insights and fundamental understandings in geomechanical properties contrasts in multilayered rocks, and can facilitate the geomechanical modeling and upscaling schemes in multilayered formations.

In Situ Prediction of Metal Fatigue Life Using Frequency Change

A reliable technique for rapid prediction of the remaining useful life (RUL) of components experiencing fatigue degradation is introduced. The approach is based on measuring the temperature signature of a component upon rapidly changing its operating frequency for a short period of time. The temperature variations caused by alterations in plastic work rate are correlated to the loading history. The efficacy of the approach is investigated by conducting a series of axial fatigue tests on stainless steel 316 specimens. The material characterization involves subjecting the material to a constant amplitude fatigue load at 4 Hz and 12 Hz frequencies. The operating frequency is temporarily adjusted to the characterization frequencies for a brief duration. During this period, the change in the slope of temperature rise is recorded. Subsequently, the operation frequency is reverted to its original state, and the remaining useful life is predicted based on the recorded data. The model provides predictions for operation frequencies of 6 Hz, 8 Hz, and 12 Hz, and notably, the error of predictions is consistently under 12% for all cases. The method allows the operator to reliably estimate the remaining usefulness for field applications without interrupting the operation.

A Numerical Prediction for Hole-Splitting Damage of DP Steels Based on Plastic Work Criterion Using a Polynomial Stress Potential

A Numerical Prediction for Hole-Splitting Damage of DP Steels Based on Plastic Work Criterion Using a Polynomial Stress Potential

Coupling effect of strain gradient strengthening and thermal softening on the microscale plastic behavior of metallic materials

Size effects and thermal effects together determine the microscale plastic response of metallic structures in high-integrated microelectromechanical systems (MEMS) at different temperatures. To investigate the microscale plastic behavior of metallic materials at different temperatures, a thermo-mechanical coupled microscale plasticity model is developed. In the mechanical part of this model, the framework of conventional plasticity theory is maintained, and the plastic strain gradient is introduced as an internal variable to increase the tangential hardening modulus without the introduction of higher-order stress and higher-order boundary conditions. The influence of temperature on the mechanical parameters (e.g. the yield strength) is calibrated by experiment results. In the thermal part of this model, the heat generation in the plastic deformation stage is calculated by the difference between the plastic work and the hardening stored energy influenced by the plastic strain gradient. Due to the strong nonlinearity of the coupled equations, a finite element solution algorithm that combines the radial return method and the staggered solution scheme is proposed. The effectiveness of this model and its solution algorithm is verified by comparisons with the experiment results and a numerical benchmark example. Finally, taking the tensile behavior of a plate with a hole in its center as an example, the coupling effect of strain gradient strengthening and thermal softening on the microscale plastic behavior of metallic materials is investigated. The results show that the microscale plastic behavior of metallic materials at high temperatures depends on the competition between thermal softening and strain gradient strengthening. Our study provides a theoretical basis and a reliable simulation method for the design of MEMS at different temperatures.

Microstructure-Based Two-Scale Simulation of Deformation and Fracture of SiCp/2009Al Composite

Accurately predicting the formability of composites is quite important for designing the materials and optimizing the processing parameters of such components. This paper presents a microstructure-based two-scale model to analyze the deformation behavior of the SiCp/2009Al composite during upsetting. The microstructure-based micro-scale model with a displacement boundary condition that was obtained from a macro-scale model can predict particle cracking, interface failure and matrix fracture by introducing the normal stress criterion, the maximum stress ratio criterion and the shear fracture model. The simulation results show that, during unidirectional upsetting, the crack initiates in the matrix, and then propagates in the matrix, the interface and the particle. Comparing with the unidirectional upsetting, the bidirectional upsetting results in a more uniform stain distribution and a smaller maximum strain, which prevent the initiation of the crack in the matrix. The simulation results compare well with the deformation and fracture patterns observed in experiment, indicating an effective way to optimise the plastic working and designing of composites.

Applying Anand versus Garofalo creep constitutive models for simulating sintered silver die attachments in power electronics

This paper aims to examine the thermomechanical response of sintered silver die attachments in power electronics using finite element analysis (FEA). In this work, several material parameters of the sintered silver bonds are investigated. Additionally, two common solder creep constitutive laws including Anand and Garofalo models are also studied. To ensure the fidelity of the simulation procedures, the finite element (FE) models are first correlated with digital image correlation data. Afterward, the FE models are utilized to examine the influence of the material and creep models on the die attach stresses, strains, and plastic works. The expected fatigue and lifetime predictions of the sintered silver layer are thoroughly discussed, accordingly. The results proved that the die attach layer mechanical response is highly driven by the material parameters and creep modeling procedures considered throughout the simulations. Thus, the resulting fatigue life is evaluated. Finally, a general modeling guideline for simulating thermomechanical response of sintered silver die attachments in power electronics are provided in great detail.

An experimental investigation of the tensile, fracture and microstructural characteristics of ABS/SBS reinforced with HNTs

AbstractThermoplastic composites are broadly used in many industries. Excellent mechanical characteristics are frequently required to achieve the appropriate properties for the applications. Therefore, the objectives of this study were (1) presenting an in‐depth analysis of the effects of styrene butadiene styrene (SBS) and halloysite nanotubes (HNTs) on the tensile and fracture properties of the thermoplastic composites based on acrylonitrile butadiene styrene (ABS), and (2) examining the relationship between the microstructure of the thermoplastic composites and their mechanical behavior. For these purposes, HNTs were utilized with four levels (0, 1, 3, and 5 wt%) and SBS was used with two levels (15 and 30 wt%). The tensile strength and modulus were reduced by adding SBS to 30 wt%; however, the elongation at break was increased by 30%. Furthermore, tensile strength and modulus, and elongation at break were improved by increasing HNTs up to 3 wt%. The results indicated the elastic work (we) and plastic work (βwp) rose by 29% and 10%, respectively, when 30 wt% of SBS was added to ABS. Furthermore, we and βwp rose by the addition of HNTs up to 3 wt%. To examine fracture mechanisms, field emission scanning electron microscope (FESEM) images of the fracture surface of the essential work of fracture (EWF) specimens were taken. Several voids are present in the compounds containing SBS, activating the plastic deformation mechanism. Based on the optimization process, the best strength, stiffness, and toughness balance was attained for the compound consisting of 15 wt% SBS and 1 wt% HNTs.Highlights The effects of HNTs and SBS on the fracture properties of polymer composites. The addition of SBS increased we, βwp, and the elongation at break. HNTs had a positive effect on the tensile strength and modulus, we, and βwp. The important mechanisms include plastic deformation and cavitation.

Enhanced cavitation erosion resistance of GX40CrNiSi25-20 cast stainless steels by surface TIG re-melting

This study aimed to reduce cavitation erosion effects by improving the surface properties of high-alloyed steel cast parts using the tungsten inert gas (TIG) surface physical modification technique. Local surface melting was performed at different linear energies (El = 4080–8880 J/cm) by varying the current between 100 and 200 A at a constant voltage of 10.2–11.1 V. Hardness increased from 210 to 390 HV5 when a TIG current of 150 A with a linear energy of El = 6630 J/cm was implemented.Using this technique, a surface layer with increased resistance to cavitation erosion was formed. This new surface absorbed large amounts of impact energy owing to a favourable combination of microstructural changes, leading to improved elastic and plastic properties, work hardening, cracking, and failure response. The cavitation erosion performance of the re-melted surface layer was analysed using a piezoceramic vibrating device according to the ASTM G32–2016 standard. Following TIG surface re-melting, the average penetration depth of erosion and the cavitation erosion rate increased by approxmately 6.8 times. Based on optical and electronic metallographic analyses, hardness measurements, and X-ray diffraction, it was shown that the morphology of the surface layer following cavitation erosion tests was affected. Microcraters tended to develop at locations where carbide particles from the alloying elements were previously present. At a current of 150 A, the depth of the microcraters reached values of approximately 15 μm; however, microcrater depth reached 10 μm in the austenite matrix. Based on these investigations, an understanding of the mechanisms that result in the improvement of the resistance to erosion by cavitation of cast high-alloy steels whose surfaces were re-melted using the TIG technique is developed.

Thermodynamically consistent strain hardening variable/driving force, inelastic stored energy and self-heating in dynamic plasticity

Accounting for self-heating and subsequent thermal softening in dynamic plasticity requires an accurate estimation of the mechanical dissipation rate which is by definition the difference between the plastic work rate and the inelastic stored energy rate. Yet, in constitutive modeling, the evaluation of the inelastic stored energy strongly depends on the adopted approach, viz. irreversible thermodynamics vs microstructure-motivated approach, and, whatever the approach, does not yet lead to realistic results in terms of self-heating. The aim of the present study is to attempt to conciliate both above mentioned approaches by building constitutive models that relate strain hardening, inelastic stored energy and self-heating in a consistent way. The models in question are developed in agreement with experimental results obtained on five high-strength steels.

A Numerical Evaluation of Forming Failure of an Aluminum Sheet due to Splitting Damage in Hole Expansion Process

Abstract The reduction of car body weight is the principal issue of car manufacturers for reducing fuel consumption. Aluminum alloys are attractive materials for the automotive industry because they have low density and adequate strength, but they may exhibit crack formation during manufacturing processes. Generally, crack formations emerge because of tool geometry and material anisotropy. Accordingly, determination of the forming limits of aluminum alloys is essential. The hole expansion test (HET) is a significant formability process used in the automotive industry because it gives information about the stretch-flangeability limits of the material. Edge splitting (edge fracture) is a failure type seen in HET, and it limits the stretch-flangeability of the material. Therefore, the prediction of edge splitting is an essential issue for engineers in the automotive industry. In this work, HET of AA6016-O aluminum alloy was simulated with the finite element (FE) method to assess the influence of yield functions on failure prediction in HET. To this end, Hill48, Yld91, and a homogeneous fourth-order polynomial type yield criteria (HomPol4) were selected to identify the anisotropic behavior of the sheet. Analyses were carried out in Marc commercial FE software, and the Hypela2 user subroutine was incorporated into FE code. Thickness distributions in the rolling direction (RD), diagonal direction, and transverse direction (TD) of the part and around the hole edge were also predicted, and it was observed that only the HomPol4 criterion predicted excessive thinning at two locations near the RD and TD, separately. On the other hand, Yld91 and Hill48 predicted lower strain levels when compared with HomPol4. Finally, plastic work distribution around the hole edge was considered, and the predictions were compared with the experimental damaged sample. This comparison showed that HomPol4 predicted a robust plastic work localization in RD, which is consistent with the damaged sample.

Determining large-strain metal plasticity parameters using in situ measurements of plastic flow past a wedge

We present a novel approach to determine the constitutive properties of metals under large plastic strains and strain rates that otherwise are difficult to access using conventional materials testing methods. The approach exploits large-strain plastic flow past a sharp wedge, coupled with high-speed photography and image velocimetry to capture the underlying plastic flow dynamics. The inverse problem of estimating material parameters from the flow field is solved using an iterative optimization procedure that minimizes the gap between internal and external plastic work. A major advantage of the method is that it neither makes any assumptions about the flow nor requires computational simulations. To counter the problem of non-unique parameter estimates, we propose a parameterization scheme that takes advantage of the functional form of the constitutive model and reformulates the problem into a more tractable form to identify plasticity parameters uniquely. We present studies to illustrate the principle of the method with two materials with widely different plastic flow characteristics: copper (strain hardening) and a lead-free solder alloy (rate sensitive and deformation history dependent). The results demonstrate the efficacy of the method in reliably determining the material parameters under high strain/strain rate conditions of relevance to a range of practical engineering problems.

Cruciform tension-shear test for sheet metal: Evaluation of methods for calculating plastic work

The tensile-shear test specimen devised by Kim et al. (Kim M, Ha J, Bonica S and Korkolis YP 2021 Proc. 13th Int. Conf. Technol. Plast. pp. 1961-1967) is used to evaluate methods for calculating the plastic work per unit volume of a metal sheet subjected to combined tension and shear. The deformation of the tensile-shear specimen is analysed using finite element analysis (FEA). In tension-shear deformation, a material element undergoes rigid body rotation as well as in-plane deformation. Therefore, methods for calculating the stress components and the incremental strain components with respect to the material coordinate system and the spatial coordinate system are discussed. It is confirmed that the plastic work per unit volume does not depend on the coordinate system adopted in the calculation as long as the same coordinate system is used to evaluate the stress components and strain increment components.

Investigation of resistance spot weld failure in tailor hot stamped assemblies

A novel experimental method, dubbed the “Mode I Caiman test”, is introduced to characterize spot weld failure and propagation within spot weld groups. The test configuration comprises a partially welded pair of channel sections subjected to Mode I tensile loading through an opening mode loading applied at the un-welded end of the channels. Experiments were performed considering hot stamped USIBOR® 1500-AS in a fully hardened condition (fully quenched) or in a tailored condition in which the strength of the welded flanged regions was altered using in-die heating (IDH). Both static and dynamic loading conditions are considered. The static loading utilized a conventional tensile frame while the dynamic experiments were performed on an instrumented crash sled at velocities of 7.5 m/s.A high speed thermal imaging camera was utilized to detect the temperature rise associated with plastic work during individual weld failure. This proved to be a rather novel and effective technique to detect weld failure and enabled tracking of weld failure propagation through the weld group for the different parent metal (flange) conditions.The experiments served to demonstrate the complex interaction between weld nugget, heat affected zone (HAZ) and parent metal strengths. For high parent metal strengths (fully quenched, martensitic condition), the welds exhibited interfacial and weld pull-out failure modes with rapid unzipping of the weld group resulting in relatively low energy absorption. In contrast, the lower strength tailored flanges exhibited a more stable (slower) failure propagation through the weld group and considerably higher energy absorption which is largely attributed to greater dissipation through deformation of the flange itself. Numerical simulations of the experiments were performed using spot weld models calibrated from single weld lap shear, cross tension, and coach peel experiments. The models captured the peak loads rather well, but predictions of rate of failure propagation within the weld line exceeded that seen in the experiments, pointing to the need for improved post-failure models for spot weld simulation.In automotive structures in which numerous welds are present, the amount of energy absorbed in weld failure can significantly affect the impact response of the structure. The Mode I Caiman test presents a new opportunity to calibrate the energy release rate of spot weld damage models to improve their accuracy when modelling spot welded connections involving multiple spot welds.

Nanomechanical characterization of the hydrogen effect on high strength steels

The effect of hydrogen charging on nanohardness (HIT), elastic work (Welast), and plastic work (Wplastic) was investigated using nanoindentation. To accomplish this, two high-strength low-alloy steels (AISI 4130 M and AISI 4137 M) were tested using electrochemical nanoindentation with different loading rates (5 mN/min and 15 mN/min). Additionally, a continuous multicycle (CMC) indentation loading profile was proposed to assess the hydrogen embrittlement (HE) effect on AISI 4130 M steel. Under a current density of 0.5 mA/cm2 and 5 mN/min loading rate, AISI 4137 M steel exhibited a 30.6% reduction in Welast and a 9.8% increase in HIT value. In contrast, under the same conditions, Welast increased by 5.0% for AISI 4130 M steel. For the CMC indentation tests conducted on AISI 4130 M steel, both HIT and Welast values were affected, as evidenced by a reduction between 7% and 10% in HIT and between 4% and 22% in Welast. The lower deformation rates resulting from long-term CMC-type indentations enable hydrogen to follow the dislocation movement. In the experimental setup under study, the hydrogen-induced softening caused by the shielding of the elastic fields was observed as a reduction in nanohardness.

Evaluation of ductile fracture criteria in combination with a homogenous polynomial yield function for edge splitting damage of DP steels

Abstract This study investigates the formability characteristics of dual phase steels (DP600 and DP800) under flange stretching conditions through hole expansion tests. The hole-splitting initiation was numerically predicted using ductile damage functions coupled with an orthotropic plasticity model. Therefore, a polynomial yield criterion coupled with three damage criteria, namely generalized plastic work, void growth model, and a shear ductile fracture model, is implemented into Marc software by the user defined material subroutine. Thus, the fracture stroke, hole expansion ratio, and fracture initiation location were estimated for both steels. The polynomial yield criterion could capture the anisotropic features of the dual phase steels. Furthermore, the stress triaxiality-based criteria were reasonably accurate in stretching limit predictions of both steels’ grades. Nevertheless, plastic work predicted the fracture strokes and hole expansion ratios noticeably lower than the experimental outcomes for both steels. In addition, all the numerical results captured the exact fracture initiation location for DP600, while a slight discrepancy was observed for DP800. All ductile fracture models pointed out the identical crack location, which shows the cruciality of the yield criterion for locating the fracture initiation in hole expansion test. Consequently, both void growth model and shear ductile fracture model showed accurate performances conforming to the stress triaxiality was found to be more dominant than the Lode parameter.

Investigation of high rate mechanical flow followed by ignition for high-energy propellant under dynamic extrusion loading

Investigating the ignition response of nitrate ester plasticized polyether (NEPE) propellant under dynamic extrusion loading is of great significant at least for two cases. Firstly, it helps to understand the mechanism and conditions of unwanted ignition inside charged propellant under accident stimulus. Secondly, evaluates the risk of a shell crevice in a solid rocket motor (SRM) under a falling or overturning scene. In the present study, an innovative visual crevice extrusion experiment is designed using a drop-weight apparatus. The dynamic responses of NEPE propellant during extrusion loading, including compaction and compression, rapid shear flow into the crevice, stress concentration, and ignition reaction, have been firstly observed using a high-performance high-speed camera. The ignition reaction is observed in the triangular region of the NEPE propellant sample above the crevice when the drop weight velocity was 1.90 m/s. Based on the user material subroutine interface UMAT provided by finite element software LS-DYNA, a viscoelastic-plastic model and dual ignition criterion related to plastic shear dissipation are developed and applied to the local ignition response analysis under crevice extrusion conditions. The stress concentration occurs in the crevice location of the propellant sample, the shear stress is relatively large, the effective plastic work is relatively large, and the ignition reaction is easy to occur. When the sample thickness decreases from 5 mm to 2.5 mm, the shear stress increases from 22.3 MPa to 28.6 MPa, the critical value of effective plastic work required for ignition is shortened from 1280 μs to 730 μs, and the triangular area is easily triggering an ignition reaction. The propellant sample with a small thickness is more likely to stress concentration, resulting in large shear stress and effective work, triggering an ignition reaction.

2次均質化法を用いた多結晶材料の圧縮変形における寸法依存性と加工条件の関係評価

In a hot steel rolling process, the rolling force and the strain distribution in a rolled material is strongly affected by the friction coefficient between the work roll and the rolled material and the rolling shape factor which is the ratio of the contact length between the work roll and the material to the material thickness. In this respect, many numerical attempts have been made to reveal their relationship. These simulations often suppose the homogeneity of the material because of simplicity. However, the recent researchers have suggested that the heterogeneity in microstructure can cause size effect on deformation behavior of polycrystalline material. In order to clarify the size effect in the rolling process, this study investigates the size effect on the deformation force and the strain distribution in the plane strain compression which is simple and similar to the flat rolling in effects of the friction coefficient and the shape factor, using the second-order homogenization-based finite element (2nd HMFE) simulations. Simulations are performed by two-dimensional 2nd HMFE with different friction coefficients, shape factors, work hardening parameters and size ratios between micro and macrostructures, which are related to strain heterogeneity in a deformed material. As a result, in case of the small friction coefficient, relatively uniform deformation tends to occur in the material, which results in small effects of the size ratio on deformation behavior. In contrast, in case of the large friction coefficient, size effects on the compression force and the strain distribution appears to be large when the shape factor of a deformed material approaches 1. It is considered to be because high strain gradient tends to reduce the plastic work in the microstructure and a deformation band in which the strain gradient is higher is formed in the material in such a case.

Study on Mass Erosion and Surface Temperature during High-Speed Penetration of Concrete by Projectile Considering Heat Conduction and Thermal Softening.

The mass erosion of the kinetic energy of projectiles penetrating concrete targets at high speed is an important reason for the reduction in penetration efficiency. The heat generation and heat conduction in the projectile are important parts of the theoretical calculation of mass loss. In this paper, theoretical models are established to calculate the mass erosion and heat conduction of projectile noses, including models of cutting, melting, the heat conduction of flash temperature, and the conversion of plastic work into heat. The friction cutting model is modified considering the heat softening of metal, and a model of non-adiabatic processes for the nose was established based on the heat conduction theory to calculate the surface temperature. The coupling numerical calculation of the erosion and heat conduction of the projectile nose shows that melting erosion is the main factor of mass loss at high-speed penetration, and the mass erosion ratio of melting and cutting is related to the initial velocity. Critical velocity without melting erosion and a constant ratio of melting and cutting erosion exists, and the critical velocities are closely related to the melting temperature. In the process of penetration, the thickness of the heat affected zone (HAZ) gradually increases, and the entire heat conduction zone (EHZ) is about 5~6 times the thickness of the HAZ.

Plastic neural network with transmission delays promotes equivalence between function and structure

The brain is formed by cortical regions that are associated with different cognitive functions. Neurons within the same region are more likely to connect than neurons in distinct regions, making the brain network to have characteristics of a network of subnetworks. The values of synaptic delays between neurons of different subnetworks are greater than those of the same subnetworks. This difference in communication time between neurons has consequences on the firing patterns observed in the brain, which is directly related to changes in neural connectivity, known as synaptic plasticity. In this work, we build a plastic network of Hodgkin–Huxley neurons in which the connectivity modifications follow a spike-time dependent rule. We define an internal-delay among neurons communicating within the same subnetwork, an external-delay for neurons belonging to distinct subnetworks, and study how these communicating delays affect the entire network dynamics. We observe that the neuronal network exhibits a specific connectivity configuration for each synchronised pattern. Our results show how synaptic delays and plasticity work together to promote the formation of structural coupling among the neuronal subnetworks. We conclude that plastic neuronal networks are able to promote equivalence between function and structure meaning that topology emerges from behaviour and behaviour emerges from topology, creating a complex dynamical process where topology adapts to conform with the plastic rules and firing patterns reflect the changes on the synaptic weights.