Void Damage Research Articles

Plastic deformation and damage modeling of AA7075 synthetic 3D microstructure created using generative AI

3D microstructures provide valuable insight into material behavior which is essential in elucidating microstructural phenomena, such as particle morphology and void damage, and consequent macroscopic material response. However, creating 3D microstructures is extremely laborious and expensive, requiring complex microstructural characterization and imaging techniques such as Focussed-Ion Beam based Scanning Electron Microscopy (FIB-SEM) or X-ray Computed Tomography (XCT). To this end, synthetic 3D microstructures were rapidly generated from orthogonal 2D images using SliceGAN, which proved a practical and cost-effective method. In this study, multiple synthetic microstructures of AA7075-O, a complex microstructure of various strengthening precipitates within a softer aluminum matrix, were post-processed, meshed, and modeled for different damage behavior in FEA using advanced constitutive material models. Subsequently, the synthetic and real microstructures were qualitatively and quantitatively analyzed for their elastoplastic deformation and ductile void damage responses.This study illustrates the viability of an integrated AI-FE methodology in studying microstructural micromechanics, demonstrating that synthetic microstructures exhibited a very similar stress-strain response, especially when using a free boundary condition, and comparable stress distribution and void damage, albeit with some discrepancies. Also, it emphasizes the influence of particle morphology on strength and damage, where highly irregular particles play a dual role in increasing strain hardening by restricting matrix flow at the cost of increased ductile damage induced by decohered particles. Lastly, the more advanced FE models, with multiple voiding mechanisms, reduced the discrepancy between real and synthetic microstructures compared to simpler models

Study of the dynamic impact spalling of ductile materials based on Gurson-type phase-field model

The formation of void damage and spalling failure in ductile metallic materials under strong impact is a well-established phenomenon. In aerospace and defense technology engineering design, understanding the spalling failure process and related mechanisms is of utmost importance. This paper develops an explicit Gurson-type phase-field model that can simulate the void evolution and spalling damage of three-dimensional ductile metallic materials under high-velocity impacts based on the study of Aldakheel et al.. The model incorporates the Gurson-type void evolution equation and the phase-field approach while taking into account the pressure-dependent bulk modulus and inertia effects. This model is used to study the main processes and mechanisms of impacted layer cracking of metals in different dimensions. Meanwhile based on the study of complex spallation cracking processes in metals in two and three dimensions, observing and proposing the formation mechanism of complex spallation cracking modes in materials due to lateral and edge (base angle) rarefied effects.

Assessing gradient parameters for damage control in notched plates: Finite element analysis of locally functionally graded materials using the Gurson-Tvergaard-needleman (GTN) model

This study investigates functionally graded materials (FGMs) as reinforcement for notched plates prone to crack propagation. Using a novel meshing technique and the Gurson-Tvergaard-Needleman damage model within ABAQUS-Explicit, we explore how various gradation parameters affect material damage under stress. The model, incorporating Von Mises stress theory and Voce hardening law, simulates plastic flow and progressive damage from void dynamics. Validated against experimental data, our findings reveal that local gradation parameters significantly influence void damage and structural performance of notched components. This research provides crucial insights into FGMs' potential to enhance structural integrity in engineering applications involving notched structures.

Monitoring method of solder layer void damage of IGBT module based on transfer function

Monitoring method of solder layer void damage of IGBT module based on transfer function

Unraveling the transformation of ductile damage mechanisms of void evolution and strain localization based on deformation heterogeneity

This study delves into the ductile damage mechanism via exploring the intrinsic nature of the transformation of void and strain localization induced damages. In tandem with this, tensile experiments were conducted by using ductile metals of pure titanium and austenite steel with different grain sizes (d¯) and sample thicknesses (t). Various damage behaviors were generated: the void damage (Dv) in which the damage is induced by voids and their evolution, the strain localization induced damage (Dl) in which damage is controlled by localized deformation, and their mixed mode. Examinations of damage characteristics show a transformation from Dl to Dv with the increase of t/d¯ or hardening. To identify the decisive factor behind the mechanism, crystal plasticity finite element simulations were performed, and the grain-level non-homogeneous deformation was carefully examined. The materials with severe inhomogeneous deformation were found to have fewer voids, while the ones with more uniform deformation possessed evident void growth. Deformation heterogeneity was thus identified as a pivotal factor for the Dl - Dv transformation. The change of micro-defect configuration of void and grain boundary (GB) with deformation heterogeneity was discovered to be the underlying cause. In the Dv case, the large number of strain localization zones penetrating within the bulk promotes void nucleation and growth from vacancies and dislocations. The Dl case, on the other hand, gets more new GBs but smaller number of voids during deformation. The larger continuous strain localization zone facilitates the dislocation-consuming process of GB formation, resulting in the difficulty of void formation. Additionally, a characteristic parameter representing the deformation heterogeneity degree was defined. A Dl - Dv paradigm, which involves the change of damage mode and micro-defect configuration with deformation heterogeneity, and the characteristic parameter was established. The paradigm was validated to have a wide applicability with its efficiency in interpreting extensive damage phenomena. These explorations are expected to add new insights into the understanding of damage mechanism and support the development of a unified damage prediction platform.

Study on the Deformation and Fracture Mechanisms of Plastic Metals Considering Void Damage

Fracture initiation in plastic metals is attributed to the development of voids. Analyzing the nucleation and growth processes of voids facilitates the study of plastic deformation and fracture mechanisms in metal materials. Uniaxial tensile tests were conducted on two high-quality carbon structural steels, and the microfracture surface morphology of the tensile specimens was observed by using a scanning electron microscope (SEM). From the perspective of vacancy condensation, the nucleation mechanism of voids in the absence of inclusions or particles was analyzed. Based on the continuum damage mechanics theory and the Rice–Tracy (R-T) model, a damage parameter considering the void volume fraction was derived, and a plastic potential function, hardening curve, and constitutive model for the plastic deformation process of the plastic metal material were established. Based on the uniaxial tensile test data of the two sheets of high-quality carbon steel, the strain range data in the hardening stage were converted into true stress–plastic strain data, and the established hardening curve was used to fit the true stress–plastic strain data. The results showed good agreement between the established hardening curve and the experimental results, which effectively reflected the deformation process of ductile fractures in plastic metal materials.

Multiscale modeling of particle-induced damage in AA7075 aluminum sheet at large plastic strains

Large plastic deformation and ductile damage in precipitation hardening aluminum alloy AA7075 is driven by plastic flow in the vicinity of particles as well as fracture and decohesion of second phase particles embedded in the matrix. The current work investigates the deformation and damage characteristics of Fe-rich intermetallic particles, and η and θ precipitates in AA7075-O sheet. A multiscale model simulation methodology is presented and applied to analyze large-scale plastic deformation and damage characteristics. The methodology utilizes nanoscale molecular dynamics simulation to obtain matrix-particle interface strength properties and Weibull statistics to capture experimental fracture characteristics of particles. The above sub-models are incorporated within a 2-D real particle microstructure-based finite element model to conduct a comparative study of the roles of decohesion and fracture in the development of plasticity and void damage in AA7075-O sheet. In addition, in-situ SEM uniaxial tensile tests are carried out to assess the effectiveness of the simulation methodology and to compare the experimental and numerical results. Post-test high resolution X-ray computed tomography (HR-XCT) was also carried out to qualitatively observe particle-induced voiding in the material. The numerical methodology is shown to capture well the experimental trends in damage evolution of the individual particles. It is observed that particle damage is a function of inherent particle properties, their morphological features, and matrix strain localization characteristics. Larger-size Fe-rich particles are observed to undergo damage at an earlier stage, and consequently, affect the strain localization characteristics the most. In contrast, η precipitates are found to be most resistant to particle damage, followed by θ precipitates. Higher stresses inside strain localization bands, caused increased void damage initiation and growth of η and θ precipitates. Overall, particle fracture is observed to be marginally higher compared to particle decohesion, irrespective of the particle type.

Effect of Solder Layer Void Damage on the Temperature of IGBT Modules.

Solder layer void is one of the main failure causes of power semiconductor devices, which will seriously affect the reliability of the devices. In this study, a 3D model of IGBT (Insulated Gate Bipolar Transistor) packaging was built by DesignModeler. Based on ANSYS Workbench, the influence of void size, location, solder layer type, and thickness on the temperature distribution of the IGBT module was simulated. The results show that the larger the void radius, the higher the temperature of the IGBT module. The closer the void is to the center of the solder layer, the higher the temperature of the module. The void on the top corner of the solder layer had the greatest impact on the junction temperature of the IGBT module, and the shape of the void is also one of the factors that affect the temperature of the module. The denser the void distribution, the higher the temperature of the module. The temperature of the IGBT module was reduced from 62.656 °C to 59.697 °C by using nanosilver solder paste, and the overall heat dissipation performance of the module was improved by 5%. The temperature of the module increased linearly with the increase in solder layer thickness, and the temperature increased by 0.8 °C for every 0.025 mm increase in solder layer thickness. The simulation results have a guiding significance for improving the thermal stability of IGBT modules.

Influence of void damage on the electromechanical impedance spectra of Single Lap Joints

Adhesively bonded joints are susceptible to a variety of damage sources, which may be of difficult detection with current Non-Destructive Testing (NDT) methods. Structural Health Monitoring (SHM) techniques, such as the Electromechanical Impedance Spectroscopy (EMIS), aims to outpace NDT by continuously monitoring structures for defects. However, given the complexity of adhesive joint structures, EMIS capability for damage detection still needs to be thoroughly studied. In this manner, electrical impedance measurements were done to Single Lap Joints (SLJ), with both a modified epoxy adhesive and Pressure Sensitive Adhesive (PSA) for void detection. Void defects could not be detected on adhesive joints with the PSA but, in the case of joints with the modified epoxy adhesive, impedance signatures were significantly altered by the presence of both the artificially created void, and by a second damage source caused during the SLJ manufacture. Experimental measurements from modified epoxy joints were compared with simulation results, yielding good approximation when considering the effect of the second source of damage. An approximation of the mechanical impedance was also computed using numerical results from the pristine SLJ model. In this manner, it is possible to detect damage in the adhesive layer of SLJs with electrical impedance measurements from EMIS.

Strain localization and damage development during elevated temperature deformation of AA7075 Aluminum sheet

Elevated temperature forming of AA7075 aluminum alloy is of considerable interest in the automotive industry due to its potential for light weighting and several other environmental benefits. This study presents elevated temperature uniaxial tensile deformation and damage behavior of AA7075-W sheet through a set of experiments at the microstructural scale. A multi-scale experimental methodology consisting of in-situ SEM tensile testing, use of micro digital image correlation (µ-DIC) method for obtaining strain field at the microstructural scale and post-test X-ray computed tomography was adopted with temperature held constant at 300°C and 400°C. The deformation temperature affected the precipitate formation and their distribution and subsequently the precipitate-induced void damage development in the material. At 300°C, precipitates as well as precipitate free zones were formed at the grain boundaries during heating and following deformation. Intergranular void initiation and catastrophic void coalescence with relatively small void growth occurred along the grain boundaries during plastic straining resulting in intergranular fracture and poor ductility at this temperature. In contrast, at 400°C, fewer intergranular precipitates were formed during heating and deformation resulting in delayed void nucleation during plastic straining. The diffuse necking occurred earlier with significant void growth occurring during the long regime of diffuse necking with very little evidence of void coalescence leading to considerably higher ductility at fracture. The final fracture occurred due to transgranular microcrack formation and propagation at this temperature.

Features of management of patients with ankle bursitis

Bursitis is an inflammatory process that affects the joint capsule located between the bones and tendon fibers. In the normal state, the joint capsule is filled with synovial fluid the main function of which is to provide hydraulic lubrication for the normal sliding of the tendon along the bone in order to void damage to the tendon fibers. Depending on the location of the lesion of a particular anatomical region, there is bursitis of the shoulder joint (supracromial, subacromial, subdeltoid, subcoracoid forms), elbow joint, knee joint (prepatellar, suprapatellar, infrapatellar bursitis), the Achilles tendon bursitis, etc. Depending on the etiology of the lesion, specific bursitis caused by a certain type of pathogen and non-specific bursitis, most often of an autoimmune nature, are distinguished. Bursitis of the ankle joint can occur against the background of mechanical damage as a result of an injury, or it can develop against the background of gout or excessive load on the ankle joint. The main clinical manifestations of bursitis include pain, limited mobility, swelling, fever, and redness in the area of the affected joint. The tactics of treating ankle bursitis depends on its cause: antibiotic therapy is indicated for an infectious lesion; as for a traumatic injury, it is first necessary to ensure the immobilization of the affected limb, followed by the prescription of anti-inflammatory drugs; in autoimmune processes, doctors resort to the use of cor ticosteroids.

Study on Ductility Failure of Advanced High Strength Dual Phase Steel DP590 during Warm Forming Based on Extended GTN Model

Under warm forming, the damage parameters of extended GTN model are easily affected by temperature, and the failure of materials under warm forming is less studied by using this model. In this paper, based on the extended GTN model, the damage parameters of DP590 at different temperatures are determined by experiment and numerical simulation, studying the trend of damage parameters changing with temperature. Through the analysis of shear specimens at different angles and temperatures, we studied the changes in shear damage and void damage under different conditions, discussing the influence of shear damage and void damage on competitive fracture failure under warm forming. We modify the damage by using a function based on stress triaxiality, and present a competitive failure equation considering temperature and stress triaxiality. It is found that the extended GTN model can be applied to the failure study of DP590 steel under warm forming.

Effects of Freeze-Thaw Cycles on the Internal Voids Structure of Asphalt Mixtures.

Freeze–thaw cycle is one of the main distresses of asphalt pavement, and the law of freeze–thaw damage has always been an important topic. In this paper, X-ray computed tomography (CT) of asphalt mixture before and after freezing and thawing was carried out, and its two-dimensional (2D) digital image was recognized. Firstly, the eigenvalues of internal voids of asphalt mixture are extracted. Then the distribution of internal voids was analyzed. Finally, the evolution law of internal voids was summarized. The research results show that the characteristic mean value of the 9th cycle is the irreversible limit of freeze–thaw damage, and the non-resilience after the large void area increases is the fundamental reason for the accumulation of freeze–thaw damage. The source of void damage shifts from large voids to small voids, and the middle-stage is a critical stage of freeze–thaw damage. This work quantitatively evaluates the internal freeze–thaw damage process of asphalt mixture, and a morphological theory of the evolution of void damage based on an equivalent ellipse is proposed, which is helpful for better understanding the freezing–thawing damage law of asphalt pavement.

Big data mechanism of railway tunnel base void and degradation damage based on discrete element method

Big data mechanism of railway tunnel base void and degradation damage based on discrete element method

Big data mechanism of railway tunnel base void and degradation damage based on discrete element method

Big data mechanism of railway tunnel base void and degradation damage based on discrete element method

Dynamic Softening and Hardening Behavior and the Micro-Mechanism of a TC31 High Temperature Titanium Alloy Sheet within Hot Deformation.

TC31 is a new type of α+β dual phase high temperature titanium alloy, which has a high specific strength and creep resistance at temperatures from 650 °C to 700 °C. It has become one of the competitive candidates for the skin and air inlet components of hypersonic aircraft. However, it is very difficult to obtain the best forming windows for TC31 and to form the corresponding complex thin-walled components. In this paper, high temperature tensile tests were carried out at temperatures ranging from 850 °C to 1000 °C and strain rates ranging from 0.001 s−1 to 0.1 s−1, and the microstructures before and after deformation were characterized by an optical microscope, scanning electron microscope, and electron back-scatter diffraction. The dynamic softening and hardening behaviors and the corresponding micro-mechanisms of a TC31 titanium alloy sheet within hot deformation were systematically studied. The effects of deformation temperature, strain rate, and strain on microstructure evolution were revealed. The results show that the dynamic softening and hardening of the material depended on the deformation temperature and strain rate, and changed dynamically with the strain. Obvious softening occurred during hot tensile deformation at a temperature of 850 °C and a strain rate of 0.001 s−1~0.1 s−1, which was mainly caused by void damage, deformation heat, and dynamic recrystallization. Quasi-steady flowing was observed when it was deformed at a temperature of 950 °C~1000 °C and a strain rate of 0.001 s−1~0.01 s−1 due to the relative balance between the dynamic softening and hardening. Dynamic hardening occurred slightly with a strain rate of 0.001 s−1. Mechanisms of dynamic recrystallization transformed from continuous dynamic recrystallization to discontinuous dynamic recrystallization with the increase in strain when it was deformed at a temperature of 950 °C and a strain rate of 0.01 s−1. The grain size also decreased gradually due to the dynamic recrystallization, which provided an optimal forming condition for manufacturing thin-walled components with the desired microstructure and an excellent performance.

Local and global tensile deformation behavior of AA7075 sheet material at 673oK and different strain rates

The constitutive behavior of AA7075 aluminum sheet like other metallic sheet materials is highly temperature and strain rate dependent at elevated temperatures. The uniaxial tensile test is commonly employed to characterize the temperature and strain rate dependent deformation behavior. However, the traditional uniaxial tensile testing and data analysis procedure treats the gauge length of sample as a uniformly-deforming (or homogeneous) region. This may not be accurate due to early localized deformation that is initiated in the gauge region at elevated temperatures. Treating the post-necking hardening behavior of uniaxial tensile samples has been an important task to expand the effective range of true stress-true strain curves at elevated temperatures for metal and alloys. To explore this issue, uniaxial tensile tests on AA7075-F sheets (with as-fabricated temper) were conducted at 673o K and four different test speeds. The test procedure also utilized an on-line 2-D digital image correlation (DIC) system method to obtain full-field strain map from the deforming gauge region of the test specimen. Local stress-strain curves at different points along the gauge length were then calculated based on the recorded local in-plane principal stress and strain values from macroscopic force data and current cross-section of the specimen at the chosen points. In this manner, the DIC strain analysis not only enabled the determination of stress-strain response but also the determination of strain rates at specific chosen points along the gauge length. The local stress-strain curves revealed significant deviation at an earlier stage of deformation from the global (or macroscopic) stress-strain response based on the entire gauge region. To estimate the constitutive behavior at different strain rates, a correction method to traditional stress-strain curves was applied to obtain a family of stress-strain curves at different constant strain rates based on the local stress-strain curves. Additionally, the material deformation response in the stress, strain and strain rate space in the 3D Cartesian coordinate system was also constructed for tests conducted at different stretching speeds. Further, a verification test was conducted to see if the above methodology could provide an accurate estimation of local deformation behavior of AA7075 sheet. Furthermore, the above experimental method was also coupled with the Gurson-Tvergarrd-Needleman (GTN) ductile void damage model and incorporated into ABAQUS-Explicit general purpose finite element (FE) analysis code via a VUMAT material subroutine. Good agreement was obtained for both the local and global stress-strain curves between the FE test simulation and experimental stress-strain results. The proposed experimental methodology and the resulting stress-strain-strain rate behavior is believed to be applicable in describing the strain rate-dependent constitutive behavior of AA7075-F sheet metals at 673o K.

Temperature Field Variation Law of Low Exothermic Polymer Grouting Material in Repairing Void Damage of Frozen Soil Subgrade

In this study, the self‐developed grouting mold was used to study the heat release characteristics of different density polymer grouting material under different temperature conditions. The spatial distribution characteristics of the frozen soil subgrade temperature field under the effect of polymer grouting repair were analyzed. Further, the rules governing the temperature change of a frozen soil subgrade monitoring point under the effect of polymer grouting repair were studied. The heat transfer mechanism of polymer grouting material in frozen soil subgrade was revealed. The results showed that in the void region of the frozen soil subgrade, a discontinuity zone appeared in the temperature field distribution isotherm due to the effect of voids; this zone exhibited a layered radioactive distribution along the two sides of the void area. Furthermore, during the exothermic stage of the curing reaction, the temperature distribution isotherms changed from a layered radioactive distribution to a ring distribution that decreased from the inside to outside. During the natural cooling process, the peripheral temperature of the ring isotherm first decreased and a negative temperature ring‐shaped isotherm gradually formed. Finally, the upper boundary of the influence of the heat energy released by the curing reaction on the frozen soil subgrade temperature field was determined to be 30 cm, and the lower boundary was 20 cm.

Porous plasticity revisited: Macroscopic and multiscale modeling

Porous plasticity aims to model the growth and coalescence of voids leading to ductile failure. The GTN model (1984), resulting from heuristic modifications to Gurson's homogenized hollow sphere model (1977), is used in numerous publications. The Rousselier model (1981), developed in the framework of continuum thermodynamics, is apparently similar. Both models are effective in numerical calculations, but the reasons why they perform well were not investigated in details in the existing literature, as regards transition to uniaxial deformation, relations between various modes of strain localization, finite element discretization, regularization. In the present paper, we propose first to revisit both models and to compare their fundamentally different mechanical behaviors. For stress triaxiality larger than some critical value, it is shown that theoretically the GTN model cannot achieve strain localization in a plane but only pointwise localization for the ultimate mechanical state (stress tensor equal to zero). The larger the void volume fraction (void growth), the smaller the stress triaxiality critical value. Fortunately, discretization transforms the pointwise localization into volume localization and with an appropriate Cartesian finite element mesh a more or less planar sheet of integration points can be obtained. The Rousselier model can achieve strain localization in a plane at all stress triaxialities and discretization also transforms this localization into volume localization with a characteristic element size. Second, multiscale modeling of both plasticity and ductile damage (not limited to void damage) is an essential way of progress for laboratory specimen calculations. The Rousselier model can be incorporated into polycrystalline models based on crystal plasticity, with reasonable computation times provided a reduced texture with a small number of crystallographic orientations is used. It can be coupled with a new Coulomb ductile fracture model at the slip system scale and with secondary void nucleation and growth models at the grain and slip system scales, respectively. The multiscale model is applied to aluminum CT and KAHN specimens and to steel round notched specimens.

An Improved Cauer Model of IGBT Module: Inclusive Void Fraction in Solder Layer

The void in the solder layer is one of the most important aging forms of the insulated-gate bipolar transistor (IGBT) module. In this article, the influence mechanism of different void fractions on the thermal conductivity and specific heat capacity of the solder layer is studied. An improved Cauer model considering the void damage of the solder layer is established, and its model parameter extraction method is proposed. In addition, the temperature dependence of the Cauer model and its parameter is discussed in this article. In order to facilitate the experimental study of void damage in the solder layer, we customized IGBT modules with different void fractions. The influence of void morphology on the thermal properties of the solder layer is studied by the finite-element method, and the research purpose is to verify that void fraction can represent the effect of the voids on IGBT thermal characteristics. Considering the thermal resistance and thermal capacitance affected by the voids in the solder layer, their calculation methods are given in detail. Then, under different loads, the IGBT modules with different void fractions are tested. The robustness of the improved Cauer model is verified by the experimental and numerical simulation results. The results show that the improved Cauer model has higher accuracy than the traditional Cauer model.