Microstructural damage evolution under different stress states plays a critical role in the macroscopic ductile fracture of sheet metals. This study proposes a two-scale numerical framework that links microstructure informed simulations with macroscopic fracture modeling for an AA6061-T6 aluminum alloy sheet. A crystal plasticity-based representative volume element (CP-RVE) model is developed in DAMASK to simulate deformation under proportional loading paths, including simple shear, uniaxial tension, plane strain tension, and equibiaxial tension. At the macroscale, the modified Mohr-Coulomb (MMC3) ductile fracture criterion is calibrated using experimental fracture data for AA6061-T6 to establish a fracture locus over a wide range of stress states. Microscopic damage accumulation is evaluated using three slip-system-based damage criteria. The results demonstrate that the CP-RVE framework accurately reproduces the macroscopic stress-strain response and plastic anisotropy of the AA6061-T6 sheet, while microscopic analyses reveal pronounced heterogeneity in strain and damage distributions at the macroscopic fracture instant. For example, based on the accumulated shear strain-based damage criterion calibrated using the RVE response under uniaxial tension, approximately 19%, 60%, and 52% of the material points reach the fully damaged state at the macroscopic fracture strain under simple shear, uniaxial tension, and equibiaxial tension, respectively. In contrast, under plane strain tension, none of the material points reach complete damage at the macroscopic fracture instant. Overall, this work highlights the potential of CP-RVE simulations as controlled virtual experiments for investigating microstructural damage evolution and for supporting the calibration of macroscopic phenomenological ductile fracture models, thereby reducing reliance on extensive experiments.

This study presents an automated deep learning-based framework for the quantitative analysis of fracture surface microstructural defects in selective laser melting produced Ti6Al4V tensile specimens. Six sets of samples were fabricated with systematically varied laser power, scan speed, and heat treatment to isolate their effects on defect formation. A deep learning object detection model was trained on 1000 annotated scanning electron microscopy images and applied to classify and segment three defect types: Gas Pores, lack of fusion, and unmelted powder. A Python-based pipeline extracted per-defect metrics including count, area, and density. Results show that increasing scan speed by 20

In burnishing process, due to local deformation and ball rolling, material is subjected to complex stress state and different stress components are applied to the workpiece. Under these loading conditions, material enters the plastic zone and accumulation of plastic strain leads to the development of damage within the workpiece. Damage prediction in multi-stage processes is challenging. In this work, modeling of process was performed using finite element (FE) method and contact mechanics theory. Little research has been done on the mechanism of damage accumulation in burnishing, so the aim of this work is to investigate the process mechanics and damage prediction using a nonlinear model. The damage model was defined by the VUSDFLD subroutine in Abaqus software. The effect of reverse loading on damage growth and the accuracy of predicting failure onset was investigated. Deformation mechanics indicate severe changes in the stress state, which should be considered in the calibration of damage criterion. Therefore, the nonlinear model was calibrated by a new test appropriate to the loading in burnishing. According to the results, using the nonlinear criterion and choosing the damage formation threshold of-23, the critical penetration depth was predicted with an error of 4.54 %. The effect of threshold value on the moment and location of failure initiation is significant, such that its non-definition led to an error of 36.4 % in predicting the critical penetration depth. Plastic strain was used to estimate the work hardening. The variations in plastic strain along the thickness correspond to hardness distribution in workpiece.

A combined experimental-numerical framework was developed to investigate the ductile fracture behavior of AA6061-T6 aluminum alloy sheets under conventional and ultrasonic-assisted tensile loading. Fracture initiation was predicted using the stress-state-dependent Modified Mohr-Coulomb (MMC) criterion implemented in a finite element framework through a user-defined VUMAT subroutine. Two calibration strategies were assessed: a conventional quasi-static approach and a process-aware strategy that incorporated ultrasonic-assisted fracture data from four tensile configurations-uniaxial, plane strain, notched, and in-plane shear-spanning a wide range of stress triaxialities and Lode angle conditions. The conventional calibration captured quasi-static behavior but showed increasing errors under ultrasonic excitation, particularly at low triaxialities. In contrast, the process-aware calibration improved predictive accuracy across all amplitudes and loading paths, reducing fracture strain discrepancies from 14.7% to below 5.3%. Stress-state analyses revealed amplitude-dependent perturbations in stress triaxiality and the normalized Lode angle parameter, which governed the changes in ductility. The resulting fracture envelopes exhibited a non-monotonic dependence of fracture strain on vibration amplitude. Fractographic observations confirmed these trends, showing larger and deeper dimples at intermediate amplitudes and less ductile features at high amplitudes.

This study investigates the incremental forming of shallow non-axisymmetric AA6061-T6 aluminum sheet parts without the use of a peripheral blank holder. While most previous studies focus on axisymmetric geometries or constrained blank conditions, the feasibility and deformation behavior of free-edge non-axisymmetric parts remain insufficiently understood. In this work, five different single-stage and multi-stage toolpath strategies are experimentally and numerically evaluated for sheets with free-edge lengths of 6, 10, and 14 mm. The results demonstrate that non-axisymmetric parts can be successfully formed up to a height of 10 mm using multi-stage strategies without peripheral support. Among the investigated approaches, the incremental angle-increase strategy with decreasing diameter improved thickness distribution by up to 7% compared to other strategies. Distinct fracture modes were observed depending on the free-edge length and toolpath design, including circumferential corner cracking and radial edge cracking. Furthermore, analysis of in-plane strain evolution revealed a significant change in strain-path slope at the onset of fracture for larger free edges. These findings provide new insights into deformation stability and fracture mechanisms in free-edge incremental forming of non-axisymmetric geometries.

Challenges such as limited formability, high springback, and wrinkling in aluminum forming are addressed using electromagnetic forming (EMF), a high-speed technique that accelerates the workpiece for precise forming. This study investigates stepped tube production by EMF, experimentally and using Finite element simulation. A key focus is the detailed exploration of EMF for stepped tubes, resolving issues like uneven thinning and poor material flow. In this study, Aluminum 6063 tubes with a thickness of 0.95 mm were used. A coil was optimized in COMSOL by analyzing parameters such as the number of turns of the coil, wire spacing, and coil-to-workpiece distance to enhance quality. Additionally, implementing air venting channels in the die design eliminated dents and incomplete filling, enhancing production outcomes. Initial single-step tests at 4, 5, and 6 kV showed insufficient filling and excessive thinning, leading to the development of a multi-step approach. In addition, precise three-dimensional modeling with full coupling was improved simulation accuracy for complex geometries. Two-step and four-step methods overcame single-step limitations. Results confirmed that the two-step method at 4 kV and 6.5 kV achieved optimal outcomes, with a 30.67% expansion ratio and a 20% improvement in thickness distribution. An inverse analysis estimated the coefficient C in the Johnson-Cook model, enhancing material behavior predictions. These advancements address EMF challenges and offer opportunities for industries like automotive and aerospace.

Two-point incremental forming (TPIF) is a flexible sheet metal forming process, commonly divided into positive and negative configurations. In order to improve the dimensional accuracy, thickness distribution, and overall formability of conical sheet parts, this study examines the negative TPIF approach. A series of experiments were conducted by varying key process parameters including tool diameter, vertical step size, forming strategy, and lubricant type. The forming process was performed on 0.9 mm thick St12 steel sheets using a CNC milling machine equipped with a full die set and a spherical-head forming tool. According to the results, increasing the tool diameter reduced material thinning and failure risk by improving thickness distribution and increasing the minimum wall thickness from 0.24 mm to 0.5 mm. On the other hand, sharp features were better defined with smaller tool diameters. The corresponding plastic strain was decreased and the risk of tearing was reduced by using a multi-stage forming technique, which also improved strain distribution and decreased thinning. Lubricant type showed limited influence on geometric accuracy or thickness uniformity but had a noticeable effect on surface finish. Overall, this study demonstrates that tool geometry and forming strategy are critical in optimizing the performance of negative TPIF processes. The findings provide practical guidelines for improving the structural integrity and precision of incrementally formed sheet metal parts.

Plastic strain and ductile damage are two factors affecting the mechanical properties of parts processed by burnishing process. It is well known that excessive processing in burnishing leads to surface damage and defects. In this study, a numerical model has been developed to determine the loading mechanism and damage distribution in the burnishing. Ductile damage was investigated by the MMC criterion by the appropriate subroutine in the commercial code Abaqus. Fracture tests were performed including compression, uniaxial tension, notched tension and in-plane shear. In order to calibrate the MMC criterion, an inverse and combined experimental-numerical method has been used. The stress and strain state in single-stage and multi-stage burnishing has been comprehensively investigated. According to the results, the deformation is applied locally and the loading path in burnishing is highly nonlinear and non-proportional. The results indicate changes in plastic strain and stress state along the thickness of the part. The greatest amount of damage occurred at the surface of the part, while the greatest plastic strain occurred below the surface. Comparing simulation results with experimental tests indicate the accuracy of predicting surface damage and failure by the numerical model. As the penetration depth increases, larger tensile stresses are applied to the material, thus increasing the damage growth rate. According to the experimental results, surface failure (flaking) and defects were formed at a penetration depth of 0.11 mm, while the results from FE simulations predicted a critical penetration depth of 0.13 mm, with a prediction error of 18.2

The automated detection of microstructural defects in additively manufactured Ti6Al4V materials presents significant challenges due to the lack of comprehensive datasets and the variability of defect types. This study introduces a novel methodology for addressing these challenges by developing a Microstructural Defect Dataset (MDD) specifically tailored for scanning electron microscopy (SEM) images. We trained and evaluated multiple YOLOv8 models YOLOv8n, YOLOv8s, YOLOv8m, YOLOv8l, and YOLOv8x using this dataset to assess their effectiveness in detecting various defects. The principal results demonstrate that YOLOv8m achieves a balanced trade-off between precision and recall, making it suitable for reliable defect identification across diverse defect types. YOLOv8s, on the other hand, excels in efficiency and speed, particularly for detecting 'Pore' defects. The study also highlights the limitations of YOLOv8n in detecting specific defect types and the computational challenges associated with YOLOv8l and YOLOv8x. Our methodology and findings contribute to the scientific understanding of automated defect detection in additive manufacturing. The development of the MDD and the comparative evaluation of YOLOv8 models advance the state of knowledge by providing a robust framework for detecting microstructural defects. Future research should focus on expanding the dataset and exploring advanced AI techniques to enhance detection accuracy and model generalization.

One of the main limitations of 6000 series aluminum alloys in industrial forming is their low formability at ambient temperature. This study presents a novel experimental–numerical approach to enhance and characterize the formability of annealed AA6061 alloy under complex stress states using electric current. Hydraulic bulge tests were conducted on equibiaxial, circular notch, and oval notch specimens with and without electric current. To isolate athermal mechanisms, surface temperature was monitored during forming, confirming negligible Joule heating. The results showed that electric current increased equivalent plastic strain by 18.18

An accurate material model significantly improves the simulation accuracy of tube hydroforming processes. To precisely calibrate a ductile fracture criterion, it is necessary to conduct fracture experiments that encompass a broad spectrum of stress conditions. Furthermore, a more accurate calibration is achieved when applying tube geometry-based tests, which present a more exact reflection of process conditions. Comprehensive phenomenological criteria with a wide coverage of stress states have not been used in the tube hydroforming process. Moreover, the need for a comprehensive calibration process based on tube geometry has not been underlined due to the simplicity of the considered criteria. This research provides a novel environment where innovative fracture experiments with nested tubes are designed and performed in a single setup. Certain cut-outs with special geometries are designed on the outer AA6063-T6 tube, considered for fracture. The inner tube, made of ductile metal, acts as a medium to transfer hydraulic pressure to the outer tube. Iterative finite element simulation was applied to design the geometry of cut-outs on the outer tube. The modified Mohr-Coulomb criterion (MMC3) is calibrated using these fracture experiments. A comparison between the experimental and simulation results showed the efficiency of the fracture criterion calibrated by the proposed tests, where the pressure, bulge height, and tube thickness at fracture onset were predicted with average errors of less than 13%, 9%, and 3%, respectively.

Nowadays, to increase of sheet hydroforming's precision and effectiveness, new processes can be combined with it such as ultrasonic vibration. Even synchronic use of these two methods was studied in some metal forming processes such as tube hydroforming, but it has not been studied in sheet hydroforming. Therefore, the aim of this research is the experimental study of St14 sheet hydroforming with the assistance of ultrasonic vibration. For this purpose, ultrasonic vibration (with 20 kHz frequency and 4 mu m amplitude) was applied radially to the punch of a hydro-mechanical deep drawing die. Then, process parameters consisting of LDR, maximum height, forming force, safe working zone, and thickness distribution were determined and compared in four states conventional deep drawing (CDD), hydroforming deep drawing (HDD), ultrasonic vibration assistance deep drawing (UDD) and ultrasonic vibration assistance hydroforming deep drawing (UHDD). Results indicate that applying ultrasonic vibration into the sheet hydroforming process increases LDR by12.5% and the maximum height of the cups by 35% compared to conventional deep drawing, decreases forming force by 8% and develops a safe working zone. Also, it effectively reduced thickness distribution by 18% and decreased sheet thinning in critical sections by 16%. Therefore, it is possible to see the positive effects of ultrasonic vibration on sheet hydroforming process. This situation can be justified from two macroscopic (ultrasonic lubrication) and microscopic aspects (acoustic softening).

Non-rotary flat slide ball burnishing (NRFSBB) was developed as a surface finishing process. Due to the first-time utilization of non-rotary sliding contact in the ball burnishing process, a comprehensive investigation of the polishing and hardening aspects after NRFSBB was conducted. The influence of NRFSBB parameters including vertical depth, step-over, and number of passes on surface roughness and microhardness was examined. NRFSBB experiments were performed on a face-milled AA7075-T651 plate. Compared to the face-milled surface, longitudinal roughness, transverse roughness and microhardness were improved by up to 90.4

In this paper, the original and shear-modified GTN ductile fracture criteria are utilized to investigate the fracture behavior of the AA6061-T6 aluminum alloy sheet during the stretch bending process. An appropriate calibration strategy is presented to find the unknown coefficients of the fracture models. In this way, different tension tests such as uniaxial tension, plane strain, notched tension, and shear tension specimens are utilized. Results show that the shear-modified GTN model calibrated by the mentioned tension tests is able to predict the onset of fracture of the stretch bending process with a 5% error, while the original GTN model, calibrated by the uniaxial tension is unable to predict the fracture properly. Since the accuracy of fracture prediction depends on the stress state, the effects of the calibration test on onset of fracture were investigated. It is shown that using the original GTN model with a proper calibration test (plane strain tension) can achieve a good accuracy with 3.5% error in the stretch bending process. In addition, results show that any change in the friction coefficient and bending radius in the stretch bending process can lead to different fracture behavior. Several investigations are carried out to examine the evolution of damage and displacement of fractures in the stretch bending process under different forming conditions.

Non-rotational sliding ball burnishing (NRSBB) was developed as a polishing process. The effect of NRSBB parameters on longitudinal and transverse roughness (Ra || & Ra perpendicular to), and microhardness (MHV) of AA7075-T651 face-milled plate was investigated by response surface methodology. Ra || decreased by increasing the ball diameter. Ra perpendicular to increased with increasing the burnishing depth and step over. MHV was enhanced by increasing burnishing depth and passes. The optimal parameters obtained from multi-objective optimization were the ball diameter of 10 mm, burnishing depth of 0.18 mm, step over of 0.062 mm, five passes, and feed rate of 1050.3 mm/min. Compared with the face-milled surface, the optimized NRSBB improved Ra ||, Ra perpendicular to and MHV by 93.7%, 89.3% and 37.3%, respectively. The topographic parameters of Sa, Sq, Sp and Sv improved by 89.3 %, 87.5%, 76.4% and 88.9%, respectively. The microhardness distribution of the optimized sample indicated 600 mu m hardened depth.

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Today, the use of sheet hydroforming methods in the conventional deep drawing process has significantly improved the formability of the sheet. However, due to the limitations of the sheet hydroforming process, new methods can be used in combination with it, such as ultrasonic vibration–assisted forming. Many of the mechanical effects of ultrasonic vibration in the metal forming process are due to the metallurgical and structural impacts of the material. Hence, to find the cause of the observed cases, one must look at the microstructural interactions of materials. Therefore, the process of St14 sheet hydroforming with the assistance of ultrasonic vibration is investigated microstructurally in this paper. For this purpose, during the hydroforming drawing process, ultrasonic vibration was radially applied to the punch in a hydro-mechanical deep drawing die. Then, the process parameters, including thickness, equivalent strain, grain size, and rotation at a selected point of the cross-section of the sample parts, are compared in four modes of conventional deep drawing (CDD), hydroforming deep drawing (HDD), deep drawing assisted by ultrasonic vibration (UDD), and hydroforming deep drawing assisted by ultrasonic vibration (UHDD). Results showed that the application of ultrasonic vibrations in the sheet hydroforming process led to a significant reduction in thickness strain (as well as equivalent strain) in the wall of the cup, increased grain length, and reduced rotation. This implies that the positive impact of ultrasonic vibrations in the flow of materials is due to the reduction of friction and facilitates the movement of dislocations.

This research is focused on the modeling of the deformation behavior of thin austenitic stainless steel sheets to consider size effect in microscale. First, the material with two different thicknesses is heat treated to obtain different grain sizes, and then they are characterized by the uniaxial tensile tests. The experimental results show that flow stress decreases with the reduction of the sheet thickness and the increase of the grain size. The decline of the flow stress curve is associated with the decrease of the strength coefficient and increase of the hardening exponent as the plastic deformation is scaled down to the microscale. To better model the behavior of the material in the microscale, a new constitutive model is proposed based on the Swift equation to take into account the geometry and grain size effect. This model is also defined in the finite element model of the uniaxial tensile test. It is found that the flow stress curve predicted by the proposed constitutive model shifts down by the decrease of the number of grains across the thickness, which are consistent with the experimental results. In addition, the finite element model with the proposed constitutive model predicts accurately the deformation load in the uniaxial tensile tests. It can be concluded that the proposed constitutive model can provide a good description of the flow stress by considering the interactive effect of specimen and grain sizes and can be used in the modeling of material behavior in microforming processes.

Recent studies have proven the possibility of polymer sheet forming by incremental sheet forming (ISF) process, while there are limited studies on ISF of polymer matrix composites. Fiber-reinforced polymers (FRP) are significantly useful in industries due to their unique properties. In the current study, owing to the merits of ISF and the wide applicability of FRP, single point incremental forming (SPIF) of polyamide 6 (PA6) sheets reinforced by glass fibers (GF) is taken into account at various forming temperatures. In this regard, a fixture equipped with a ceramic infrared heating element was designed. The effect of some important parameters such as the volume fraction and orientation of fibers and the forming temperature on the formability, the thickness distribution, and the dimensional accuracy of PA6 and PA6/GF sheets is investigated. According to the results, an improvement in the formability of the composite sheet can be obtained using SPIF by increasing the forming temperature and decreasing the volume fraction of fibers. The formability of the composite sheet with the fiber orientation of [0/90] is far less than the one with unidirectional fibers. In the most of the successfully formed samples, the transverse compaction and the fracture of fibers at the part bottom, the buckling of fibers at the edge of the backing plate, and the draw-in of the sheet along the main direction of fibers can be detected. The thinning of the composite sheet is most affected by the volume fraction and orientation of fibers, while the forming temperature has the least effect. Moreover, the feasibility of SPIF of a circular flange with a wall angle of 90° from the composite sheet is assessed at elevated temperature.

Multi-layer sheets with combined properties such as a high strength-to-weight ratio, good corrosion resistance, and desirable electrical and thermal conductivity are employed in various application fields. In this research, the deformation behavior and fracture of a bimetal sheet during the single point incremental forming process (SPIF) are investigated. The AA1050 aluminum and 10100 copper sheets are utilized to fabricate the laminated sheet through the explosive welding process. Various geometries are designed to induce different stress and strain states through the SPIF of the two-layer sheets. To describe fracture phenomena, the Xue-Wierzbicki damage criterion incorporating the Hill48 anisotropic yield model is implemented in the Abaqus/Explicit finite element (FE) code via user subroutine VUMAT. The SPIF experiments are also carried out to validate predictions from the FE model considering fracture depths of different geometries and sheet thinning. The effect of layer arrangement is also studied, and the comparison between the fracture depths of SPIF experiments with predicted ones shows an average discrepancy of 6.5% for both layer arrangements of bimetal. Using the element deletion technique, the fracture location of SPIF parts was obtained through the FE simulations, which was in line with the real observations. The stress states of the localized deformation field in SPIF of the two-layer sheets are analyzed in the space of the stress triaxiality and Lode angle parameter. The strain states are also investigated in the forming limit diagram space, which indicated highly nonlinear loading conditions in this process. Using the damage criterion, the participation of influential factors at the fracture initiation of SPIF parts is discussed. It is found that regardless of the layers arrangement of the laminated sheets, initiation and propagation of the cracks take place from the outer layer. Experimental results in agreement with FE predictions revealed that various geometries of the bimetal sheets would have higher fracture depths when the aluminum layer is the outer layer and the forming tool contacts the inner copper layer. In addition to showing excellent predictions, the fracture forming limit curve (FFLC) of the bimetal sheet in SPIF is compared to that in the hemispherical punch stretching process. The comparison demonstrates the higher level of the calculated fracture strains in the SPIF process than in the stretching tests. It highlights the positive role of nonlinear loading versus a proportional loading condition in improving formability.