This study introduces a novel flowformability test aimed at replicating the complex loading conditions of industrial flowforming processes—alternating stress triaxiality, large plastic strains, and high strain rates. A novel Conical Flowformability Test (CFT) configuration was selected for experimental validation due to its ability to achieve a high theoretical thickness reduction while respecting machine constraints. Experiments conducted on AA6061 in O-temper and W+3h states demonstrated substantial thickness reductions. Comparison between the numerical simulations using the software FORGE® and the experimental results is satisfactory despite certain unquantifiable experimental defects such as fish scales and material build-up. The current study paves way to establish a robust framework for assessing material flowformability and damage evolution under realistic process conditions.

Spinning processes are incremental sheet forming (ISF) operations that require computationally expensive numerical simulations due to the large number of increments required and complex tool-workpiece contact interactions. Similarity theory has demonstrated its applicability to spinning process modeling and, when combined with mass scaling, shows potential for increasing computational efficiency. This potential is investigated in this work through a metal spinning setup. A model of the process is developed using two process kinematics approaches: the classical one as used in experiments, and a modified version where the roller follows an enforced helical path while the mandrel remains fully constrained. Comparison of global and local outputs demonstrates very similar predictions for both kinematics. Analysis of mass scaled models using the modified kinematics reveals that higher scaling factors lead to interference from inertia effects and deteriorated contact treatment due to increased time increments. The choice of mass scaling factor depends on the trade-off between the computational time and the desired model accuracy. For the present spinning configuration, mass scaled similar models show no clear improvement in predicting local variables compared to mass scaled full-size models at equivalent computational times.

Metallic naval structures can undergo progressive damage from external incidents, affecting their ability to withstand subsequent impacts. Ductile damage is known to be sensitive to the stress state according to two scalars, the stress triaxiality ratio n and the Lode parameter L, that determine respectively the loading type applied and the position of the medium principal stress according to maximum and minimum ones. Ductile damage is studied experimentally with specific geometries targeting specific (n; L) values. Bulge Explosion Tests (BETs) are used for naval structures qualification to impact. Thick plates undergo various loading conditions, including an equi-biaxial tensile loading condition (0.66; 1). One way of obtaining this stress state is by using a punch test, where a fixed disk is punched up to fracture. Due to friction, the loading condition is not guaranteed in the rupture area. It is important to include such stress state for damage models calibration, which should be able to predict the ductile failure initiation under such conditions. This work focuses on both development and methodology used for a mini-punch system dedicated to damage parameters calibration, using DIC (Digital Image Correlation) and numerical simulations with various (n; L) conditions.

The thermal expansion behavior of polymers is a crucial property for manufacturing photovoltaic (PV) modules. The thermal expansion mismatch between the different module components induces residual stresses in the structure after manufacturing. Some of them are located at the interface between materials, leading to delamination and reliability issues during the PV module lifetime. For tandem applications, the thermal expansion mismatch is also an issue since it leads to the separation between the bottom and top cells. In this article, the thermal expansion behavior of a thermoplastic polyolefin (TPO) encapsulant used in the PV industry is assessed by stereo digital image correlation. This contactless method measures the thermal expansion in the two directions of the polymer thin film. The method is accurate enough to capture transition phases of the material, namely the crystallites fusion and formation. The thermal expansion behavior of the TPO thin film is shown to be anisotropic and dependent on its thermal history. The material contracts when heated, both after manufacturing and after aging; this has not yet been investigated. The aging temperature has an influence on the thermal contraction temperature but does not erase the shrinking behavior. The thermal expansion behavior is explained by a microstructural approach. The microstructure is investigated by differential scanning calorimetry. After crystallites melting, the molecular mobility and residual internal stresses account for the observed shrinking behavior. This behavior may affect the reliability of PV modules through delamination, cells cracks, or separation of the top and bottom cells.

A microstructural analysis of Inconel 718 tube flow forming is presented. The grain fragmentation analysis shows that the increase of the number of reduction passes allows a more homogenous distribution of strain which may explain the higher ductility observed when the number of reduction passes increases. Additionally, recrystallized grains and δ phase volume fraction increase were observed. This observation indicates a temperature increase and a very high increase of the δ phase precipitation kinetics.

In this work the latest developments on the damage to fracture transition modeling framework of FORGE® are presented. In [8] & [9] the CIPFAR algorithm (Crack Initiation and propagation using the Phase Field and Adaptive Remeshing) was introduced, leading to a shift in the mesh management paradigm to introduce real cracks from damage fields and for ductile forming simulations. In this work we review the generalized framework enabling to: (1) Simulate damage initiation and propagation as a field state variable following any user-specified material law. This state variable is then used within a Phase-Field approach that serves as a proxy variable to identify the crack location within the continuous mechanics framework. (2) Introduce actual crack discontinuities in the finite-elements mesh by intersection of the phase-field’s gradient with the current mesh. Coupled with an automatic mesh adaptation technique this approach creates a robust framework for complex forming scenarios involving fracture. Further improvements are also introduced in this work: (a) The phase-field framework introduced new numerical parameters, such as a characteristic crack length, that can complexity the model adjustment and its industrial use, here we propose an automated approach to reduce the numerical adjustments. (b) As the crack insertion lays on top of the phase-field gradient computation, and the latter on a field recovery strategy, we also present a tensor filtering strategy enabling a better description of the phase-field gradient required for crack intersection. (c) An alternative automatic isotropic remeshing strategy is also introduced.

Spinning processes are incremental forming processes whose numerical modeling involves several difficulties related to the high rotational speed of the workpiece and very localized roller-workpiece contact area. Based on a shear spinning model, some major modeling options in Abaqus® finite element software are investigated, after a prior comparison of the simulation results from Abaqus® and Forge®. Conclusions are drawn regarding results accuracy and computational cost. The relevance of the tested options is thereafter discussed.

Numerical simulation of ductile fracture in the field of metal forming represents one of the most challenging tasks. Throughout the chain of manufacturing processes, the accurate prediction of the crack surfaces is essential for the quality of the final products. The application of a crack initiation and propagation algorithm known as CIPFAR is presented in order to model the complex ductile fracture processes. In addition, a phase field approach is coupled with a ductile damage criterion to simulate the transition from damage to fracture. The self-contact between crack faces is also modeled through the penalization method in order to prevent the penetration of crack faces. The presented algorithm serves as an efficient computational tool for the industrial purposes in terms of the robustness and quality of the obtained results. Comparisons are carried out with the classical element deletion method in order to show the ability of the new algorithm to tackle the issues of mesh dependency and volume loss.

The following study aims in describing the impact of the architecture of the photovoltaic (PV) module and lamination recipe on the thermal exchange between the laminator and the PV module for different configurations. First, the PV module temperature evolution was measured during the lamination process, using temperature sensors. These temperature sensors were placed at different positions in the PV module to study the temperature gradient in the thickness and the temperature side effects. Second, data were fitted using an analytical model, developed for each lamination case to calculate the thermal exchange coefficient in double side heating plate and cooling press. Finally, the resultant coefficient was implemented numerically into a 3-D finite element model. Results reveal a correlation between experimental, analytical, and numerical temperature profiles. Experimental curves show that the corner of the PV module heats and cools down faster than the center, due to the thermal exchange between the edge of the PV module and the air in the chamber. A temperature gradient in the thickness was mainly observed in the first step of lamination (membrane/press). Numerically, we found that this temperature gradient depends on the presence of air trapped around the thermocouple, which influences the heat transfer between the layers of the PV module. In vacuum/membrane press, the heat transfer coefficient has been defined numerically due to the asymmetrical loading. This coefficient is strongly affected by the lamination recipe and the laminator configuration.

A novel flowformability test is under development at CEMEF in order to be able to predict damage at large strains under complex loading conditions corresponding to tube flowforming. The design of this test relies on 3D numerical simulations performed with the finite element software Forge® 3.1 Nxt. Such simulations, using classical implicit updated Lagrangian formulations, are costly because of the very small-time step and the fine mesh required to describe accurately the local and evolving contact of the tube with the roller (s). The aim of this paper is to study the relevance and the influence of the use of symmetry conditions in the modeling accuracy of this flowformability test.

Flow forming is an incremental sheet forming (ISF) process during which a sheet metal is compressed and stretched multiple times by means of one or multiple rotating roller tools. The local tool-workpiece contact zone evolves during the entire process. The necking phenomenon, which corresponds to an uncontrolled thinning of the part wall, is introduced. This phenomenon represents a major issue for ISF processes. A review of the state-of-the-art about ISF processes shows that most studies do not consider the loading path complexity when choosing the mechanical characterization test and its associated constitutive model. Besides, the prediction of necking occurring during sheet flow forming is poorly studied in the literature. In this paper, a finite element analysis (FEA) using the FORGE® software enables a detailed understanding of the loading path (strain and stress states) prevailing during the flow forming operation. Based on the peculiarities of this loading path, different mechanical tests associated with adequate constitutive models are chosen to characterize the material behavior. The ability of each constitutive model used within the FE approach to predict necking is then assessed. Results show that the best prediction of a geometry exhibiting necking issues is obtained with the cyclic in-plane torsion test (ITT) associated with its calibrated isotropic – kinematic hardening model. These results suggest that the behavior characterization under cyclic shear loadings is relevant. Using a simple tensile test with associated power-law provides a faster and conservative necking prediction.

Incremental forming processes can be used to produce thin products (tubes or sheets)[1]. Very high deformation of the material can be reached taking advantage of the local and cyclic loading of the material. In this study we will focus on backward flow forming of aluminum tubes. In this process, tube thickness is reduced by the combined action of a rotating mandrel that imposes the inner radius and 3 rollers that decrease progressively the tube thickness. An experimental campaign is conducted on a laboratory device to study the influence reduction rate. The corresponding configurations are simulated to understand the mechanical loading path. The material characterization is presented to focus on the influence of the chosen behavior law on flow forming simulation results. Different damage criteria coming from the literature are studied to evaluate their capability to predict fracture and to compare the amount of damage reached for each process configurations. Even if none of them is able to predict accurately damaging configurations, the classical Cockroft and Latham seems to be the only capable to reflect the hierarchisation of configurations.

In this paper, a general numerical framework for the modeling of ductile fracture in 3D meshes is introduced. The strategy is inspired from the phase field model and adaptive remeshing tools. The phase field model was introduced as a continuous model for predicting the initiation and propagation of cracks in materials. However, the model has a limitation on the choice of the characteristic length scale that controls the width of the cracked region. This work contributes to the full modeling of transition between the continuous damage using the phase field model to the discontinuous crack initiation and propagation within a unified numerical framework called CIPFAR. The contributions of the work include: (i). identification of the crack surface on arbitrary mesh topologies; (ii). intersection by a Sequence Agnostic Partitioning strategy which is introduced to adapt the mesh to the computed crack surface; (iii). a nodal duplication by virtual non-manifold patch repair to open the mesh. Combining all the mentioned algorithms with adaptive remeshing allows modeling the initiation and propagation of cracks in materials efficiently. Different numerical examples are presented to prove the ability of the developed algorithm to model ductile fracture cases without the need to predefine the crack initiation region.

Flow forming is an incremental forming process during which a roller tool deforms a rotating sheet metal by applying a force which is local and evolving during the entire process. The finite element software FORGE® is used in order to model this process. The local tool-workpiece contact conditions and the high rotation speed make the modelling of this process difficult with high computation time. It is, therefore, necessary to develop optimization strategies aiming to reduce the computation time whilst maintaining a sufficient level of results accuracy. A first configuration optimization method consists of reducing the geometry of the initial blank and using symmetry planes. The final reduced geometry obtainable is 36° wide. This method is then associated with a second one which consists of reducing the number of calculation time steps during the entire process. The calculation time steps removed are those occurring when the roller tool is not in contact with the deformable sheet metal anymore. The two combined methods give the ability to drastically reduce the computation time compared to the reference case. In addition, the global and local results of the reference case are mostly conserved when applying the configuration optimization methods.

OBJECTIVE:Thermocycling is widely used to age dental composites but with very different results from one study to another, even with apparent similar conditions. This study aims at understanding better the relative damaging speed of matrix and fillers, based on theoretical models. METHODS:Eight formulations of an experimental dental material were produced. The same organic matrix was used and silanated barium glass particles were added as fillers with different filler ratios. Samples were thermocycled up to 10 000 cycles. Three-point bending tests were carried out at different steps. The yield stress was measured among other mechanical properties. RESULTS:Composite properties were degraded by thermocycling. The decrease was slight during the first 5 000 cycles whereas it decreased significantly after 10 000 cycles. The Turcsányi model asserts that the interface yield stress is slightly affected in the first 5 000 cycles and then falls down, while the decrease of matrix yield stress is linear. SIGNIFICANCE:Each component of a composite does not age at the same rate. First, the matrix acts as a protector until the water finds its way to the interphase. The filler silanization treatment is highly sensitive to hydrolysis and is damaged rapidly from that moment. Numerical simulations and surface observations confirmed that cracks appear to propagate in the neighbourhood of the interface but not directly within it.

The goal of this work is to predict ductile failure of pipe-ring notched AISI 316L specimens, where notches mimic the geometry of corrosion defects. Uncoupled damage models are used to that end. The Johnson-Cook and LouHuh criteria are calibrated. The uncoupled damage models are calibrated using experimental results from testing pipe-ring notched specimens. Calibration was achieved using a hybrid experimental-numerical approach. Six notch shapes are studied. Experimental matrices are designed to determine these shapes, and the pipe-ring notched specimen is inspired from the literature. Calibration of the uncoupled damage models require a ductile crack initiation indicator. The first indicator was based on the derivative curves of the force versus the connectors displacement curve. The second was based on the raw images of the gage section. The third was based on a percentage of the connectors displacement at fracture. Results show that ductile fracture depends on the Lode paramater. As a consequence, the Lou-Huh criterion is more effective at predicting ductile fracture than the Johnson-Cook criterion.

It has been experimentally observed that the Zn–Cu–Ti zinc alloy shows a strong influence of strain rate and temperature on its plastic behavior. A significant change in the material response is seen with relatively small strain rate variations or temperature. In this work, these effects are addressed through the Cazacu–Plunket–Barlat 2006 (CPB-2006) yield criterion and the Johnson–Cook hardening law. The tests were carried out over the three main directions: rolling, diagonal, and transversal. Three strain rate conditions (0.002, 0.02, and 0.2 s−1) and three temperatures (20, 60, and 80 °C) were tested. Although the experimental results exhibit a significant influence of the strain rate and temperature on stress–strain curves for all tested directions, such two variables do not practically affect the Lankford coefficients. The proposed model calibration procedure is found to describe the material responses properly under the studied conditions.

Microscopic digital volume correlation (DVC) and finite element precoalescence strain evaluations are compared for two nodular cast iron specimens. Displacement fields from \textit{in-situ} 3D synchrotron laminography images are obtained by DVC. Subsequently the microstructure is explicitely meshed from the images considering nodules as voids. Boundary conditions are applied from the DVC measurement. Image segmentation-related uncertainties are taken into account and observed to be negligible with respect to the differences between strain levels. Macroscopic as well as local strain levels in coalescing ligaments between voids nucleated at large graphite nodules are compared. Macroscopic strain levels are consistently predicted. A very good agreement is observed for one of the specimens, while the strain levels for the second specimen presents some discrepancies. Limitations of the modeling and numerical framework are discussed in light of these differences. A discussion of the use of strain as coalescence indicator is initiated.

It has been shown that temperature cycles on airless bodies of our Solar System can cause damaging of surface materials. Nevertheless, propagation mechanisms in the case of space objects are still poorly understood. Present work combines a thermoelasticity model together with linear elastic fracture mechanics theory to predict fracture propagation in the presence of thermal gradients generated by diurnal temperature cycling and under conditions similar to those existing on the asteroid Bennu. The crack direction is computed using the maximal strain energy release rate criterion, which is implemented using finite elements and the so-called Gθ method (Uribe-Suárez et al. 2020. Eng. Fracture Mech. 227:106918). Using the implemented methodology, crack propagation direction for an initial crack tip in different positions and for different orientations is computed. It is found that cracks preferentially propagate in the North to South (N-S), in the North-East to South-West (NE-SW) and in the North-West to South-East (NW-SE) directions. Finally, thermal fatigue analysis was performed in order to estimate the crack growth rate. Computed value is in good agreement with available experimental evidence.

In this paper, a phase field model of ductile fracture is described within the framework of large plastic strains. Most results dealing with phase field modeling of ductile fracture are carried out on a fixed mesh, which requires a fine mesh throughout all the computation. The aim of this paper is to introduce an adaptive isotropic remeshing strategy coupled with a phase field model of ductile fracture to achieve accurate results with a major decrease in computational time. A mixed velocity/pressure finite element formulation is used for the solution of mechanical fields. The plastic strain field needs to be transferred to the new mesh after each remeshing operation. This field transfer requires the use of a suitable remeshing-transfer operator. Different field transfer operators are tested and results are reported. In order to reduce the numerical diffusion associated with the field transfer operation, a volume quality based metric has been introduced. This paper presents different numerical examples with both qualitative and quantitative analyses in order to show the ability of the developed strategy in predicting crack evolution in ductile materials. The proposed framework is also able to predict crack paths in highly ductile materials while benefiting from space-adaptivity.