A formability index for the deep drawing of stainless steel rectangular cups

This study was the use of the finite element method in the deep drawing process of a rectangular shell cup. The aim was to analyse the equivalent strain in the workpiece and to find out what happened to the disc blank sheet before the forming by stamping. The rectangular shell cup was 24x30x20 mm. and made of 2mm.thick SUS 403 and SUS 304 stainless steel. There were 3 types of blank sheets: 1) square sheet 2) 45 degree angled edge cutting sheet 3) circular sheet. It was found out that the drawing up with the use of 3 types of blank sheet made of SUS 304 stainless steel had no risk in the workpiece. For the stamping of the rectangular shell that used a square sheet made of SUS 403 stainless steel, it was found out that there was no risk in the work piece, but with the use of 45 degree angled edge cutting sheet or round sheet, the work piece had a risk to be damaged. Keywords: rectangular shell, Finite element 1. INTRODUCTION Deep drawing is very important to component manufacturing of parts of a product in industries. The problem of the rectangular shell cup deep drawing process was the equal amount of flow in each side, resulting in making mould in an actual production process. Therefore, finite element process plays a role in analyzing the ability of a rectangular shell deep drawing process and it well known that using steel sheet in deep drawing process requires an awareness of the factors that have an effect with finished workpieces to prevent the damage that may happen with workpieces during the deep drawing process There are the factors or variable that have an influence on ability in drawing. During the deep drawing, the punch will be stamped on the blank sheet through the die opening. This process will make the bending and unbending in the die. The metal between the punch will have tensile stress along the line of the punch and the hoop compression stress. The metal on the shell wall will receive axial tension. At the bottom of the shell the metal will have tensile stress on both axial lines. This stress has an effect to the force in drawing and damage that will be

The main objective of the present work is to study the effect of different localisation criteria and yield criteria in predicting the forming limit diagram (FLD) of dual phase (DP) 590 steel sheets. DP590 steel is used in automotive applications for structural and safety parts such as cross members, longitudinal beams, B-pillar reinforcements and bumper reinforcements. Limit dome height (LDH) tests were performed for DP590 steel sheets and experimental FLD is plotted. Tensile tests and plastic strain ratio ‘r’ tests were performed at different rolling directions to evaluate the mechanical properties The evaluated mechanical properties were used in finite element (FE) simulations to predict the FLD of DP590 steel sheet. Three material models namely Transversely anisotropic elastic plastic, 3 parameter Barlat yield law and Hill 3 R which includes diverse yield criteria Hill 48, Barlat 89 and Hill 3 R, respectively, were used in FE analysis. Three different localisation criteria namely equivalent plastic strain criterion, thickness criterion and localisation criterion based on true strain gradient were used to predict the FLD of DP590 steel sheets. It was found that predicted FLD is close to experimental FLD when localisation criterion proposed, based on true strain gradient and Hill 48 yield criterion is used.

Cathodic protection (CP) anode bed grounding resistance calculating formulae, given by CP standards, are reviewed firstly. Underground assumptions and limitations of these grounding calculating formulae are analyzed, which means formula method may encounter problems when designing anode beds in high soil resistivity area. Based on finite element analysis (FEA) method, a new grounding resistance calculation method is suggested, which is can be treated as more suitable and flexible for anode bed grounding resistance calculation in high soil resistivity condition. The main steps of FEA method, geometric model building, meshing, boundary condition and solver setting, and grounding resistance calculating according to Ohmic law, are clearly presented. In order to introduce the FEA method in detail, a realistic anode bed design program for Northwestern China area, where soil resistivity is always very high, is demonstrated. Based field soil resistivity survey data by Wenner 4-pin method, the candidate anode bed site, named Station A, is regarded as optimal site, and Barnes’ soil layer analysis method is used to predict soil resistivity distribution in depth direction. Both formula method and FEA method are used to calculate grounding resistance. The following comparison results show that formulae from COR-GS-023, GB21448-2008, РД 153-39.4-039-99 standards and FEA method give out almost the same grounding resistance results under the assumption of uniform soil resistivity, which also, from another angle, verifies the correctness of FEA method. But for FEA method, designers can include realistic soil resistivity distribution function and any anode rod layout plan in calculation model. So, FEA method can be treated as a more flexible tool to calculate CP anode bed grounding resistance.

Based on finite element simulation to study the mode of double-column gantry milling machine. First, the establishment of three-dimensional model of double-column gantry milling machine, and then simplified the three-dimensional model, took the simplified model into Abaqus simulation software. Second, completed gradually of material properties, analysis step, grid points, surface definition, definition of the boundary conditions and loads, submitted to the task. finally, gained the first 10 natural frequencies and mode shapes of double-column gantry milling machine. while using Coinv DASP V10, has been testing the first 10 natural frequencies and mode shapes of the system structure, finite element analysis results did contrast with the experimental data, error of the finite element analysis results within 15% are credible. shows that the finite element simulation results are credible. To provide an economically viable design of large-scale equipment. and provided guidance for the experiment.

A process of modeling and reconstructing human head injuries involved in traffic crashes based on ABAQUS/Explicit is presented in this paper. A high-fidelity finite element (FE) model previously developed by the authors is employed to simulate a real accident case that led to head injury. The most probable head impact position informed by CT images is used for the FE modeling and simulation since the head impact position is critical for accident reconstruction and future analysis of accidents that involve human head injuries. Critical von Mises stress on the skull surface of the head model is chosen as the evaluation criterion for the head injury and FE simulations on 60 cases with various human head-concrete ground impact conditions (impact speeds and angles) were run to obtain those stress values. The FE simulation results are compared with the CT images to determine the minimum speed that will cause skull fracture and the corresponding contact angle at that speed. Our study shows that the minimum speed that would cause skull fracture is 3.5 m/s when the contact angle between the occipital position of the injured head and the ground is about 30°. Effects of the impact speed and the contact angle on the maximum von Mises stress of the head model are revealed from the simulations. The method presented in this paper will help forensic pathologists to examine the head impact injuries and find out the real reasons that lead to those injuries.

To predict the ductile fracture of a magnesium alloy sheet when using rotational incremental forming, a combined kinematic and isotropic hardening law is implemented and evaluated from the histories of the ductile fracture value (I) using a finite element analysis. Here, the criterion for a ductile fracture, as developed by Oyane (J. Mech. Work. Technol., 1980, vol. 4, pp. 65–81), is applied via a user material based on a finite element analysis. To simulate the effect of the large amount of heat generation at elements in the contact area due to the friction energy of the rotational tool-specimen interface on the equivalent stress-strain evolution in incremental forming, the Johnson–Cook (JC) model was applied and the results compared with equivalent stress-strain curves obtained from tensile tests at elevated temperatures. The finite element (FE) simulation results for a ductile fracture were compared with the experimental results for a (80 mm × 80 mm × 25 mm) square shape with a 45 and 60 deg wall angle, respectively, and a (80 mm × 80 mm × 20 mm) square shape with a 70 deg wall angle. The trends of the FE simulation results agreed quite well with the experimental results. Finally, the effects of the process parameters, i.e., the tool down-step and tool radius, on the ductile fracture value and FLC at fracture (FLCF) were also investigated using the FE simulation results.

Forming limit diagram (FLD) is one of the formability criteria which is a plot of major strain versus minor strain. In the present study, Gurson-Tvergaard-Needleman (GTN) model is used for FLD prediction of aluminum alloy 6061. Whereas correct selection of GTN parameters’ is effective in the accuracy of this model, anti-inference method and numerical simulation of the uniaxial tensile test is used for identification of GTN parameters. Proper parameters of GTN model is imported to the finite element analysis of Nakazima test for FLD prediction. Whereas FLD is dependent on forming history and strain path, forming limit stress diagram (FLSD) based on the GTN damage model is also used for forming limit prediction in the numerical method. Numerical results for FLD, FLSD and punch’s load-displacement are compared with experimental results. Results show that there is a good agreement between the numerical and experimental results. The main drawback of numerical results for prediction of the right-hand side of FLD which was concluded in other researchers’ studies was solved in the present study by using GTN damage model.

Pulsed laser forming is a non-contact thermal forming process, where sheet metal gets plastically deformed by thermal residual stresses induced by controlled discontinuous laser irradiations. The temperature and deformation fields have been determined using finite element analysis under different processing conditions. Two types of pulsed laser forming processes, i.e., overlapped and discrete spot forming have been identified depending on the combinations of process parameters. Bending angle is found to increase with the degree of overlap and decrease with the increase of gap in case of the two types of spot forming processes. A comparative study between pulsed and continuous laser forming has also been performed using both finite element simulations and experiments. Bending angle in case of discrete spot pulsed laser forming is found to be more compared to the continuous laser forming. The results of finite element simulations have been found to be in good agreement with the experimental results.

Among the failure modes which can occur in tube hydroforming such as wrinkling, bursting or buckling, the bursting by local instability under excessive tensile stresses is irrecoverable phenomenon. Thus, the accurate prediction of bursting condition plays an important role in producing the successfully hydroformed part without any defects. As the classical forming limit criteria, strain-based forming limit diagram (FLD) has widely used to predict the failure in sheet metal forming. However, it is known that the FLD is extremely dependant on strain path throughout the forming process. Furthermore, The application of FLD to hydroforming process, where strain path is no longer linear throughout forming process, may lead to misunderstanding for fracture initiation. In this work, stress-based forming limit diagram (FLSD), which is strain path-independent and more general, was applied to prediction of forming limit in tube hydroforming. Combined with the analytical FLSD determined from plastic instability theory, finite element analyses were carried out to find out the state of stresses during hydroforming operation, and then FLSD is utilized as forming limit criterion. In addition, the approach is verified by a series of bulge tests in view of bursting pressure and shows a good agreement. Consequently, it is shown that the approach proposed in this paper will provide a feasible method to satisfy the increasing practical demands for judging the forming severity in hydroforming processes.

Numerical and experimental investigations of forming limit diagrams in metal sheets

There has been a growing interest in recent years in the assessment of suitable vial/stopper combinations for storage and shipment of frozen drug products. Considering that the glass transition temperature (Tg) of butyl rubber stoppers used in container closure systems (CCSs) is between -55 °C to -65 °C, a storage or shipment temperature of a frozen product below the Tg of the rubber stopper may require special attention because below the Tg the rubber becomes more plastic like and loses its elastic (sealing) characteristics. Thus, they risk not maintaining container closure integrity (CCI). Given that the rubber regains its elastic properties and reseals after rewarming to ambient temperature, leaks during frozen temperature storage and transportation are transient and the CCI methods used at room temperature conditions are unable to confirm CCI in the frozen state. Hence, several experimental methods have been developed in recent years in order to evaluate CCI at low temperatures. Finite element (FE) simulations were applied in order to investigate the sealing behaviour of rubber stoppers for the drug product CCS under frozen storage conditions. FE analysis can help in reducing the experimental design space and thus the number of measurements needed, as they can be used as an add-on to experimental testing. Several scenarios have been simulated including the effect of thermal history, rubber type, storage time, worst-case CCS geometric tolerances, and capping pressure. The results of these calculations have been validated with experimental data derived from laboratory experiments (CCI at low temperatures), and a concept for tightness has been developed. It has been concluded that FE simulations have the potential to become a powerful predictive tool toward a better understanding of the influence of cold storage on the rubber sealing properties (and hence on CCI) when dealing with frozen drug products.LAY ABSTRACT: The growing interest in the assessment of suitable vial/stopper combinations for storage and shipment of frozen drug products has led to the development of a number of experimental methods to evaluate container closure integrity at low temperatures. The application of finite element simulations could aid in the investigation of the sealing behaviour of rubber stoppers for drug product container closure systems under frozen storage conditions by simplifying the experimental design space and the number of experimental measurements needed. In this work several scenarios have been simulated including the effect of thermal history, rubber type, storage time, worst-case container closure system geometric tolerances, and capping pressure. The results have been further validated with experimental data derived from laboratory experiments and a concept for tightness was developed. In conclusion, finite element simulations have shown the potential to become a powerful predictive tool toward a better understanding of the influence of cold storage on the rubber sealing properties (and hence on container closure integrity) when dealing with frozen drug products.

The mechanical behavior of aqueduct structures exhibits highly complex characteristics during prestress tensioning, making it difficult for the traditional double-control method to accurately predict and real-time control the key stresses. To improve the construction safety of prestressed tensioning and the prediction accuracy of structural prestress responses, this study develops a rapid structural mechanical property prediction method based on machine learning. Taking prestressed aqueducts as the research object, a system of “finite element simulation—sample generation—machine learning prediction” is established. Firstly, multiple groups of tensioning parameter combinations are designed via Latin hypercube sampling, and the stress responses are obtained through finite element analysis to form a high-quality training sample library. Subsequently, critical structural features are extracted based on mesh reconstruction, and stress prediction models are established using the K-Nearest Neighbors (KNN) and Random Forest algorithms respectively; the prediction performance of both models is compared and validated against finite element simulation results. Furthermore, the prediction outputs of the optimal machine learning model were used to analyze the stress distribution and potential stress concentration issues of the structure during the tensioning process. The comparative analysis results indicate that the Random Forest model performs best in terms of stress prediction accuracy and stability, and its prediction results are highly consistent with those of the finite element method. Compared with traditional finite element condition analysis, the machine learning model can complete multi-condition stress prediction in a shorter time. Leveraging its high-efficiency prediction capability, local high-stress areas of the structure in the tensioning construction scheme can be identified, thereby providing effective optimization schemes to improve the stress distribution. The mechanical response prediction method for the prestress tensioning process of aqueducts, with machine learning as the core, constructed in this paper realizes the rapid and reliable prediction of key stresses throughout the entire prestress tensioning process. This method can be applied to assist in optimizing tensioning construction schemes and construction monitoring, providing a practical technical solution for safety control of aqueduct structures during the prestress construction stage.

This study clarified the effects of the chosen hardening model, through-thickness normal stress, and non-linear strain path on the precision of forming limit diagram (FLD). The Marciniak-Kuczynski (M-K) instability theory was employed to calculate the FLD of AA5754-O based on the different hardening models. Swift, Voce, modified Voce, Kim-Tuan, and modified Kim-Tuan hardening models were adopted to predict the forming limits, and their constant parameters were presented. Predicted FLDs indicate that modified Kim-Tuan has a better agreement with experimental data than other models. After that the influences of through-thickness normal stress on the forming limit diagram were examined. The three-dimensional stress state was converted to plane-stress condition according to the assumption that hydrostatic stress is ineffective on the plastic deformation. The results show that formability improves when normal stress increases. However, the effect of the normal stress on FLD for various hardening models is different. Due to the complexity of sheet metal forming, the strain path of the material may change during the deformation process. The results indicated that strain path has a significant effect on the FLD, and the path dependence of the forming limit stress diagram (FLSD) will be examined in detail. Finally, the forming limits were computed to analyze the effect of the normal stress on the non-linear loading path deformation. It was observed that by increasing the amount of pre-strain, the effect of the normal stress on the formability will diminish. Moreover, results showed that normal stress will affect the path dependence of the FLSD.

Three-dimensional macro-mechanical finite element model for machining of unidirectional-fiber reinforced polymer composites

The Forming limit diagram (FLD), also known as a forming limit curves (FLC), is generally used in metal forming for predicting forming behavior of metals. The purpose of the study is to clarify the difference among the FLC of tubes with initial wall-thickness difference under tension-compression strain states using finite element (FE) simulation of tube hydroforming (THF) and different instability criteria. Firstly, geometrical models for SUS304 stainless steel tubes with initial wall-thickness differences were built by introducing an index ‘wall-thickness deviation rate’. Secondly, forced-end hydro-bugling of the tubes was modeled and the forming process was simulated by using the commercial finite element (FE) code ABAQUS/Explicit 6.10. Afterwards, the limiting strains of the material in the hydro-bugling process were calculated based on the simulated resultant data and three instability criteria--strain change criterion, strain rate change criterion and strain path change criterion, respectively. Finally, the FLD for the tubes was established and the effect of wall-thickness deviation rate on the FLD was analyzed and the differences among the FLC based on the three instability criteria were compared. The results showed that the FLC are observed to shift in the major–minor strain coordinate system due to the initial non-uniform wall-thickness; however, no distinct differences among the FLC based on the three instability criteria were observed.