A Simplified Spot Weld Model for Finite Element Analysis

<div class="section abstract"><div class="htmlview paragraph">The serpentine belt's multi-scale problems in geometric size, which gives rise to a very large number of element and deeply low calculating efficiency, always bring obstacles when predicting the dynamic response of a serpentine belt driving system using three-dimensional finite element model (FEM). In this paper, a simplified finite element model is built which can accurately present the original serpentine belt's geometric characteristics such as cross-area and moment of inertia, as well as material characteristics such as stiffness and damping, etc. This simplified model is then used in a three-dimensional belt-drive model to simulate the dynamic characteristics of the belt-drive system. The results show that the tension fluctuation for the original serpentine belt and the simplified belt are in good agreement with each other which confirms that the simplified belt model can be used to predict the engine front end accessory drive system (EFEADS)'s dynamic characteristics. Furthermore, the simplified belt has greatly improved the calculating efficiency as it reduces element number and the minimum element size and can be modelled more easily compared with the serpentine belt, so the simplified model has a very important engineering significance especially when it is applied to the complicated EFEADS.</div></div>

<div class="htmlview paragraph">In early design phases vehicle safety testing has revealed the occurrence of both spot weld failure and sheet metal tearing that contributed to below specification performance. This would require redesign and additional testing to meet the specification. Because of cost and weight requirements in vehicle development, it is desirable to create efficient body designs for vehicle safety performance.</div> <div class="htmlview paragraph">To develop more efficient structures, it is useful to be able to predict both connection and material failure in a variety of loading conditions using finite element (FE) models. Two new FE methodologies were developed separately to aid in predicting these phenomena. Since it is a widely used explicit FE code, LS-DYNA<sup>™</sup> was chosen as the program with which to implement the new material and spot weld models. One methodology uses a force based failure criteria to model failure in, and next to, spot welds. A second methodology was developed to predict sheet material failure using the Forming Limit Diagram (FLD) for ferrous materials. These methodologies were confirmed separately using simple FE models and compared to actual test results.</div> <div class="htmlview paragraph">After each methodology was confirmed separately, the two new FE techniques were used in concert to predict automotive structural behavior with combined spot weld failure and sheet metal tearing present.</div>

Predicting the failure of spot welds remains one of the most important modeling challenges in automotive engineering. In essence, the structure surrounding a spot weld corresponds to a graded material with severe variations in the plasticity and fracture properties as a function of the distance to the center of the weld nugget. While it is common practice to identify hardness variations around a spot weld, a newly developed micro-tensile testing technique is used to characterize spatial variations in both strain hardening and fracture strains. Furthermore, a new experimental device is presented to subject spot welds to combined tension, shear and bending loads. Following a careful experimental characterization of resistance spot welds connecting two 1.5 mm thick DP600 sheets, a detailed finite element model is built which accounts for the identified property gradients. In addition, a simplified surrogate model for use in conjunction with coarse shell element meshes is also calibrated. Simulations are performed of all structural experiments to assess the range of validity of the detailed and simplified FE models. It is found that the detailed model captures the experimentally observed failure modes including changes in the location of fracture initiation as a function of the loading, while the simplified model is able to predict the spot weld strength with reasonable accuracy.

Beam-column joints play a critical role in the overall safety and load transfer mechanism of reinforced concrete frame structures, particularly under lateral and seismic loading conditions. Accurate assessment of joint behavior is essential for predicting structural performance and preventing progressive damage or collapse. Conventional experimental investigations provide reliable insights but are often limited by cost, time, and scalability constraints. In this context, simplified finite element modeling offers an efficient analytical alternative for evaluating joint response while retaining essential behavioral characteristics. This research presents an analytical investigation of beam-column joint behavior using a simplified finite element modeling approach aimed at balancing computational efficiency and predictive accuracy. The modeling framework incorporates key material nonlinearities, geometric compatibility, and boundary conditions relevant to typical reinforced concrete joints. Stress distribution, strain localization, stiffness degradation, and load-deformation response is examined under monotonic loading scenarios. The analytical results are compared with established theoretical expectations and trends reported in previous experimental and numerical studies to validate the modeling strategy. The findings indicate that simplified finite element models can effectively capture critical joint behaviors such as shear stress concentration, cracking initiation zones, and progressive stiffness reduction without resorting to highly complex constitutive formulations. The research highlights the sensitivity of joint response to mesh discretization, material idealization, and joint geometry representation. By demonstrating the feasibility of simplified modeling techniques, this work contributes to the development of practical analytical tools suitable for preliminary design evaluation, parametric studies, and academic research. The outcomes support the hypothesis that simplified finite element models, when appropriately calibrated, can serve as reliable indicators of beam-column joint performance, thereby reducing dependence on resource-intensive experimental programs while enhancing understanding of joint mechanics in reinforced concrete frame systems.

<div class="htmlview paragraph">This paper summarizes the results of a recent study on a fatigue predictive technique for spot-welded automotive structures. The technique makes use of an equivalent stress intensity factor (K<sub>eq</sub>) as fatigue parameter for life predictions. A series of fatigue tests were conducted by using different types of fatigue specimens and weld arrangements. Using the raw test data collected, fatigue properties were processed in the form of ΔK<sub>eq</sub> versus fatigue life by a fracture mechanics based stress intensity factor technique. It is demonstrated that the fatigue properties are consistent among all the specimens tested and relatively geometry-independent. With the stress intensity factor based fatigue properties, the predictive technique was applied to more complex specimens with non-symmetric weld configurations and non-uniform loading conditions (resulting in mixed-mode loading on each weld). The results indicate good correlation between life predictions and test data. Finally, the results of a series of sensitivity studies are presented concerning the effects of various FE modeling details on the accuracy of the predictive technique.</div>

Experimental and numerical study of T-shaped irregularly concrete-filled steel tube columns under combined axial loads and moments

<div class="htmlview paragraph">During the last decades one of the main challenge in the automotive field has been weight reduction to satisfy the EU's demands concerning fuel consumption and environmental aspects. Consequently, various materials are being considered. Using different materials for different automotive parts requires advanced joining techniques. The present work deals with the most frequently used joining technique, namely resistance spot welding. Additionally, laser welding is being considered, since it is obvious that this technique is being used for more and more parts.</div> <div class="htmlview paragraph">Since the welds of the dissimilar joints have to fulfill demands concerning formability, corrosion resistance and fatigue, the overall goal of this investigation is to find the best welding or joining parameters to achieve optimal joint performance in terms of structural integrity and part requirement.</div> <div class="htmlview paragraph">The steel grades involved in creating dissimilar joints are two austenitic stainless steel grades (EN 1.4301 (304) and EN 1.4318 (301LN)) and three ferritic non-stainless grades (ZStE340, DP600 and St14) with various thicknesses. The corresponding laser and spot welding parameters, microstructures, hardness mappings and mechanical properties were recorded. In laser as well as in spot welding the weld or nugget became fully martensitic. Correspondingly, the hardness clearly increased. The influence of the welding speed for laser welding and the welding current and post welding heat treatment (PWHT) during spot welding was investigated.</div>

<div class="section abstract"><div class="htmlview paragraph">A vehicle’s structure has more than 4000 spot welds, which can be considered as one of the main design criteria that affects the general stiffness as well as the durability of an automobile. Considering the essential role of finite element-based simulations of the spot-welded structures on the design phases of vehicle development, accuracy of analyses can be considered as one of the main concerns to meet the design objectives. This study examines the sensitivity of solid element spot weld modeling technique to nugget diameter. Comparative stress and multi-axial low cycle fatigue analyses are conducted for the inspection of the effect of weld diameter on solid element spot weld simulations. Displacement contours as well as local stress profiles at the vicinity of the spot welds are examined to evaluate the effect of nugget diameter on general stiffness and safety. Multi-axial low cycle fatigue analyses are conducted for the specimens composed of U-profiles, and different thickness levels are simulated for a set of nugget diameters. Simulation results are compared with the low cycle fatigue tests’ life cycles to determine the accuracy of the solid element spot weld modeling methodology and its sensitivity to nugget diameter.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Adhesively bonded steel hat section components have been experimentally studied in the past as a potential alternative to traditional hat section components with spot-welded flanges. One of the concerns with such components has been their performance under axial impact loading as adhesive is far more brittle as compared to a spot weld. However, recent drop-weight impact tests have shown that the energy absorption capabilities of adhesively bonded steel hat sections are competitive with respect to geometrically similar spot-welded specimens. Although flange separation may take place in the case of a specimen employing a rubber toughened epoxy adhesive, the failure would have taken place post progressive buckling and absorption of impact energy. The better-than-expected performance of an adhesively bonded component subjected to axial impact load is likely due to the evenly spreading adhesive over the entire flange areas of the hat section as compared to discrete spot welds in a conventional component. In the current study, numerical prediction of the behaviors of axially impacted adhesively bonded double-hat section components has been carried out using explicit finite element modeling and analysis. The formed plates in a double-hat section member are represented with shell elements while the adhesive in between either of the twin flanges is modeled with solid elements. A systematic approach is followed according to which finite element modeling parameters, especially those related to constitutive modeling, are verified by predicting the behaviors of single lap shear and T-peel joints under tensile loading conditions. On obtaining satisfactory correlation for the coupon-level tests mentioned, the modeling procedure is extended to the axial impact simulation of double-hat section components in a drop-weight test set-up, and the capability of predicting load-displacement responses and key crash parameters such as peak load, mean load and energy absorbed is demonstrated.</div></div>

<div class="htmlview paragraph">Modeling of spot weld failure is critical in CAE analysis for vehicle crash. Force-based criterion for spot weld nugget interfacial failure is still the most familiar one and commonly used in CAE practice. However, in vehicle crash, spot weld failures often occur in the form of nugget pullout, in which the sheet metal around the nugget, rather than the nugget itself, fails and thus results in the pullout. Compared to the nugget interfacial failure, the pullout mode is more ductile and involves in the materials in and adjacent to the heat-affected-zone (HAZ) around the nugget. In this study, material failures in and adjacent to HAZ are directly modeled using strain-based failure criterion. The model consists of spot weld nugget, HAZ, and base metal (BM). The metal materials inside and outside of HAZ are treated as different materials, and the zones and subzones around the nugget may have different failure strain values. This modeling technique has been correlated with a group of test results found in the literature. The tests include two loading conditions: lap-shear and cross-tension. The tested material is high strength steel HSLA 350.</div>

<div class="htmlview paragraph">Torsional fatigue tests of: spot-welded box-section beams were conducted to explain fatigue fracture phenomena, and a technique to predict fatigue life of spot welds in beams was developed. When a torsional moment acts on box-section beams that are hat beams with their flanges spot-welded to form closed sections, shearing force is transmitted through the spot welds. Based on theoretical analysis of stress distribution in the vicinity of spot welds and using strain values measured on the outer surface of spot welds, fatigue life of beams was successfully predicted. A technique to predict fatigue life of beams was developed by computing the load acting on spot welds in a beam and using fatigue strength data of a single-point spot-welded joint of the same load coponent.</div>

<div class="section abstract"><div class="htmlview paragraph">The Automotive industry’s use of digital technology such as Computer Aided Engineering (CAE) to perform virtual validation has progressed to effectively replace a large percentage of physical validation. This is primarily due to the increased accuracy and cost/time efficiencies that virtual validation offers compared to conventional physical prototyping and testing. With product development (PD) cycles becoming more compressed, CAE has assumed a more significant role in early, advanced design and structural evaluation. One of the areas where CAE is widely employed is in development of the Instrument Panel (IP) commonly referred to as the dashboard. For the purposes of this study, the term IP represents the plastic/polymer structure only, and not the full IP sub-system. The IP sub-system includes the structural member, the Cross Car Beam (CCB) assembly and all the IP mounted modules.</div><div class="htmlview paragraph">The primary objective of this exercise is to guide upfront IP design using a simplified representation of the IP sub-system. The CCB assembly is represented as a parametric, simplified and scalable beam model. This simplified CCB model can then be used to simulate the IP sub-system as soon as the studio “class A” surface data is available in conjunction with assumptions for the masses of key IP mounted modules. The exercise is expected to yield a reliable process to guide the IP design, for structural stiffness objectives, at early stages of the PD cycle. To prove the effectiveness of this process, it is implemented on several IPs from different vehicle classes, and the global frequencies of the resulting simplified models are compared to the fully contented, traditionally built models.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Welding is the longest automotive manufacturing process in terms of time. Approximately 95% of an actual body structure joining is consisted by spot welds. In this specific joining process, the panels are joined one against the other, via pressure and an electric current released by the welding machine. Some case studies are demonstrating that, by using CAE optimization algorithm, it is possible to reduce significantly the amount of spot welds, without loss of function or performance. This paper demonstrates a case study with a reduction of approximately ∼ 14 % of spot-welds in a body region of a vehicle, using these tools.</div></div>

<div class="section abstract"><div class="htmlview paragraph">A state of the art proprietary method for aluminum-to-aluminum joining in the automotive industry is Resistance Spot Welding. However, with spot welding (1) structural performance of the joint may be degraded through heat-affected zones created by the high temperature thermal joining process, (2) achieving the double-sided access necessary for the spot welding electrodes may limit design flexibility, and (3) variability with welds leads to production inconsistencies. Self-piercing rivets have been used before; however they require different rivet/die combinations depending on the material being joined, which adds to process complexity. In recent years the introductions of screw products that combine the technologies of <i>friction drilling</i> and <i>thread forming</i> have entered the market. These types of screw products do not have these access limitations as through-part connections are formed by one-sided access using a thermo-mechanical flow screwdriving process with minimal heat. The friction drilling, thread forming process, hereto referred to as "FDS," is an automated continuous process that allows multi-material joining by utilizing a screw as both the tool and the fastener. The process uses the friction caused by the rotating screw to pierce and extrude the material. Threads are then created in this formed extrusion which allows the fastener to be screwdriven into the parts. A final torquing then securely clamps together the sheets of material. This study explores the quality design space as represented by resultant joint geometry as a function of the critical process parameters of fastener force and drilling speed. Feasible design space regions are explored to determine how process parameters affect joint geometry, and strength testing performed to validate the findings.</div></div>

In this paper, a simplified aircraft system model is developed correctly emulating the nonlinear dynamics of complex aircraft models under closed-loop control. The simplified model is based on Dubins models used in optimization algorithms for trajectory control of multiple Unmanned Aeriel Vehicles (UAVs). Algorithms optimizing area coverage for reconnaissance based on UAV capabilities, fuel remaining, and time constraints require simple aircraft models providing ecient solutions in near real-time. However, the simplified models should accurately predict UAV dynamics for proper prediction. For this study, a realistic UAV simulation is developed including nonlinear aerodynamics and kinematics. A UAV autonomous navigation algorithm for waypoint-to-waypoint navigation is derived and integrated in the complex UAV simulation. A simplified system model based Dubins model is developed closely matching the full nonlinear UAV simulation. A Rhumb-line navigation algorithm including a velocity-hold and altitude-hold control system is used for closed-loop control. A navigation system utilizing trajectory planning with Dubins curves is also developed. Both control laws are implemented in a simplified Dubins model and tuned to match the full nonlinear simulation under autonomous control including provisions for head and tail wind conditions. Computer simulations are performed demonstrating waypointto-waypoint navigation with desired final heading trajectories for both the full nonlinear UAV model and the simplified Dubins simulation. Simulation time history analysis is used to verify the accuracy of the simplified model compared to the full nonlinear simulation model.