Design Of Automotive Structures Research Articles

Crash Box Impact Energy Absorption

Abstract: Crashworthiness parameters like internal energy absorption and crush force efficiency are the key constants in evaluating the component crashworthiness and its safety in the design of automotive structures for crashworthiness, there is an immense requirement for null strain sub modules that provide a rigid room of survival area for the occupants and deformable sub modules. Which can dematerialize the kinetic energy effectively? The front crash box of an automotive car is one of the most important deformable components which dissipate kinetic energy while frontal crash, which is the most persistent crash situation, affects the entire automotive structural behavior. In this research, quasi-static axial loading response and crashworthiness characteristics of empty hollow tube have been investigated through experimental and numerical simulations. The axial quasi-static loading was executed at a feed rate to evaluate the crashworthiness constants of each sample against quasi-static loading. The supremacy of feed rate empty hallow structures were pursued. The numerical simulation of quasi-static test was performed in accordance with explicit finite element algorithm of LS-DYNA in order to investigate and justify the crashworthiness of each variety of specimens with experimental results.

Investigation into the Effect of Interlock Volume on SPR Strength

During the design of automotive structures assembled using Self-Piercing Rivets (SPRs), a rivet and die combination is selected for each joint stack. To conduct extensive physical tensile testing on every joint combination to determine the range of strength achieved by each rivet-die combination, a great deal of lab technician time and substrate material are required. It is much simpler and less material-consuming to select the rivet and die solution by examining the cross sections of joints. However, the current methods of measuring cross sections by measuring the amount of mechanical interlock in a linear X-Y direction, achieved with the flared rivet tail, do not give an accurate prediction of joint strength, because they do not measure the full amount of material that must be defeated to pull the rivet tail out of the bottom sheet. The X-Y linear interlock measurement approach also makes it difficult to rapidly rank joint solutions, as it creates two values for each cross section rather than a single value. This study investigates an innovative new measurement method developed by the authors called Volumelock. The approach measures the volume of material that must be defeated to pull out the rivet. Creating a single measurement value for each rivet-die combination makes it much easier to compare different rivet and die solutions; to identify solutions that work well across a number of different stacks; to aid the grouping of stacks on one setter for low-volume line; and to select the strongest solutions for a high-volume line where only one or two different stacks are made by each setter. The joint stack results in this paper indicate that there is a good predictive relationship between the new Volumelock method and peel strength, measured by physical cross-tension testing. In this study, the Volumelock approach predicted the peel strength within a 5% error margin.

A size optimization procedure for irregularly spaced spot weld design of automotive structures

Spot weld layout design for body structures is of practical significance to both manufacturing cost control and performance improvement in the automotive industry. In this work, by using a typical thin-walled double-hat section beam as a proxy, a parametric study was first carried out to reveal the effects of spot weld layout design on the structural performances under both static and impact loading conditions. To overcome the limitation of traditional uniformly spaced spot weld configuration, an innovative size optimization based procedure was proposed for the spot weld layout design of automotive structures with irregular spacings. In this procedure, sampling points that satisfy both equality and inequality constraints are obtained by introducing the mixture design of experiment method. The leave-one-out cross validation strategy is used to bring the training samples into full play in building surrogate models for structural analyses with high accuracy. Moreover, the NSGA-II is incorporated to search the Pareto front of the multiobjective optimization problem. Application of the proposed procedure on the thin-walled double-hat beam resulted in 33.3% spot welds reduction from the uniformly spaced baseline design, without weakening the structural static and NVH performances by more than 3%. The reliability and effectiveness of the proposed procedure is thus proved.

Bending collapse of dual rectangle thin-walled tubes for conceptual design

In engineering, the bending deformations of thin-walled tubes mostly are under three-point loading. However, for the dual rectangle thin-walled tube (DRTWT), the theoretical prediction of the three-point bending collapse is still an unsolved problem. In this paper, the three-point bending collapse of the DRTWT is innovatively investigated using theoretical prediction and experimental verification. The global energy equilibrium theory is applied to derive the bending characteristic of the DRTWT. It is assumed that all the bending energy is absorbed and distributed along the hinge lines and in the toroidal surfaces during the bending collapse. The analytical results show good agreement with the experimental results. Finally, a simplified bumper structure of automobile is created by using beam elements and spring elements with the derived bending characteristics, which can effectively replace the detailed finite element model (FEM) to accelerate the crashworthiness design of automotive structure at the conceptual design stage.

An adaptive multi-step varying-domain topology optimization method for spot weld design of automotive structures

Spot welds are widely used to join metal stamping parts in the automotive industry. The number and layout of spot welds have direct impacts on both the mechanical performances of the vehicle and the manufacturing cost. The traditional methods including the 0–1 programming method, the size optimization method, the direct optimization method, and the single-step topology optimization (SSTO) method all have major drawbacks and are not suitable or efficient for spot weld layout design of an automotive structure. In this work, we propose a new method called multi-step varying-domain topology optimization (MVTO) method for spot weld design of automotive structures to balance structural performance and manufacturing cost. Based on a multi-step topology optimization framework with adaptive and varying design domains, the MVTO method can find a better layout design of the spot welds in a more efficient way compared to the existing methods. Limited engineering experiences are required and adverse human factors are eliminated in the spot weld design process with MVTO. To assist the application of MVTO method and to realize design automation, a new modeling approach is also developed to connect the continuous connection elements (CCEs) of the spot welds to the shell elements of the welded structure. Two case studies involving a simple single-hat beam and an automotive B-pillar show that the proposed MVTO method is reliable and effective for spot weld design of automotive structures. It has also been demonstrated that the MVTO method is superior to the direct optimization method and the SSTO method in terms of spot weld number reduction and welded structure performances, thus has a great potential for spot weld design of complicated automotive structures.

Simplified crashworthiness method of automotive frame for conceptual design

The crashworthiness design of automotive structure is crucial to ensure the safety of passengers. Lumped parameter models, multi-body models, plastic frame models and detailed shell element models were all introduced to simulate the collision process of automotive structure. However, plastic frame models were only confined to use box beams. Therefore, this paper presents a comprehensive crashworthiness design of plastic frame model, which can innovatively create complex thin-walled beams with arbitrary cross-sectional shapes, such as open, single-cell, double-cell, three-cell and four-cell sections. Numerical example verified that the proposed model can effectively replace detailed shell element model to accelerate the crashworthiness analysis of automotive structure, especially for the conceptual design.

Lightweight Body-In-White Design Driven by Optimization Technology

Structural optimization technologies are increasingly applied to lightweight automotive structural design. In a body-in-white (BIW) development project, optimization technologies are applied in three steps that are seamlessly integrated into engineering practice. By following a design-driven approach, an innovative design that was 50.65 kg lighter than the base design was achieved. First, topology optimization was used to investigate the optimal material distribution in a given design space, and helped in extracting the main load path, while considering crashworthiness, NVH, and static stiffness performance requirements. In the second step, the effective design of a beam cross-section and feasible joints was carried out based on optimization technology and expert knowledge. In this step, the deep involvement of manufacturing process experts on stamping and joint connection feasibility analysis increased the chance of success remarkably. The sensitivity analysis, topography optimization, and gauge optimization of the created draft 3D BIW frame comprised the last step before finalizing the initial design. The new design was validated by full load case simulations, including full vehicle crashworthiness analysis, mode frequency, and body mount point dynamic stiffness analysis, and BIW stiffness and component attachment stiffness analysis. The validation results indicate that the new BIW design achieves the performance goal, while being 13.3% lighter than the base design.

Multidisciplinary design optimisation methods for automotive structures

Multidisciplinary design optimisation (MDO) can be used as an effective tool to improve the design of automotive structures. Large-scale MDO problems typically involve several groups who must work ...

An experimental and numerical scrutiny of crashworthiness variables for square column with V-notch and groove initiators under quasi-static loading

AbstractCrashworthiness parameters like internal energy absorption and crush force efficiency are the key constants in evaluating the component crashworthiness and its safety. In the design of automotive structures for crashworthiness, there is an immense requirement for null strain submodules that provide a rigid room of survival area for the occupants and deformable submodules which can dematerialize the kinetic energy effectively. The front crash box of an automotive car is one of the most important deformable components which dissipate kinetic energy while frontal crash, which is the most persistent crash situation affects the entire automotive structural behavior. In this research, quasi-static axial loading response and crashworthiness characteristics of empty hollow tube, empty hollow tube with V-notch and empty hollow tube with horizontal groove have been investigated through experimental and numerical simulations. The axial quasi-static loading was executed at a couple of feed rates to evaluate t...

Ultrasonic spot welded 6111-T4 aluminum alloy to galvanized high-strength low-alloy steel: Microstructure and mechanical properties

Multi-material design of automotive structures for lightweighting solutions inevitably involves dissimilar joining of lightweight aluminum alloys with steels. Solid-state ultrasonic spot welding (USW) has recently received significant attention due to its high energy efficiency in comparison with conventional fusion welding techniques. In this study USW technique was used to join Al alloy 6111-T4 to galvanized high-strength low-alloy (HSLA) steel at different welding energy levels. During USW rapid interdiffusion of Zn and Al resulted in the formation of Al-Zn eutectoid/eutectic interface layer due to fast temperature rise and high strain rate. Part of this diffusion layer was squeezed out around the nugget edge in higher welding energy conditions, creating an additional brazing effect. The tensile lap shear load increased with increasing welding energy, reached a peak value, then decreased with a further increase in energy. Two major types of failure mode, namely interfacial failure and transverse-through-thickness (TTT) failure, were observed during tensile lap shear tests. The samples welded at 2000J exhibited a longer fatigue life than those welded at a welding energy of 1000J. During fatigue interfacial failure occurred at higher cyclic load levels, while TTT failure happened at lower cyclic load levels.

An evaluation of simple techniques to model the variation in strain hardening behavior of steel

It is important to consider variations in material parameters in the design of automotive structures in order to obtain a robust and reliable design. However, expensive tests are required to gain complete knowledge of the material behavior and its associated variation. Consequently, due to time and cost constraints, simplified material scatter modeling techniques based on scatter data of typical material properties provided by the material suppliers are used at early design stages in simulation-based robustness studies. The aim of this paper is to study the accuracy of the simplified scatter modeling methods in representing the real material variation. The simplified scatter modeling methods are evaluated by comparing the material scatter obtained by them to the scatter obtained by complete tensile tests, which are obtained after detailed time-consuming experimental investigations. Furthermore, an accuracy assessment is carried out based on selected responses from an axially-crushed, square tube made from DP600 steel.

Energy absorption of aluminum alloy thin-walled tubes under axial impact

Aluminum alloys are important technological materials for achieving the lightweight design of automotive structures. Many works have reported on the deformation and energy absorption of thin-walled tubes. Multicorner tubes with extra concave corners in the cross section were presented in this study to improve the energy absorption efficiency of aluminum alloy thin-walled tubes. The axial crushing of square and multicorner thin-walled tubes was simulated with the same cross-sectional perimeter. The method of folding element was applied to predict the crushing behavior of the thin-walled tubes under axial impact. The corners on the cross section were discussed to determine their effect on the energy absorption performance of thin-walled tubes. Results showed that the increasing performance of energy absorption of aluminum alloy thin-walled tubes was caused by the increasing number of corners on the cross section of multicorner tubes. Both the number and size of corners had an important effect on the crushing force efficiency of multicorner tubes. The maximum crushing force efficiency of multicorner tubes was 11.6% higher than that of square tubes with the same material consumption of thin-walled tubes. The multicorner tubes with 12 corners showed better energy absorption performance than the tubes with more than 12 corners; this high number of corners could lead to the small size of corners or unstable deformations. The high energy absorption performance of multicorner tubes prefers increasing the corner number and corner size of adjacent sides at the same time.

Multi-cornered thin-walled sheet metal members for enhanced crashworthiness and occupant protection

Crash energy management in frontal crumple zone of the automotive body is one of the key elements for the design of automotive structure. Improving energy absorption characteristics reduces the magnitude of forces transferred to the occupant compartments. Here, a new strategy has been proposed to improve energy absorption efficiency of thin-walled columns by introducing extra stable corners in the cross-section. Several profiles of multi-corner thin-walled columns obtained through this strategy were presented and their crashworthiness capacities under axial crush loading were investigated analytically, experimentally, and numerically. First, explicit formulations for predicting the mean crushing force of multi-corner thin-walled columns were derived using the theory of super folding element (SFE). Predicted results of these formulations showed a good agreement with the results of quasi-static experiments and CAE simulations, which were performed by explicit non-linear finite element code through LS-DYNA. Based on this agreement, other significant crashworthiness assessment parameters were then investigated experimentally and numerically. Newly introduced 12-edge section with high energy absorption capacity was developed and its dominance was established through the responses in quasi-static experiments and CAE simulations. Finally, the foundational dominance of the 12-edge section was extended to the dynamic environment through a full vehicle crash test simulation to evaluate overall reduction in crashworthiness parameters which reflected occupant safety. Interestingly, in the case of using 12-edge section as crush absorbers, specific energy absorption (SEA), dash intrusion and maximum occupant’s chest deceleration showed significant improvement, compared to the baseline design which used a rectangular section.

Compression-after-impact (CAI) performance of epoxycarbon fibre-reinforced nanocomposites using nanosilica and rubber particle enhancement

One of the problems in the design of automotive structures and body parts made by fibre reinforced composites is that these materials are susceptible to a small energy impact caused by for instance, accidental tool drop during maintenance or stone strike while in operation. This often lead to a barely visible impact damage which causes reduction in compressive strength of the composite part. To increase the impact tolerance of the composites, toughening agents like silica nanoparticles and rubber particles can be utilized to toughen the resin. To understand the effect of the particles enhancement, the impact tolerance was evaluated utilizing Compression After Impact (CAI) test after the impact induced by gas- gun impacting equipment. The results from CAI test after 20 J impact (high energy stone strike) shows about 30% improvement in residual compressive strength for the nanosilica enhanced composite compared to unmodified CFRP. Also C-scan results after 7 J impact shows about 50% smaller delamination area for the nano-enhanced composite.

Modeling and characterization of spot weld material configurations for crash analysis

To achieve an effective design of automotive structures, a material's mechanical properties are crucial, especially in welded structures that are susceptible to impact loading, such as in vehicle collisions. The primary objective of this research is to characterize resistance spot welding (RSW) for steel material and to develop an equivalent simplified weld model using material characterization. A secondary objective is to investigate friction stir spot welding (FSSW) for a material flow study using a smooth particle hydrodynamics (SPH) formulation and to compare it with RSW. During the initial phase of this study, friction stir welding (FSW) is investigated for temperature evolution, plastic strain, and material flow using finite element (FE) simulations, which are carried out using an elasto-plastic model. A heat source FSW model is developed to predict the thermal effect. FSSW results are compared with the results from RSW, reaching the conclusion that RSW is still a better method for the automotive industry. The necessary conditions for all RSW modeling are virtual test data that exist for spot-welded specimens. After developing a simplified weld model, the parameters gained from the sample specimen are transferred to the simulation of components tests. Components of a test especially designed for the connection failure illustrate that neglecting a spot-weld failure leads to altered energy absorption. Vehicle-level test also considered in this evaluation. Finally, to address the overdesigning issue, an optimization procedure is carried out using the I-sight software design methodology for vehicle mass reduction. Thus, a suitable modeling approach is investigated numerically for mapping the spot weld in a crash simulation. Further development of the analytical methods and user-defined material would be extremely beneficial; however, the proof of concept successfully developed in this dissertation satisfies its objective.

Shape and sizing optimisation of automotive structures with deterministic and probabilistic design constraints

This paper presents the results of a study on the combined shape and sizing optimisation of automotive structures while examining the effects of different design constraints and associated uncertainties on reliability and efficiency of the optimum designs. Nonlinear transient dynamic finite element analysis is used for full- and offset-frontal crash simulations of a full vehicle model. Surrogate models are developed for the intrusion distance and peak acceleration responses at different vehicle locations based on the material and geometric characteristics of the rail component. The obtained solutions provide insight on the effect of uncertainties in optimum design of automotive structures.

Creep behavior of a continuous strand, swirl mat reinforced polymeric composite in simulated automotive environments for durability investigation: Part I: experimental development and creep-rupture

Experimental methods were developed to simulate automotive environments and investigate the creep-rupture behavior of an isocyanurate base polyurethane matrix with a continuous strand, swirl mat E-glass reinforcement. The material under stress was exposed to various simulated automobile service conditions to test its creep-rupture properties. Results showed that environment had substantial effects on its creep strength durability. The resulting data were analyzed for deriving experimental based equations. Proposed guidelines and stress reduction factors were developed for automotive structural design applications.

Creep behavior of a continuous strand, swirl mat reinforced polymeric composite in simulated automotive environments for durability investigation: Part II: Creep-deformation and model development

Creep deformation behavior of an isocyanurate base polyurethane matrix with a continuous strand, swirl mat E-glass reinforcement was investigated for dimensional stability in automotive structural applications. Experimental data were generated in various simulated automotive service environments and analyzed to develop engineering models. Test results showed that environment had substantial effects on the creep deformation properties. Creep deformation design guide lines with respect to temperature, stress level and time have been proposed, environmental reduction factors for creep deformation suggested for automotive structural design applications.

Development of simplified models for design and optimization of automotive structures for crashworthiness

Simplified models can be useful for up-front design of automotive structures for passenger safety during crash. Formulations based on the system identification approach are presented for development of simplified models for simulation and design for automotive crash environment. Numerical crash data available from experiments or simulations are used in the development of such models. Parametric as well as nonparametric formulations of the problem are investigated. Standard nonlinear programming optimality conditions and methods are used to solve the resulting nonlinear identification problem. Simple numerical examples are solved to illustrate the proposed formulations and methodologies. As a practical example, the front horn of an automotive structure is replaced by a single degree of freedom system (SDOF). Two basis functions that identify the given target data are studied: Hat functions (piecewise linear) and Chebyshev polynomials. Effects of the number of design variables on the final solution to the problem are investigated. In addition, using the identified SDOF model, redesign of the front horn to improve its performance is discussed.