Among different parts of a vehicle, the body is the main load-bearing component and as a result, its durability is critical. Fatigue analyses are typically divided into different categories, the ...quasi-static methods and the dynamic methods. The aim of this paper was to compare the inertia relief and modal dynamic approaches for their formulation, accuracy and computation time. The chosen case study is the fatigue life of the vehicle body. By utilizing multi-body dynamics model and driving the vehicle on different standardized roads and by different velocities, the force and moment time histories which act on the body were calculated and later used by the finite element model for the stress analysis. Then, by using the structural stress method, the fatigue life of the vehicle spot welds were calculated and the results were compared for both quasi-static and dynamic approaches. The findings reveal that the modal dynamic method is almost 37 times more time-consuming than the inertia relief approach, but if accuracy is desired, it can be up to 96% more accurate. Also as predicted, at low frequency loading (less than 10% of the first nonzero frequency of the structure), there is no difference between the results of both methods.
Aluminum alloys are widely spread in many industrial sectors due to their desirable characteristics as low density, good formability, high specific strength, and good resistance to corrosion. ...Autogenous laser welding is a technology that enables the use of these materials in the industrial process due to its high repeatability, reliability, and ease of automatization. In particular, in automotive applications, Al-alloys are welded in lap-joint configurations with more than 2 layers of material. The welding condition should be monitored in order to detect the complete penetration, hence guaranteeing the appropriate weld resistance. The use of non-invasive and coaxial monitoring solutions is highly desirable for the identification of weld defects during the process. This study investigates an autogenous laser welding process and monitoring in the double lap-joint configuration of sheets of AA 5754. First, the process parameters are investigated to identify the geometrical and mechanical characteristics of the resultant welding seams at different process conditions. The employed high-brilliance 3 kW fiber laser provided the possibility of reading the back-reflected light signal from an internal photodiode. The capability of this signal to be used as a non-invasive, coaxial, and remote monitoring system in order to predict the process outcome was tested. In the experiments the back-reflected light intensity could be correlated to the weld seam width at the second interface, as well as the strength of the joint to shear. Finally, the monitoring signal behavior was demonstrated under simulated weld defect conditions. The results show that weld anomalies such as lack of penetration, misalignment, and gap formation can be sensed through the monitoring approach.
Owing to the expensive and time-consuming nature of durability experiments, finite element based durability analysis is quite prevalent in the automotive industry. Numerical fatigue life analyses are ...typically divided into two different categories, the quasi-static methods which are faster and the dynamic methods which are more accurate. The aim of this paper is to compare the inertia relief and modal dynamic approaches in terms of formulation, accuracy and computation time. The chosen case study is the fatigue life of the vehicle body which is considered the main load-bearing component in a vehicle. By utilizing multi-body dynamics model and driving the vehicle on different standardized roads and by different velocities, the loadings, which act on the body are calculated and later used for the stress analysis. Then, by using the structural stress method, the fatigue life of the vehicle spot welds is calculated and the results are compared for both approaches. The findings reveal that the modal dynamic method is almost 37 times more time-consuming than the inertia relief approach, but if accuracy is desired, it can be up to 96% more accurate. Also as predicted, at low frequency loading, there is no major difference between the results of both methods.
Vehicle lightweighting strategies must deliver sustainable returns to customers and society. This work evaluates the sustainable return on investment (SROI) of lightweighted advanced high strength ...steel (AHSS) and carbon fiber reinforced polymer (CFRP)-intensive multimaterial bodies in white (BIWs) for automobiles. The SROI depends on the lightweighted BIW’s manufacturing cost and the difference in sustainable cost between a baseline (mild steel) BIW and the lightweighted alternative. The sustainable cost is the sum of the customer’s lifetime fuel (or electricity) costs and the costs of environmental externalities. A cradle-to-grave life cycle assessment (LCA) was conducted to quantify the environmental impacts of CFRP and AHSS BIWs in gasoline-fueled cars, bioethanol (E85)-fueled cars, and battery electric vehicles (BEVs) driven for a lifetime distance of 200 000 km. For cars fueled with gasoline- or corn-based bioethanol, the CFRP BIW yielded the lowest SROI; the AHSS BIW performed best for BEVs and cars fueled with wood bioethanol. However, the commercial availability of recycled carbon fiber should increase the SROI of the CFRP BIW in the future. Additionally, the SROI of CFRP BIWs is maximized when carbon fiber production is done using energy from a low carbon-intensity electric grid or decentralized sources such as waste-to-energy incineration plants.
The present study investigates the evolution of the residual stresses in TWIP steels induced by manufacturing chain for the production of automotive body-in-white. Two different manufacturing routes ...were considered. The first route encompassed a plastic deformation prior to the welding stage, whereas the second involved the spot welding followed by a baking treatment. A convergent approach was adopted to isolate the effects of the first and final manufacturing steps. The findings showed that the plastic deformation prior to the welding stage is not annihilated by the welding thermomechanical cycle. Abrupt hardness gradients along small material fractions are observed. The residual stresses state changes, although its profile is still defined by the welding stage. The post-weld bake treatment showed to promote slight residual stresses relaxation, but it is not effective in inducing the same post-weld residual stresses state for different RSW parameters set.
The body-in-white simulation model of a certain commercial vehicle was established to make a numerical analysis of the vehicle body static stiffness in this research. Meanwhile, the effectiveness of ...the simulation model was verified using the physical test of body-in-white static stiffness. Research results showed that the error of body-in-white static stiffness test and simulation analysis was within the range of ±10 %, which could reduce the test cost and guarantee the test precision. The research findings do provide a better application value and references for vehicle engineering developers.
This article presents a hybrid method combining a modified non-dominated sorting genetic algorithm (MNSGA-II) with grey relational analysis (GRA) to improve the static-dynamic performance of a ...body-in-white (BIW). First, an implicit parametric model of the BIW was built using SFE-CONCEPT software, and then the validity of the implicit parametric model was verified by physical testing. Eight shape design variables were defined for BIW beam structures based on the implicit parametric technology. Subsequently, MNSGA-II was used to determine the optimal combination of the design parameters that can improve the bending stiffness, torsion stiffness and low-order natural frequencies of the BIW without considerable increase in the mass. A set of non-dominated solutions was then obtained in the multi-objective optimization design. Finally, the grey entropy theory and GRA were applied to rank all non-dominated solutions from best to worst to determine the best trade-off solution. The comparison between the GRA and the technique for order of preference by similarity to ideal solution (TOPSIS) illustrated the reliability and rationality of GRA. Moreover, the effectiveness of the hybrid method was verified by the optimal results such that the bending stiffness, torsion stiffness, first order bending and first order torsion natural frequency were improved by 5.46%, 9.30%, 7.32% and 5.73%, respectively, with the mass of the BIW increasing by 1.30%.
In order to improve the lightweight level, crash safety performance and optimization design efficiency of body-in-white (BIW), this article proposes a lightweight multi-objective optimization design ...method for mixed-material body. The implicit parametric model of the BIW is created by using SFE-CONCEPT software, and the validity and correctness of the model are verified by tests. Material, shape and dimension parameters are introduced as design variables for design of experiments (DOEs), and 26 important design variables are screened out by combining contribution analysis with nonlinear main effects analysis. The approximate model method is used to fit the Kriging surrogate model and the RBF surrogate model, and it is found that the RBF surrogate model can better reflect the relationship between nonlinear crash performance and optimization variables. A hybrid method combined entropy weighted grey relational analysis (EGRA) with modified non-dominated sorting genetic algorithm (MNSGA-II) is proposed to carry out the lightweight multi-objective optimization of BIW in front crash and side impact, which improves the population diversity of multi-objective optimization problems and quantifies the comprehensive performance of each scheme. Comparing and analyzing the optimization platform recommending scheme, the technique for order preference by similarity to an ideal solution (TOPSIS) method preferring scheme and the EGRA method optimum scheme, it is found that EGRA method can obtain the optimal compromise scheme, and the performance improvement of the BIW are more obvious and the improvement rates are also more balanced. The results verify the feasibility of the ranking method, avoid the blindness of optimal solution selection, and establish an objective evaluation method of multi-objective optimization results. The optimization results show that the improvement rates of the BIW lightweight coefficient, the average value of the maximum acceleration of the B-pillars on both sides during the front crash, and the maximum intrusion displacement of the B-pillar chest during the side impact have reached 11.5%, 6.5%, and 6.8%, respectively. Other performance response improvement rates are also above 3.3%, the lightweight and crash safety performance are significantly improved.
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