Large Deformation Behaviors Of Aluminium Alloy Welded Joints And The Basic Components For Automobile

As a result of the need for the modern automotive design to address energy savings and environmental issues,the aluminium space-frame has been used more and more widely.To assess the crashworthiness of the space-frame,designers have to think about the cost and complexity of research,it's impossible to do too much crashing tests.Therefore,FEM simulation takes the main part during design process.Quite a lot of work has been done by means of explicit FEM code in automobile industry.But some times the simulation did not make a good agreement with the experiments.This problem was raised not because of software precision,but the incomplete models for materials and welded joints.The main problems are as following:1)By now,the current material models and parameters for simulation of large compacted deformation are still not satisfied for material damage and failure characterization under different stress state,high strain rate loading and with anisotropy considered.2)The welded joint is still pivotal connecter for ASF.But the mechanism of distortion and failure are not understood very well.It's hard to handle mechanical properties for inhomogeneous welded joint.There are no accurate material characterization and models to use;therefore the poor joint model causes poor simulation results.3)For the crashworthiness of car body,the FE models for welded joints are still limited. Especially for some arc welded joints,little work has been done in numerical modeling, except for the spot welded joint and glued joint.Developing of simplified joint model are some gaps in crashworthiness simulation of car body.Research was carried out around those issues above.First of all,laser welding,TIG welding and Stir friction welding were performed for the aluminium alloy 5052H34 and 6063T5.Three typical welded joints were made.The microstructure and mechanical properties were tested to identify joint specific inhomogeneous features.The second part of this paper discussed the material characterization for the base material aluminium alloy 5052H34.Static and dynamic uniaxial tension test,notch tension test as well as double notch tension test were carried out combined with SEM microstructure observation, and numerical simulation to analysis the material deformation,damage and failure behavior with anisotropy,different stress state,strain rate,and temperature as well.On the basis of achieved results,a constitutive relation considering dynamic soften and work harden effect was obtained.Two damage models Gurson and Johnson cook were used to describe the damage and failure behavior,which fitted well with FEM analysis.The third part mainly studied the inhomogeneous deformation of welded joints.Material characterization was made for different parts of joint.The welded joint was divided into 10 micro zones.For each zone,the specific following curve was identified by means of the Small Punch Test(SPT)combined with an inverse finite element(FE)arithmetic.After that,the inhomogeneous deformation evaluation of joint was analysis by meshing the sample and taking video record.Test data was compared with numerical results.The forth part mainly discussed numerical modeling for welded joint.The material characterization and material modeling were based on the SPT test.The geometrical models of welded joints were copied from the real size of structure or samples.Combincd the geometrical part and material model together,an accurate finite element model were established.A function of welded joint equivalent width expressed by the strength mismatch coefficient,geometrical parameters was obtained on the basis of inhomogeneous deformation mechanism.At the end of this section,a simplified model for welded joint was presented, which can be embedded in the FE model of car body in the next step.The fifth part made analysis of the crashworthiness of basic components with welding or without welding.The influence of structure size,loading condition,and local mechanical behavior on the deformation and failure of whole component was studied.Some advices were supplied for structure optimizing.At the same time,validation was made for the numerical model of welded joint established in previous part.The results showed that the welded joint numerical model was credible.The sixth part indicated how to carry out a crash simulation with embedded simplified welded joint model on the paralleling computing platform.The dynamic response of ASF and action among internal parts components under dynamic loading were analyzed with example of car compacting to rigid post.Some hidden troubles for car body safety design were point out and analyzed as well.