Study On Failure Criterion Of Aluminum Alloy For Manufacturing Process

In the global competitive environment, the performance indicators of complexproducts are continuously upgrading, which brings new challenges in meeting theever-increasing manufacturing requirements. For example, some auto body productsneed to reach a dimensional accuracy of±0.5mm, while that of large-scale thin-walledaircraft components reach up to±0.125mm. Computer simulation technology providesfast, efficient and reliable results for advance evaluation of the manufacturing quality.With the increasing complexity of products and production environment,manufacturers increasingly rely on simulation to evaluate and refine the design.Failure of material is a common phenomenon in the manufacturing processes. Itis crucial to establish a failure criterion in the simulation to identify any possibleinstability or fracture failure before conducting costly tryout experiments. Developingreasonable and practical failure test and prediction methods has always been achallenging task for the scientific and engineering community.In this study, the warm forming and the cutting process were selected as thebackground for modeling material failure criterion. Based on the comparison andevaluation of the corresponding research, the fundamental theory for modelingmaterial failure criterion was studied. An approach for predicting the forming limit inwarm forming of aluminum alloy sheet was proposed and applied in the simulation.Besides, the failure criteria under cutting conditions was developed and applied in thecutting simulation of aviation aluminum alloy. The following three aspects of effortswere made:(1) Study on the fundamental theory for modeling material failure criteria fortypical manufacturing processAn extensive review of previous theoretical and experimental work on materialfailure criteria modeling was provided. A number of novel flow stress and multi-axialyield behavior tests and modeling methods were introduced. Several modelingapproaches pertaining to theoretical analyses of necking failure were outlined and a comparative study of the above FLD theoretical models and the experimentalvalidation were carried out. Some findings were highlighted and further discussed.(2) Study on the temperature and strain rate dependent forming limit predictionmethod in warm forming of aluminum alloy sheetThe temperature and strain rate have a significant effect on the formability ofaluminum alloy sheet in warm forming process. The extended Backofen constitutiveequation was developed, in which the material parameters were fitted as a function oftemperature and strain rate. Based on M-K theory, the forming limit of5083Al-Mgalloy sheet at elevated temperatures was calculated by using Logan-Hosford yieldfunction. Good correlation between the calculation result and the experimental datawas indicated, which verified the accuracy of the theoretical approach at differentstrain rates and temperatures. The calculated forming limit was then applied in thewarm forming simulation as the failure criterion. The prediction was compared withthe experimental data to show the accuracy and validity of the theoretical approach.(3) Study on the material failure behavior and failure criterion in cutting ofaviation aluminum alloyMaterial failure behavior and the typical stress state in cutting conditions wereinvestigated based on the orthogonal cutting test of AA7075-T651aluminum alloy.The failure criterion formula was then derived analytically based on the theoreticalanalysis of the compression-torsion loading of thin-walled cylinder. In order tosimulate the failure behavior of AA7075-T651under the typical stress state in cuttingconditions, an inner high-pressure piercing fracture test was developed. Theparameters of the developed failure criterion were calibrated through a comparison ofthe simulation predictions and experimental results. The developed failure criterionwas then applied in the cutting simulation of AA7075-T651. Comparison of thesimulation predicted and experimentally acquired chip formation, cutting force andcutting temperature results was demonstrated to show good agreement.