Research On Simple Shear Experiment Of Laser Tailor Welded Blanks Based On DIC

With the development of automotive lightweight technology and cost control requirements of car manufacturers, laser welding technology has been widely used in vehicle manufacturing. Traditional research on formability of laser tailor welded blanks focus on several universal tests whose lim itation is obvious that is they can not acquire the deformation under simple shear condition and the relationship between stress and strain in large strain range. T his paper focuses on the mechanical properties of laser tailor welded blanks under the load of which simple shear is dominant.(1) Laser tailor welded blanks of same base metal and same thickness were prepared. A fixture was designed which was used in the simple shear test and cyclic shear test. Black lines were drawn on the surface of blanks before the tests. Videos of the gauge area were recorded so that the strain could be calculated.(2) One method to calculate strain based on DIC(Digital image correlation) technique was proposed. Median filter and close operation was chosen as image preprocessing and morphology operation. Thinning of the black lines on the surface is the key point of acquiring the strain. A s traditional thinning method could not exclude longitudinal distractions, a new thinning method was proposed which could eliminate the longitudinal distractions and retain the black lines effectively. Through integrating the above methods, a complete set of arithmetic was written in MATLAB, by which the strain could be measured accurately.(3) Simple shear test and cyclic shear test were carried out and the stress-strain curve under different load path was acquired. It is found that the ability to resist deformation of DP390 laser tailor welded blanks is weaker than the original material in elastic stage but stronger in plastic stage. Rounding of the reverse flow curve and reducing of the yielding strength under reve rse loading were found and discussed. Strain hardening characteristics was calculated in different tests. It is found that the strain hardening characteristics of laser tailor welded blanks in cyclic shear test increases as the growth of the number of cycl es. Laser tailor welded blanks is more and more close to the ideal elastic body in cyclic shear test.