Strain path′s influence on the elastic behaviour of the TRIP 700 steel

Abstract

a b s t r a c tThis paper deals with the analysis of the strain path 0 s influence on the elastic behaviour of TRIP 700 steel; it aims to validate the cyclic testing method to characterise inelastic behaviour of advanced high strength steels (AHSS). Different cyclic tests are done, where the strain path is changed from test to test. Large deformation strain gages are used to determine the inelastic behaviour of the specimens at macro-level. At a lower scale, stress measurements are carried out using the XRD technique during an in-situ tensile test: ferrite and austenite phases' stresses are measured before unloading and after loading again to study the strain path 0 s influence.By means of this work it is confirmed that the elastic strain path has no influence on the unloadingloading of this TRIP steel. These results prove that conventional loading-unloading cyclic testing is a valid methodology for a detailed characterisation of the elastic modulus and reliable numerical modelling of springback.

Elastic behaviour characterisation of TRIP 700 steel by means of loading–unloading tests

“…The influence of the pre-strain levels have been studied by the authors in a previous work (Mendiguren et al (2012)) concluding the invariability of the elastic behaviour of the material due to the elastic unloading-loading cycles. Therefore, as the elastic behaviour of the material is not affected by the number of experimental cycles or their pre-strain, non-equispaced pre-strain levels ε ps have been selected in this work as shown in Table 3.…”

“…Through this new proposed strain measurement method, some conclusions drown in previous works have been validated, while different data have been obtained on others. The characterization tests have been carried out by means of conventional tensile test and loading-unloading cycles (Mendiguren et al, 2012). The loading-unloading cyclic tests have been performed up to near 20%.…”

Characterisation and modelling of in-plane springback in a commercially pure titanium (CP-Ti)

“…2. Degradation in Young's modulus with progress of plastic deformation [1,[5][6][7][8][9][10][11][13][14][15][16][17][18][19]: as shown in Figure 8, the degradation in Young's modulus is significantly high which is orientation dependent. The measured degradations in Young's modulus were 20% for the samples at 90°to the RD at highest and 13% for those at 0°to the RD at lowest, and those of the samples at 45°to the RD were in between.…”

“…Earlier studies [1,7,8,10,11,[13][14][15][16][17] show a degradation in Young's modulus as a function of the level of plastic deformation for different alloys. This has usually been shown by comparing the initial elastic modulus, characterised using standard methods, at no plastic strain to those measured after various levels of plastic strain through interrupted tensile tests, consisting of a series of loading-unloading-loading steps on a same sample [5].…”

“…Different methodologies exist to study degradation in Young's modulus as a function of plastic deformation, such as interrupted uniaxial [1,7,8,[13][14][15]18] and biaxial loading-unloading-loading tensile tests [19,20], and pre-strained three-point bending tests [19,[21][22][23]. The former is the most reported method used for detailed characterisation of elastic modulus during plastic deformation [1,7,8,10,11,[13][14][15][16][17]. Despite the intensive application of interrupted tensile test technique, it has been argued that the pre-strained threepoint bending test provides measurement of degradation in elastic modulus during plastic deformation more accurately [19].…”