Issue 49

Y. Saadallah et alii, Frattura ed Integrità Strutturale, 49 (2019) 666-675; DOI: 10.3221/IGF-ESIS.49.60 669     n e ve e vp ve e H                    (6) replacing the elastic strain, the viscoelastic strain and its velocity by their formulas, and considering that the rate of elastic strain is zero, we obtain: 1 exp exp n e vp ve ve ve Kt Kt H K E                                                                  (7) Since the above equation is non-linear, numerical methods must be used for its resolution. Several methods are used to solve this kind of problem. Here is favored the bisection method [32]. The implementation is done under Matlab. M ATERIAL AND EXPERIMENTATION Material of study he material under study is a polyamide 6. It is a technical thermoplastic named TECAMID 6 sold in sheets 7 mm thick. The conditions under which the tests are carried out are summarized in a temperature of 300 K and a humidity of 20%. The specimen’s geometry was established according to ASTM D638. They were cut by CNC milling. Testing machine The test machine is a INSTRON 5969 with a capacity of 50 KN. It is equipped with a contactless video extensometer. This one allows to correct some problems like those related to the sliding of the edges of knife and the inertia of moving parts. The data is processed using the Bleuhill 3 control and acquisition system. perimental results Tensile tests at different constant strain rates are conducted. The strain rates correspond to the speeds of the crosshead movement. They are of the order of (0.0000646, 0.000625, 0.00612, 0.0556) min -1 . The curves obtained, as shown in Fig. 2, clearly demonstrate the strain rate sensitivity of the tensile behavior. Figure 2 : Stress-strain curves of a polyamide 6 at different strain rates. T