Investigation of damage growth by measuring the chord modulus, microhardness and macrohardness variation in ST37 steel

In this paper, using the theory of Continuum Damage Mechanic and experimental methods, damage evolution is investigated. There are various experimental and theorical methods for measuring the Damage in materials. the experimental methods can be categorized in two type: destructive methods, for example: analysis of chord modulus variation, and the non-destructive methods, for example: microhardness or macrohardness evaluation. In this paper at the first, true stress-true strain diagram of material using the simple tension test and chord modulus variation Using repetitive loading - unloading test is obtained. For measuring plastic strain, grids are etched on the tension sample by using electroetch device. And then by measuring major ellipsoid diameter on the broken sample and comparing with the preceding circle, plastic strain at various points are specified. At specified points of the sample, the microhardness and the macrohardness are measured. Using the data of these three experimental methods, the corresponding damage is evalvated and the corresponding charts are ploted. finally The evaluated damage by these three methods is compared. It’s observed, microhardness and L-U-T test have relatively similar progress, but macrohardness progress had significant difference withn these two methods. It’s also observed, average of three methods is close to microhardness method rather than two other.