MICROCRACKS GROWTH IN PUSH-PULL AND REVERSED TORSION IN

VÉRONIQUE DOQUET; GRACIELA BERTOLINO

Grecia

Conferencia; ECF 16 - 16th European Conference of Fracture; 2006

ECF

In many metals, like stainless steel, the arrest of Stage I cracks on grain boundaries (G.Bs.) determines the endurance limit. The mechanisms of crack growth beyond a grain boundary in a globally elastic polycrystal have thus to be understood and properly modelled. In most models, the resistance of a GB to crack growth is considered overcome as soon as plasticity has been activated in the next grain, which leads to a critical resolved shear stress criterion on a potential dislocation source ahead of the blocked slip band. Either this condition is fulfilled and the crack is considered to grow immediately into the next grain or it is not and the crack is considered arrested once and for all. However, microcracks are often observed to stay arrested for a large number of cycles at GBs and then resume propagation (see below). This suggests that crack growth beyond a GB requires an incubation period after the activation of a slip system, during which a microcrack could initiate in the next grain, due to local cyclic plasticity and link with the arrested one, thus allowing further propagation. Such an incubation period was modelled by Morris et al [1] and the present authors [2]. In both cases, it was evaluated from the resolved shear stress on a potential slip system in the next grain. However, the comparison of arrest periods at GBs in push-pull and reversed torsion reported below suggest that it should rather depend on a combination of shear and opening stress on this slip system. Stress-controlled push-pull and reversed torsion tests were performed on 316LN steel specimens in the high-cycle range (2.105 to 2.106 cycles). The tests were periodically interrupted for preparation of replicas, which allowed tracing back of microcracks development (Fig.1). Microcracks initiated early (in some cases, the main crack was already present at 15% of the fatigue life) and propagated along slip bands over 1 to 5 grains, depending on the stress range and loading mode: longer Stage I cracks were observed for smaller stress ranges and push-pull led to earlier transition to stage II than reversed torsion for equivalent stress ranges. Stage I transgranular crack growth rates were less than 10 Burgers vectors/cycle and showed no clear correlation with the stress range or loading mode. Microcracks were frequently arrested for tens to hundreds thousands cycles at grain boundaries and then resumed propagation. The smaller the applied stress range, the longer the arrest periods (Fig. 2). The scatter in arrest periods increased as the stress range decreased. In reversed torsion under ��260MPa Tresca equivalent stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. cases, it was evaluated from the resolved shear stress on a potential slip system in the next grain. However, the comparison of arrest periods at GBs in push-pull and reversed torsion reported below suggest that it should rather depend on a combination of shear and opening stress on this slip system. Stress-controlled push-pull and reversed torsion tests were performed on 316LN steel specimens in the high-cycle range (2.105 to 2.106 cycles). The tests were periodically interrupted for preparation of replicas, which allowed tracing back of microcracks development (Fig.1). Microcracks initiated early (in some cases, the main crack was already present at 15% of the fatigue life) and propagated along slip bands over 1 to 5 grains, depending on the stress range and loading mode: longer Stage I cracks were observed for smaller stress ranges and push-pull led to earlier transition to stage II than reversed torsion for equivalent stress ranges. Stage I transgranular crack growth rates were less than 10 Burgers vectors/cycle and showed no clear correlation with the stress range or loading mode. Microcracks were frequently arrested for tens to hundreds thousands cycles at grain boundaries and then resumed propagation. The smaller the applied stress range, the longer the arrest periods (Fig. 2). The scatter in arrest periods increased as the stress range decreased. In reversed torsion under ��260MPa Tresca equivalent stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. cases, it was evaluated from the resolved shear stress on a potential slip system in the next grain. However, the comparison of arrest periods at GBs in push-pull and reversed torsion reported below suggest that it should rather depend on a combination of shear and opening stress on this slip system. Stress-controlled push-pull and reversed torsion tests were performed on 316LN steel specimens in the high-cycle range (2.105 to 2.106 cycles). The tests were periodically interrupted for preparation of replicas, which allowed tracing back of microcracks development (Fig.1). Microcracks initiated early (in some cases, the main crack was already present at 15% of the fatigue life) and propagated along slip bands over 1 to 5 grains, depending on the stress range and loading mode: longer Stage I cracks were observed for smaller stress ranges and push-pull led to earlier transition to stage II than reversed torsion for equivalent stress ranges. Stage I transgranular crack growth rates were less than 10 Burgers vectors/cycle and showed no clear correlation with the stress range or loading mode. Microcracks were frequently arrested for tens to hundreds thousands cycles at grain boundaries and then resumed propagation. The smaller the applied stress range, the longer the arrest periods (Fig. 2). The scatter in arrest periods increased as the stress range decreased. In reversed torsion under ��260MPa Tresca equivalent stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. cases, it was evaluated from the resolved shear stress on a potential slip system in the next grain. However, the comparison of arrest periods at GBs in push-pull and reversed torsion reported below suggest that it should rather depend on a combination of shear and opening stress on this slip system. Stress-controlled push-pull and reversed torsion tests were performed on 316LN steel specimens in the high-cycle range (2.105 to 2.106 cycles). The tests were periodically interrupted for preparation of replicas, which allowed tracing back of microcracks development (Fig.1). Microcracks initiated early (in some cases, the main crack was already present at 15% of the fatigue life) and propagated along slip bands over 1 to 5 grains, depending on the stress range and loading mode: longer Stage I cracks were observed for smaller stress ranges and push-pull led to earlier transition to stage II than reversed torsion for equivalent stress ranges. Stage I transgranular crack growth rates were less than 10 Burgers vectors/cycle and showed no clear correlation with the stress range or loading mode. Microcracks were frequently arrested for tens to hundreds thousands cycles at grain boundaries and then resumed propagation. The smaller the applied stress range, the longer the arrest periods (Fig. 2). The scatter in arrest periods increased as the stress range decreased. In reversed torsion under ��260MPa Tresca equivalent stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. et al [1] and the present authors [2]. In both cases, it was evaluated from the resolved shear stress on a potential slip system in the next grain. However, the comparison of arrest periods at GBs in push-pull and reversed torsion reported below suggest that it should rather depend on a combination of shear and opening stress on this slip system. Stress-controlled push-pull and reversed torsion tests were performed on 316LN steel specimens in the high-cycle range (2.105 to 2.106 cycles). The tests were periodically interrupted for preparation of replicas, which allowed tracing back of microcracks development (Fig.1). Microcracks initiated early (in some cases, the main crack was already present at 15% of the fatigue life) and propagated along slip bands over 1 to 5 grains, depending on the stress range and loading mode: longer Stage I cracks were observed for smaller stress ranges and push-pull led to earlier transition to stage II than reversed torsion for equivalent stress ranges. Stage I transgranular crack growth rates were less than 10 Burgers vectors/cycle and showed no clear correlation with the stress range or loading mode. Microcracks were frequently arrested for tens to hundreds thousands cycles at grain boundaries and then resumed propagation. The smaller the applied stress range, the longer the arrest periods (Fig. 2). The scatter in arrest periods increased as the stress range decreased. In reversed torsion under ��260MPa Tresca equivalent stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. stress range, arrest periods up to 105 cycles were observed at some G.Bs, while for a smaller equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. tests in torsion are in progress to document this point. equivalent stress range (��215MPa), arrest periods do not exceed 4.104 cycles, in push-pull. Further tests in torsion are in progress to document this point. tests in torsion are in progress to d