No abstract

Dimensionless stress intensity factors were determined for single-edge-crack solid and hollow round bars loaded in tension. These factors were calculated from experimental compliance (inverse slope of load-displacement curve) measurements made over a range of dimensionless crack depths (lengths) from 0.05 to 0.65. The tests were made with 76-mm (3-in.) diameter solid and hollow round bars notched on one side and loaded in axial tension. The hollow bar had an inner to outer diameter ratio of 0.33. A comparison was made with data in the literature for rectangular bars; for a crack depth to diameter ratio of 0.0001 the dimensionless stress intensity factor for a solid round bar is 0.55 compared with 2.0 for a rectangular bar.

Fatigue crack growth at intermediate rates was measured in compact tension specimens of the microstructurally contrasting alloys Ti-6Al-4V (Imperial Metal Industries, Ltd. [IMI] titanium 318) and Ti-6Al-5Zr-0.5Mo-0.25Si (IMI titanium 685). Sinusoidal loading was used with a ratio of minimum load to maximum load R of 0.1. The incidence of crack closure was examined during fatigue with both direct current potential drop and crack-opening-displacement (COD) methods; COD was found to be more reliable for closure measurement than potential drop. In contract to the fine-grained IMI 318, the coarse-structured IMI 685 showed substantial load transfer across the crack faces during fatigue and this was attributed to mismatch of the fracture faces. It was shown that the large differences in crack growth rate between the two alloys could be substantially accounted for by an effective stress intensity factor range concept. Marked reductions in growth rate produced by variable amplitude loading of the IMI 318 could not be explained in terms of crack closure.

Standard Charpy calibration specimens designed for verification of pendulum impact machines have been tested on a vertical drop tower impact machine. Two different test techniques (optical velocity measurement and integrated digital load-time response) for measuring the fracture energy of these specimens have produced equivalent sets of data which match the range of expected pendulum machine results. The more flexible vertical drop tower machine can therefore be used to measure Charpy impact energies with the same reliability as the conventional pendulum machines.

The Top-on ultrasonic method proposed earlier was applied to the rising load KIscc testing and the validity was confirmed by comparing the determined KIscc values with those measured according to the conventional longtime KIscc testing in the same environments. In addition, the influences of loading rate, fatigue precracking stress intensity level, and fracture morphology of fatigue precracked zone on KIscc were discussed.