FATIGUE AND BARKHAUSEN EFFECT

Piezomagnetism designates a change in the magnetization of materials induced by mechanical actions such as tension or compression. The type of Barkhausen effect that occurs in this work consists of sudden, discontinuous jumps in a material’s magnetization that appear in response to smooth (continuous) stress variations. A series of strain controlled fatigue tests with an alternating sinusoidal waveform were carried out to study the relationship between the endurance limit and the Barkhausen effect. Results of fatigue tests on steel specimens exhibiting Barkhausen pulses at various stages are reported and a threshold-crossing analysis is applied to the test results. These studies show that when the fatigue limit is approached, the Barkhausen pulses become, in general, more intense in amplitude and quantity than at other stress levels. A hypothetical mechanism is proposed that relates the intensity of the Barkhausen response to the inception of micro-cracking and rearrangements of the mechanical lattice at the microscopic level.PH.D in Civil Engineering, May 201