Piezomagnetism and fatigue

Abstract

Piezomagnetism refers to a change in the intrinsic magnetization of a material subjected to mechanical actions such as tension or compression. In a ferromagnet such as a mild steel these effects are easily measured: typically a stress of or 140 MPa induces a magnetic moment of the order of emu or , resulting in flux densities in the range 10 mG or T in the vicinity of the specimen. Since piezomagnetic effects are due to interactions between the mechanical and magnetic mesostructure of materials microplastic processes that alter the arrangement of the ferromagnetic domain structure affect the intensity of the associated magnetic fields. The progressive degradation of such materials under cyclic loading can therefore be tracked by following the evolution of the piezomagnetic field. Specifically, if the measurements are displayed as loci in a three-dimensional stress - strain - field (B) space, the approach to fatigue failure is paralleled by a series of conspicuous geometric transformations of these curves. Complementary information also appears in continuous-time records of B(t): these magnetograms clearly show the abrupt incidence of `infarcts' (microcracks) and the cumulation of phase shifts as the material degrades.

Detection of Fatigue Damage Prior Crack Initiation with Scanning SQUID Microscopy

“…The fatigue process can be detected and monitored in the earliest stages of highcycle fatigue, by the increase in dislocation density and hardness, and in the final stages, through the direct observation of initiated cracks [1][2][3]. But there are no probative, nondestructive techniques to follow incipient fatigue through the critical intermediate stage between dislocation saturation and prior to crack nucleation.…”

Exact solution for 2D polygonal inclusion problem in anisotropic magnetoelectroelastic full-, half-, and bimaterial-planes

“…Many striking features have been observed as related to the coupling among the elastic, electric, and magnetic fields, such as piezoelectric (PE), piezomagnetic (PM), magnetoelectric (ME) and magnetoelectroelastic couplings (Benveniste, 1995;Erber et al, 1997;Meeker and Dozor, 1999;Sander, 1999;Aboudi, 2001;Fiebig et al, 2002;Ryu et al, 2002;Mazumder and Battacharyya, 2003). It is particularly interesting that although magnetoelectric coupling does not exist in piezoelectric or piezomagnetic phase alone, it can be acquired in the corresponding composites, and the effect could be even larger than that in some of the single phase materials of magnetoelectricity (e.g., Nan, 1994).…”

“…It is particularly interesting that although magnetoelectric coupling does not exist in piezoelectric or piezomagnetic phase alone, it can be acquired in the corresponding composites, and the effect could be even larger than that in some of the single phase materials of magnetoelectricity (e.g., Nan, 1994). The energy conversion among elastic, electric, and magnetic forms provides numerous opportunities for potential applications of the coupling materials and structures as ultrasonic transducers, magnetic-field probes, and microdrives (Erber et al, 1997;Gibbs et al, 1997;Frank and Schilling, 1998;Meeker and Dozor, 1999;Li, 2003). In order to understand the coupling features in and among PE, PM, and ME, various analytical and numerical studies have been also carried out (Daher, 1996;Ting, 1996;Huang and Kuo, 1997;Li and Dunn, 1998;Aboudi, 2000;Li, 2000Li, , 2003Liu et al, 2001;Pan, 2001Pan, , 2002aPan and Heyliger, 2002;Chen and Lee, 2003;Ding and Jiang, 2003;Gao et al, 2003a,b;Horiguchi and Shindo, 2003;Soh et al, 2003;Wang and Zhong, 2003a,b;Pan and Han, submitted for publication).…”

Detecting damage in steel with scanning SQUID microscopy

“…Magnetic methods are particularly promising for ferromagnetic materials such as structural steels [1,2]. Parameters such as the saturation magnetization, coercivity, Barkhausen noise and magnetic hysteresis change significantly during the initial and final stages of fatigue.…”

“…First, they do not readily measure the progress of fatigue in stage 2 [2], which is the longest and, usually, the most important stage. (A part in stage 1 has most of its life left, and a part in stage 3 is, ordinarily, so close to failure that one cannot chance waiting for it to appear.)…”