NDTnet 1998 Aug, Vol.3 No.8

Abstract

Nondestructive inspection of machine parts and structural members is possible provided that the relations are known between physical properties (and among them - magnetic characteristics) being employed to this end and main parameters of the structure and mechanical properties of the metal being in service.

Dependences of the true yield stress, a and coercive force, Hc on shear strain, A beingcaused by tension and rolling, have been determined experimentally on cylindrical ironsamples. To correlate the yield strength and coercivity of iron with its grain sizes thefollowing single-type equations have been derived by the fitting tecnique: _y =₀ + K_yd_g^-0,5 and H_cy =H_co + K_m - d_g^-0,5 , where ₀=149.7 MPa, K_y =8.66 MPa mm^0.5, H_c0=1.26A/cm and K_m = 0.0048 A mm^-0.5. As a result of mathematical simulation, the correlation equations of exponential type have been obtained so as to characterize the strain hardening, d=_N+A -ⁿ, and also the increase of the coercivity because of deformation, H_cd = H_cN + B ^m, where _N=202.6 MPa, A = 270 MPa, n = 0.5, H_cN=1.67 A/cm, B = 3.72 A/cm, m = 0.371 for recrystallized iron and N=520.6 Mpa, A = 158 MPa, n = 0.43, H_cN=3.4 A/cm, B = 3.05 A/cm, m =0.046 for polygonized iron. Contributions of different factors (solid-solution and precipitation hardening) to the hardening of iron have been estimated, and also correlation of the strain hardening with the increase of dislocation density has been verified. After inversion of mentioned equations, relevant expressions for nondestructive inspection have been obtained in the form which is suitable for evaluation of the residual plastic shear strains by coercivity: = 0.032 H_c^2.576for recrystallized iron and = 3.37 10 ^-11 - H_c^21.64 for polygonized iron.It has been shown that the threshold states of metal (beginning of yielding state, threshold of steady uniform tension and strain hardening limit) are important with respect to the growth rate of the coercivity.Namely, this rate appreciably decreases beyond the threshold of uniform deformation of recrystallized iron, and parameters of relevant expression should be modified: = 0.0011 - H_c^6.11

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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