Advances in Neutron Diffraction for Engineering Residual Stress Measurements

Abstract

The increasing awareness amongst engineers and designers, of the significance of residual stresses in influencing the useful lifetimes ofengineering components, has resulted in more demanding expectations being placed on the methods used to obtain these stresses. The neutron diffraction technique is emerging as the most attractive measuring method as the residual stresses can usually be obtained non-destructively to depths of up to 40 mm in some common engineering materials. Although it is a relatively new technique it has been used to measure the residual stresses in a range of engineering materials introduced by a wide variety of manufacturing processes such as welding, quenching, machining, shot peening, cold hole expansion and autofrettage.In this paper the neutron diffraction technique for non-destructive residual stress measurements will be described including methods used to validate the measurements. Precautions that should be taken in order to obtain reliable measurements are outlined. Procedures being investigated in order to produce a code of practice will be presented.A representative selection of stress distributions developed by a range of manufacturing processes is examined. Some comparisons are made with strain gauge, X-ray and numerical predictions. It is shown how the results can be of benefit in engineering stress analysis.

Measuring Residual Strain and Stress in Thermal Spray Coatings Using Neutron Diffractometers

“…Usually, steep strain gradients occur at surface or at interfaces and the test requires the gauge volume to be partially submerged [43]. It is to be appreciated that by using through thickness vertical scanning technique, potential errors in strain, caused by partial filling of the gauge volume introducing a geometric shift in the diffraction peak position (pseudo-strains) can be avoided [6].…”

Measuring Residual Strain and Stress in Thermal Spray Coatings Using Neutron Diffractometers

“…Usually, steep strain gradients occur at surface or at interfaces and the test requires the gauge volume to be partially submerged [37]. It is to be appreciated that by using through thickness vertical scanning technique, potential errors in strain, caused by partial filling of the gauge volume introducing a geometric shift in the diffraction peak position (pseudo-strains) can be avoided [6].…”

Neutron and X-ray diffraction study of residual and internal stress evolution in pearlitic steel during cold drawing

“…Assuming a principal (micro) strain and stress state, i.e. negligible shear stresses, the axial stress component was calculated from generalized Hooke's law as follows [16]:…”