The Feasibility of Estimating Elastic-Plastic Strain in Powder Structural Steel with Different Residual Porosity by Magnetic Methods
The world’s output of products made of sintered powders is constantly growing due to high productivity and efficiency of powder metallurgy processe s. Safe operation of machine parts and structural components made of sintered powder ma t ials calls for reliable methods of nondestructive testing. The paper presents a procedure of t wo-parameter testing of product structure and porosity, as well as results of investigatio ns into the effect of tensile stresses on the magnetic characteristics of powder structural stee with different residual porosity; it also discusses the applicability of the results for estimat ing elastic-plastic strains.
Correlation between the stress-strain state parameters and magnetic characteristics of carbon steels
A method for reconstruction of the stress-strain diagrams of steel objects from their magnetic characteristics determined directly during tension has been suggested. The coercive force, residual induction in the major hysteresis loops, and the maximum magnetic permeability are recommended as parameters for nondestructive testing of stresses and strains.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.