Rezwanul Haque

Feasibility of measuring residual stress profile in different self-pierce riveted joints

Abstract The feasibility of measuring residual stresses in self-pierce riveted (SPR) joints by neutron diffraction technique was investigated. The main challenge involved dealing with the very small dimensions of SPR joints. Two different joints were examined: aluminium–steel and steel–steel. Even though small dimensions were involved, meaningful results were obtained. In the rivet head, tensile stress was observed for the steel–steel sample, whereas only compressive stress was observed for the aluminium–steel. The residual stress in the rivet head was higher at the centre and lower at the edge for both joints. Stresses in the sheet material beside the rivet wall and at a distance of three times the rivet radius from the rivet axis were not significant. For the SPR joints examined, the maximum value of residual stress was compressive and occurred in the rivet leg. The results are discussed according to the physical events involved during the process.

Characterisation of force–displacement curve in self-pierce riveting

Abstract A systematic study of the force–displacement curve of the self-piercing riveting (SPR) process and associated sample characterisation have been carried out in this work. Carbon steel sheet with three different thicknesses and steel rivets with three different hardness levels have been used to examine their impact on the force–displacement characteristic curve. The force–displacement curve is segmented into four different stages, which give the signature of the quality of the joint depending on different process variables. This study shows that the force–displacement curve can be used to monitor the quality of the joint within the same process parameters (rivet length and hardness, total stack thickness and die geometry).

Optimising parameters for meaningful measurement of residual strain by neutron diffraction in self-pierce riveted joints

Abstract The aim of this work is to examine the uncertainties involved in measuring residual strain and their dependence on both the gauge volume of the neutron beam and the acquisition time in self-pierce riveted (SPR) joints while using the neutron diffraction technique. The main challenge involved dealing with the very small dimensions of SPR joints and developing optimum instrument configuration that allowed faster and/or more accurate stress measurement in SPR while maintaining the same time resolution required for the millimetre scale of the problem. Two different gauge volumes were used (0·125 and 1·0 mm3), and two different measuring directions were chosen in order to examine the rotational accuracy of the sample table. All measurements were conducted in steel‐steel joints. Even though small sizes were involved, meaningful results were obtained and measurement errors were reduced by optimising the instrument parameters.

Residual stress profiles in riveted joints of steel sheets

Abstract The residual stress profiles in two different self-piercing riveted (SPR) joints were characterised using the neutron diffraction technique. The joints were produced using semi-tubular steel rivets and carbon steel sheets of different thicknesses and hardnesses. The residual stress in the sheet material inside the bore of the rivet was compressive at the centre and the stress became tensile away from the centre. The stresses found in the semi-tubular rivet were compressive, with a lower magnitude in the rivet head compared with those in the rivet leg. For the SPR joints examined, the compressive residual stress in the rivet leg was greater for the thin joint than the thick joint, and this was due to the higher force gradient encountered during the rivet flaring stage. The originality of this work was to relate the residual stress profile to the physical event that occurred during the SPR process.

Evaluation of Residual Stress in SPR Joint by Neutron Diffraction

The feasibility of measuring residual stresses in Self-Pierce Riveted (SPR) joints by neutron diffraction was evaluated in this study. Despite the small dimensions involved, meaningful results were obtained. It was observed that residual stress in the rivet head was higher in the centre and lower at the edge. For the SPR joints examined, the maximum value of residual stress evaluated was 550MPa, compressive and occurred in the rivet leg. Stresses in material adjacent to the rivet wall and at a distance of three times the rivet radius from the rivet axis were not significant. The results are discussed with respect to the physical events involved during SPR.

SPR Characteristics Curve and Distribution of Residual Stress in Self-Piercing Riveted Joints of Steel Sheets

Neutron diffraction was used to describe the residual stress distributions in self-piercing riveted (SPR) joints. The sheet material displayed a compressive residual stress near the joint, and the stress gradually became tensile in the sheet material far away from the joint. The stress in the rivet leg was lower in the thick joint of the softer steel sheet than in the thin joint of the harder steel sheet. This lower magnitude was attributed to the lower force gradient during the rivet flaring stage of the SPR process curve. This study shows how the residual stress results may be related to the physical occurrences that happened during joining, using the characteristics curve. The study also shows that neutron diffraction technique enabled a crack in the rivet tip to be detected which was not apparent from a cross-section.

Failure Analysis of Boat Rudder Fitting Fabricated from a Type 304 Stainless Steel

The failure of a type 304 stainless steel component subassembled by welding and used on a boat in a marine environment was investigated. The mechanism of damage initiation and the cause of final failure were investigated. Initial examination of the component indicated deep branching cracks that were thought to have developed during service. The combination of microhardness test and finite element modeling (FEM) was employed to probe micromechanical properties of the damaged area. The corrosion observed was followed with scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). FEM analysis suggests that the cracked area had been subjected to tensile stresses in service. Microhardness across the welded section did not show any mechanical degradation across the weld and heat-affected zone. The cracked area was evidently corroded, and the microanalysis in the SEM/EDS indicated the presence of corrosion products. Regions around the cracks especially at the root of the crack were found to be severely depleted of Ni. It is evident that the primary course of failure was from the cracking from SCC attack and that the pitting observed is a secondary effect in the cracked region.