A review of the wire arc additive manufacturing of metals: properties, defects and quality improvement

http://doras.dcu.ie/17607/1/Review_of_residual_stresses-Final.pdf

Methods of measuring residual stresses in components

A technique is described for the measurement of the residual stress tensor averaged over a specified volume within a component. The method involves measurement of small changes in lattice spacing using high resolution neutron diffraction. The stress is inferred from these measurements of the strain, and the theory of the relationship between the two quantities is described, including the effects of crystalline anisotropy. The various types of high resolution neutron diffractometer suitable for the work are described. Experimental results validating the method are given for a simple bent bar of mild steel of known strain, a plastically strained mild steel bar, and a mild steel tube of known torsional strain. Examples of the method in practical use are given by a cracked fatigue test specimen, a double-V test weld and a weld joining a tube to a plate. A more detailed example is the anisotropic response of a polycrystalline sample under elastic and plastic strain; this is illustrated by measurements...

Neutron diffraction methods for the study of residual stress fields

In 1903, Alexander Graham Bell developed a design principle to generate lightweight, mechanically robust lattice structures based on triangular cells; this has since found broad application in lightweight design. Over one hundred years later, the same principle is being used in the fabrication of nanolattice materials, namely lattice structures composed of nanoscale constituents. Taking advantage of the size-dependent properties typical of nanoparticles, nanowires, and thin films, nanolattices redefine the limits of the accessible material-property space throughout different disciplines. Herein, the exceptional mechanical performance of nanolattices, including their ultrahigh strength, damage tolerance, and stiffness, are reviewed, and their potential for multifunctional applications beyond mechanics is examined. The efficient integration of architecture and size-affected properties is key to further develop nanolattices. The introduction of a hierarchical architecture is an effective tool in enhancing mechanical properties, and the eventual goal of nanolattice design may be to replicate the intricate hierarchies and functionalities observed in biological materials. Additive manufacturing and self-assembly techniques enable lattice design at the nanoscale; the scaling-up of nanolattice fabrication is currently the major challenge to their widespread use in technological applications.

Nanolattices: An Emerging Class of Mechanical Metamaterials.

Microstructure and residual stress improvement in wire and arc additively manufactured parts through high-pressure rolling

Residual stress modification by post-weld treatment and its beneficial effect on fatigue strength of welded structures

COMMITTEE MANDATE Concern for crack initiation and growth under cyclic loading as well as unstable crack propagation and tearing in ship and offshore structures. Due attention shall be paid to practical application and statistical description of fracture control methods in design, fabrication and service. Consideration is to be given to the suitability and uncertainty of physical models. The work shall be coordinated with that of Committee V.2.

Fatigue and Fracture

Enhancement of the fatigue resistance of welded transverse stiffeners and cover plate details by ultrasonic impact treatment (UIT) was evaluated in 18 full-scale W27×129 rolled beam specimens. Fatigue tests were conducted under constant amplitude loading at various stress range levels and at two minimum stress levels simulating the effect of sustained load. The test specimens were investigated for fatigue crack initiation and propagation. Distributions of residual stresses adjacent to the weld toe were determined before and after the treatment. Test results indicated that UIT enhanced the fatigue performance of all treated details by improving the weld toe profile, changing microstructure and introducing beneficial compressive residual stresses at the treated weld toe. The treatment effectively elevated the fatigue crack growth threshold and the fatigue limit without changing the slope of the S–N curve.

Fatigue Resistance of Welded Details Enhanced By Ultrasonic Impact Treatment (UIT)

Fatigue resistance of welded details enhanced by ultrasonic impact treatment (UIT)

This report documents the results of a comprehensive experimental and analytical study that evaluated fatigue performance of several critical welded connections in the highway sign, signal and high-level luminaire support structures. In this study, infinite life fatigue resistance of connection details in the existing inventory was established and new cost-effective fatigue resistant connections were developed. About 80 full size galvanized specimens of sign, signal and high-level luminaire support structures containing different welded connections were fatigue tested. Using parametric Finite Element Analyses (FEA) of 3D models verified by test data, fatigue performance of the connections in both finite and infinite life regimes were defined in terms of fatigue stress concentration factors over the range of applicable geometric dimensions. The study demonstrated that tube-to-transverse plate connections are the most fatigue critical details in the subject structures. Increasing the stiffness of the transverse plate is the most cost-effective means of improving fatigue resistance of this connection. Groove welded connections with smaller opening in the plate exhibits largest fatigue resistance. Sharper bend radius and less number of sides reduce fatigue threshold of connections in multi-sided sections. Based on these research findings, new specification recommendations were proposed for revision to the existing AASHTO specifications.

Sougata Roy

Papers

Residual stress modification by post-weld treatment and its beneficial effect on fatigue strength of welded structures

Fatigue and Fracture

Fatigue Resistance of Welded Details Enhanced By Ultrasonic Impact Treatment (UIT)

Fatigue resistance of welded details enhanced by ultrasonic impact treatment (UIT)

Cost-Effective Connection Details for Highway Sign, Luminaire, and Traffic Signal Structures