Search results for "Residual stre"

Measurement of residual stresses by the hole-drilling method: General stress-strain relationship and its solution

1990

RESIDUAL STRESS ANALYSIS OF ORTHOTROPIC MATERIALS BY THE THROUGH-HOLE DRILLING METHOD

2007

The present study deals with the development and the application of the through-hole drilling method for the residual stress analysis in orthotropic materials. Through a systematic theoretical study of the stress field present on orthotropic plates with a circular hole, the relationships between the relaxed strains measured by a rectangular strain gauge rosette and the Cartesian components of the unknown residual stresses are obtained. The theoretical formulas of each influence coefficient allow the user an easy application of the method to the analysis of uniform-residual stresses on a generic homogeneous orthotropic material. Furthermore, to extend the method to the analysis of the residu…

Optimal calculation steps for the evaluation of residual stress by the incremental hole-drilling method

1999

The integral method is a suitable calculation procedure for the determination of nonuniform residual stresses by semidestructive mechanical methods such as the hole-drilling method and the ring-core method. However, the high sensitivity to strain measurement errors due to the ill conditioning of the equations has hindered its practical use. the analysis of the influence of the strain measurment error on the computed stresses carried out in the present work has showed that, given both maximum hole depth and number of total steps, the error sensitivity depends on the particular depth increment distribution used. By means of the matrix formulation, the depth increment distribution that optimiz…

In Situ Determination of the Residual Stress Field Induced by Air Oxidation, up to 1000 °C, in a 20% Cr 5% Al Ferritic Steel, by X-Ray Diffraction

1994

Residual Strength Evaluation for Aerospace Composite Structures with Large Notch Damage in MSC.Nastran SOL 700 Advanced Composite based on Alphastar …

2013

Large notch damage usually consists of failed or completely severed stiffeners or spars, or chord with failed or completely severed attached skin or web. Large notch damage results from unknown damage sources so the damage event is immediately obvious to the flight crew. The airplane must be capable of successfully completing a flight with such damage. The determinate accidental damage event is to ensure a balanced design approach in which the damage size in linked to the structural configuration. The criterion that is generally used, called the “two bay crack criterion,” states that the damage tolerant composite structure should sustain the regulatory loads with damage in skin like sharp s…

Residual Stresses in Glasses

2013

The history dependence of the glasses formed from flow-melted steady states by a sudden cessation of the shear rate $\dot\gamma$ is studied in colloidal suspensions, by molecular dynamics simulations, and mode-coupling theory. In an ideal glass, stresses relax only partially, leaving behind a finite persistent residual stress. For intermediate times, relaxation curves scale as a function of $\dot\gamma t$, even though no flow is present. The macroscopic stress evolution is connected to a length scale of residual liquefaction displayed by microscopic mean-squared displacements. The theory describes this history dependence of glasses sharing the same thermodynamic state variables, but differi…

Fracture toughness of synthesised high-performance epoxies subject to accelerated water aging

2018

Abstract The effects of water uptake on the fracture toughness of epoxy systems with high glass-transition temperatures (Tg above 170 °C) are investigated. Aging conditioning has been conducted in hot water, followed by a desorption conditioning in a room temperature dry-airborne. Water aging determines plasticisation effects and crosslink-density modifications, revealed by reductions of the Tg. It is less known how such modifications influence the material fracture toughness. In this study, Single Edge Notched Bending samples have been tested according to standards, to evaluate the KIC fracture toughness at different stages of water absorption-desorption. The characterisation has been supp…

Activation process of reversible Pd thin film hydrogen sensors

2013

Abstract Microcantilever-based thin film palladium hydrogen sensors have high selectivity and sensitivity. Reproducibility and accuracy of the sensor performance depend on the activation process of the polycrystalline palladium film deposited on the cantilever. When the hydrogen is in solid solution ( α -phase), the cantilever bending is mostly governed by the residual film stress induced by the swelling at the grain boundaries in the film. When the palladium hydride ( β -phase) starts to be formed, the cantilever undergoes a large deflection due to hydrogen absorption-induced film swelling (10% change in volume). Differences in the phase diagrams of the palladium hydride for two film thick…

Impact behaviour of flax/epoxy composite plates

2015

This paper presents an experimental investigation of the impact behaviour of flax/epoxy composite plates submitted to low-velocity transverse impact. Low energy drop-weight impact tests have been performed on two types of quasi-isotropic flax/epoxy composites, rectangularly shaped with edges lengths of 142 mm × 94 mm and 2.85 mm thick. Residual properties have been assessed by compression after impact tests. A detailed description of damage development, especially the increase of the rear face crack with respect to the impact energy is given by the microscopic observation. The influence of impact damage on the residual strength is described. A loss of 15%–30% in compression resistance was n…

On the Solid Bonding Phenomena in Linear Friction Welding and Accumulative Roll Bonding Processes: Numerical Simulation Insights

2015

Solid Bonding based welding processes allow to obtain defect free joints with low residual stress and low distortion. However, the engineering and optimization of solid bonding processes is difficult and requires a large number of time and cost consuming test trials. In this way, proper numerical models are essential tools permitting effective process design. The aim of this research was the comparison of the material process conditions during two different manufacturing processes taking advantage of the same metallurgical phenomenon, namely solid bonding. Linear Friction Welding, used to weld non-axisymmetric components and Accumulative Roll Bonding, used to increase the mechanical propert…