Fatigue crack surface area and crack front length: new ways to look at fatigue crack growth

This paper discusses the appropriateness of crack length as a reference dimension for fatigue damage. Current discussion on short crack versus long crack data is still divided between various approaches to model small crack growth. A proper physical explanation of the probable cause of the apparent differences between short crack and long crack data is not yet provided. Long crack data often comprises crack growth in constant thickness specimens, with a through crack of near constant crack front geometry. This is not true for corner cracks or elliptical surface crack geometries in the small crack regime where the crack front geometry is not symmetric or through-thickness. This affects similitude parameters that are based on the crack length. The hypothesis in this paper is that a comparison between long crack data and short crack data should be made using similar increments in crack surface area. The work applied to the specimen is dissipated in generation of fracture surface, whereas fracture length is a result. The crack surface area approach includes the two-dimensional effect of crack growth geometry in the small crack regime. A corner crack and a through crack are shown to follow the same power law relationship when using the crack area as base parameter. The crack front length is not constant, and its power law behaviour for a corner crack is shown

Matlab code and dataset for the spectral characteristics of gold nanoparticle doped optical fibre

The peroid number of the gold nanoparticle doped optical fibre with different gauge lengths (0.1069cm, 0.5345cm, 1.0690cm and 2.1379cm) are generated in the dataset. The spectral characteristics from the dataset can be illustrated by the given matlab code.</p

An experimental investigation into pin loading effects on fatigue crack growth in Fibre Metal Laminates

AbstractThis paper provides an experimental investigation into the pin loading effects on the crack growth behaviour in Fibre Metal Laminates. The pin loading effects and bypass loading effects are incorporated in two different tested joints. The analysis of the test results shows that pin loading dominates the crack growth only in the vicinity of the pin hole and the superposition method for analysing stress intensity factor in FMLs with pin loading effects can be applied

Matlab code and dataset for the spectral characteristics of gold nanoparticle doped optical fibre

The peroid number of the gold nanoparticle doped optical fibre with different gauge lengths (0.1069cm, 0.5345cm, 1.0690cm and 2.1379cm) are generated in the dataset. The spectral characteristics from the dataset can be illustrated by the given matlab code.</p

Data underlying the article: Early fatigue damage accumulation of CFRP Cross-Ply laminates considering size and stress level effects

Ply-block size and stress level effect on accumulation of transverse cracks and delamination are investigated during early fatigue life of CFRP laminates. Tension-tension fatigue tests under different stress levels were performed for two cross-ply configurations. Edge observation with digital cameras, digital image correlation and acoustic emission were employed for in-situ damage monitoring. Transverse cracks were dominant for [0/902]s laminates with almost non-existent delamination, while different interactive levels between both damage mechanisms occurred for [02/904]s laminates. Poisson’s ratio identifies whether early fatigue damage is dominant by transverse cracks or involves delamination. Cumulative AE energy is a helpful indicator of crack density.</p

Composite specimens under fatigue and impact loading conditions

Open-hole specimens were subjected to constant amplitude fatigue loading up to failure while in-situ impact and manufacturing imperfections were used so as to demonstrate unexpected phenomena. Acoustic emission and digital image correlation techniques were employed in order to collect condition monitoring data which were used for the training and testing processes.Eight specimens were used for the training process, and they were subjected only to fatigue loading. Four specimens were used for testing the proposed adaptive model. Three of them were subjected to fatigue and in-situ impact, and created a left, a right outlier and an inlier performer respectively to the training specimens. The last one was subjected just to fatigue loading but created one more left outlier case since it had a manufacturing imperfection

Simulation of Ultrasonic Beam Propagation From Phased Arrays in Anisotropic Media Using Linearly Phased Multi-Gaussian Beams

Phased array ultrasonic testing is widely used to test structures for flaws due to its ability to produce steered and focused beams. The inherent anisotropic nature of some materials, however, leads to skewing and distortion of the phased array beam and consequently measurement errors. To overcome this, a quantitative model of phased array beam propagation in such materials is required, so as to accurately model the skew and the distortion. The existing phased array beam models which are based on exact methods or numerical methods are computationally expensive or time consuming. This article proposes a modeling approach based on developing the linear phased multi-Gaussian beam (MGB) approach to model beam steering in anisotropic media. MGBs have the advantages of being computationally inexpensive and remaining non-singular. This article provides a comparison of the beam propagation modeled by the developed ordinary Gaussian beam and linear phased Gaussian beam models through transversely isotropic austenitic steel for different steering angles. It is shown that the linear phased Gaussian beam model outperforms the ordinary one, especially at steering angles higher than 20° in anisotropic solids. The proposed model allows us to model the beam propagation from phased arrays in both isotropic and anisotropic media in a way that is computationally inexpensive. As a further step, the developed model has been validated against a finite element model (FEM) computed using COMSOL Multiphysics.status: publishe

Evaluation of the mechanical performance of a composite multi-cell tank for cryogenic storage: part II - experimental assessment

Cryogenic fuel containment at tank configurations that can conform to a prescribed space is of significant importance for hypersonic aircrafts. To ensure a safe flight, continuous monitoring of temperature, strain and damage initiation/propagation of the tank is crucial. The possibilities to perform these tasks are strongly dependent on the way the tank itself is designed and manufactured. Therefore, the study presented here focuses on both the analysis and full experimental evaluation of an innovative multi-spherical composite-overwrapped pressure vessel under hydrostatic testing at ambient conditions and pressure cycling with a cryogenic medium (LN2). The tested tank (scaled to 44 [l]) consists of four partly merged quasi isotropically reinforced spherical cells, where the intersections are strengthened by additional UD straps; the central cylindrical cavity is reinforced by an inserted hollow tube (aluminum). The design is characterized by the equal shell strain principle between the spheres and sphere connecting areas (intersections). During hydro-burst testing at a high displacement rate, the strain and damage progression was monitored with Digital-ImageCorrelation (DIC) and Acoustic Emission (AE) techniques. The effect of LN2 filling, pressure cycling and draining on the composite overwrap temperature gradient and related strains was additionally obtained with Fiber Bragg Gratings (FBGs) and thermocouples. The findings of this study were compared to a FEM-based thermo-mechanical model coupled with a progressive failure analysis (PFA) as presented in part I of this study (FE) [14]. The results of the hydrostatic tests completely verified the analytical and FE-based equal strain design principle where the predicted failure took place at the vicinity of the hollow center tube in a leak-before-burst sequence. In addition, stress-strain measurements in the cryogenic regime verified the suitability of the involved stiffness and CTE fitting functions (FE model). As a general conclusion, the most important finding here is the absence of damage in the composite shell; this may be regarded as a positive indication about the suitability of conformal Type IV multi-spherical COPVs for cryogenic storage. It is however believed that a careful consideration of the temperature-dependent strain field remains a critical parameter. Ideally, this strain field should be as homogeneous as possible to avoid CTE induced stress concentrations