Modelling the fracture behaviour of adhesively-bonded joints as a function of test rate

Tapered-double cantilever-beam joints were manufactured from aluminium-alloy substrates bonded together using a single-part, rubber-toughened, epoxy adhesive. The mode I fracture behaviour of the joints was investigated as a function of loading rate by conducting a series of tests at crosshead speeds ranging from 3.33 × 10−6 m/s to 13.5 m/s. Unstable (i.e. stick–slip crack) growth behaviour was observed at test rates between 0.1 m/s and 6 m/s, whilst stable crack growth occurred at both lower and higher rates of loading. The adhesive fracture energy, GIc, was estimated analytically, and the experiments were simulated numerically employing an implicit finite-volume method together with a cohesive-zone model. Good agreement was achieved between the numerical predictions, analytical results and the experimental observations over the entire range of loading rates investigated. The numerical simulations were able very readily to predict the stable crack growth which was observed, at both the slowest and highest rates of loading. However, the unstable crack propagation that was observed could only be predicted accurately when a particular rate-dependent cohesive-zone model was used. This crack-velocity dependency of GIc was also supported by the predictions of an adiabatic thermal-heating model.Deposited by bulk importAM

Validation of a fluid–structure interaction numerical model for predicting flow transients in arteries

The interaction between the flowing blood and deforming arterial wall is critical in understanding the role of hemodynamic forces such as wall shear stress (WSS) in atherosclerosis. Numerical methods have been extensively used to understand the nature of flow around atherosclerosis susceptible regions of the vascular tree in order to establish the exact role of WSS in atherosclerosis. Unfortunately, most of the numerical studies have been performed on rigid arterial geometries, which do not take into account the effect of the interaction between the flowing blood and the dynamics of the flexible arterial wall. In vivo , blood vessels are continuously deforming with every contraction and relaxation of the heart during the cardiac cycle. This paper forms the first of the two-part paper series discussing the need for fluid-structure interaction (FSI) in hemodynamic WSS analysis. The paper presents a well validated FSI based numerical model, capable of accurately predicting flow transients in arteries. The numerical model is validated using analytical solutions and experiments conducted on polyurethane mock artery, with the numerical predictions, analytical solutions and experimental data comparing very well. Numerical studies are performed using OpenFOAM, a 3D Finite Volume Method(FVM) based C++ library.Deposited by bulk impor

A combined experimental–numerical investigation of fracture of polycrystalline cubic boron nitride

Numerical modelling of a series of experimental Single Edge V-Notched Beam tests was carried out for a number of grades of polycrystalline cubic boron nitride using the finite volume method (FV) and cohesive zone model approach. The effect of notch root radius observed experimentally was reproduced numerically via a unique CZM for each material examined. It was also found that the shape of the cohesive zone model can be signiffcant, especially when the material has a relatively high fracture energy. It was also demonstrated that the experimentally observed drop in fracture toughness with increase in test rate was not explainable in terms of the system dynamics. It was found that in order to predict the experimental fracture loads for a range of loading rates, it was necessary to modify the CZM in such a way as to preserve the micro-structural length scale information of the material embedded within the CZM.Deposited by bulk impor

Arbitrary crack propagation in multi-phase materials using the finite volume method

An arbitrary crack propagation model using cell-centre nite volume based method is presented. Crack growth in an elastic solid, across an interface perpendicular to the initial crack path and into a second elastic solid is analysed. Crack initiation and the subsequent path of propagation are shown to arise naturally out of the selection of appropriate cohesive parameters. It is shown that the allowable crack propagation path is restricted by the underlying mesh. Results are presented for a number of values of interfacial strength and ratios of elastic properties between the two elastic solids. For higher values of interfacial strength, the crack is shown to propagate straight through the interface, while for lower values of interfacial strength, the crack is shown to change direction and propagate along the interface. It is shown that with careful selection of material and interface parameters it is possible to arrest a propagating crack at the interface. The method represents a useful step towards the prediction of crack propagation in complex structures.Other funderElement 6 Ltd and Enterprise IrelandDeposited by bulk importkpw7/11/1

A family of experiments on test-driven development

Context:: Test-driven development (TDD) is an agile software development approach that has been widely claimed to improve software quality. However, the extent to which TDD improves quality appears to be largely dependent upon the characteristics of the study in which it is evaluated (e.g., the research method, participant type, programming environment, etc.). The particularities of each study make the aggregation of results untenable. Objectives:: The goal of this paper is to: increase the accuracy and generalizability of the results achieved in isolated experiments on TDD, provide joint conclusions on the performance of TDD across different industrial and academic settings, and assess the extent to which the characteristics of the experiments affect the quality-related performance of TDD. Method:: We conduct a family of 12 experiments on TDD in academia and industry. We aggregate their results by means of meta-analysis. We perform exploratory analyses to identify variables impacting the quality-related performance of TDD. Results:: TDD novices achieve a slightly higher code quality with iterative test-last development (i.e., ITL, the reverse approach of TDD) than with TDD. The task being developed largely determines quality. The programming environment, the order in which TDD and ITL are applied, or the learning effects from one development approach to another do not appear to affect quality. The quality-related performance of professionals using TDD drops more than for students. We hypothesize that this may be due to their being more resistant to change and potentially less motivated than students. Conclusion:: Previous studies seem to provide conflicting results on TDD performance (i.e., positive vs. negative, respectively). We hypothesize that these conflicting results may be due to different study durations, experiment participants being unfamiliar with the TDD process, or case studies comparing the performance achieved by TDD vs. the control approach (e.g., the waterfall model), each applied to develop a different system. Further experiments with TDD experts are needed to validate these hypotheses

An Empirical Assessment on Affective Reactions of Novice Developers When Applying Test-Driven Development

We study whether and in which phase Test-Driven Development (TDD) influences affective states of novice developers in terms of pleasure, arousal, dominance, and liking. We performed a controlled experiment with 29 novice developers. Developers in the treatment group performed a development task using TDD, whereas those in the control group used a non-TDD development approach. We compared the affective reactions to the development approaches, as well as to the implementation and testing phases, exploiting a lightweight, powerful, and widely used tool, i.e., Self-Assessment Manikin. We observed that there is a difference between the two development approaches in terms of affective reactions. Therefore, it seems that affective reactions play an important role when applying TDD and their investigation could help researchers to better understand such a development approach

A family of experiments on test-driven development

Abstract Context: Test-driven development (TDD) is an agile software development approach that has been widely claimed to improve software quality. However, the extent to which TDD improves quality appears to be largely dependent upon the characteristics of the study in which it is evaluated (e.g., the research method, participant type, programming environment, etc.). The particularities of each study make the aggregation of results untenable. Objectives: The goal of this paper is to: increase the accuracy and generalizability of the results achieved in isolated experiments on TDD, provide joint conclusions on the performance of TDD across different industrial and academic settings, and assess the extent to which the characteristics of the experiments affect the quality-related performance of TDD. Method: We conduct a family of 12 experiments on TDD in academia and industry. We aggregate their results by means of meta-analysis. We perform exploratory analyses to identify variables impacting the quality-related performance of TDD. Results: TDD novices achieve a slightly higher code quality with iterative test-last development (i.e., ITL, the reverse approach of TDD) than with TDD. The task being developed largely determines quality. The programming environment, the order in which TDD and ITL are applied, or the learning effects from one development approach to another do not appear to affect quality. The quality-related performance of professionals using TDD drops more than for students. We hypothesize that this may be due to their being more resistant to change and potentially less motivated than students. Conclusion: Previous studies seem to provide conflicting results on TDD performance (i.e., positive vs. negative, respectively). We hypothesize that these conflicting results may be due to different study durations, experiment participants being unfamiliar with the TDD process, or case studies comparing the performance achieved by TDD vs. the control approach (e.g., the waterfall model), each applied to develop a different system. Further experiments with TDD experts are needed to validate these hypotheses