Kevin A. Kibble

Rate-equation model for the loading-rate-dependent mechanoluminescence of SrAl2O4:Eu2+ Dy3+

The mechanoluminescence (ML) of SrAl2O4:Eu2+,Dy3+ (SAO) phosphors was monitored as a function of its instantaneous loading rate, on which it was found to be strongly dependent. The effect of the loading rate on the ML of SAO was investigated in a systematic manner using rate equations involving the loading rate term. The rate equations and the experimental data matched well. We confirmed that the ML of SAO was created by the change in load rather than by the static load, and that the loading rate determined the shape of the ML versus the time curve in the transient regime.

Numerical analysis of superplastic blow forming of Ti–6Al–4V alloys

Abstract The superplastic blow forming of a Ti–6Al–4V sheet into a cylindrical cup has been numerically analysed based on the actual forming process using ABAQUS. A detailed element type study has been performed to eliminate the element dependency in the finite element analysis. The accuracy and reliability of the proposed finite element model has been validated in comparison with experimental data. The validation proves that, there is a good agreement between the simulation and the experiment. In addition, the best prediction of the thickness distribution can be obtained using the continuum element. Furthermore, the effects of major factors such as friction coefficient and the strain rate sensitivity index upon the optimum forming pressure-time and thickness distribution of the component have been studied systematically using the proposed finite element model.

Collapse strength analysis of casing design using finite element method

Accurately predicting the ultimate collapse strength is very important in the design of casings for the oil and gas industry. For an infinitely long thick walled casing subjected to external pressure, a finite element model has been proposed to achieve a better understanding of the ultimate collapse strength of casing. Careful comparison with a series of full-scale experiments has been conducted to verify the accuracy and reliability of the finite element model. In addition, several current predictive equations for casing design have been assessed using those available test data. The validation proves that, if the material behaviour and imperfection variables are known, the ultimate collapse strength of casing can be predicted to a satisfactory degree of accuracy. Major factors, which affect the collapse strength of casing, were studied and their effects on the collapse strength of casing were summarized. Regression analysis has been conducted on the basis of finite element predictions and a new design equation for casing collapse is presented.

Burst Strength Analysis of Casing With Geometrical Imperfections

Accurately predicting the burst strength is very important in the casing design for the oil and gas industry. In this paper, finite element analysis is performed for an infinitely long thick walled casing with geometrical imperfections subjected to internal pressure. A comparison with a series of full-scale experiments was conducted to verify the accuracy and reliability of the finite element analysis. Furthermore, three predictive equations were evaluated using the test data, and the Klever equation was concluded to give the most accurate prediction of burst strength. The finite element analysis was then extended to study the effects of major factors on the casing burst strength. Results showed that the initial eccentricity and material hardening parameter had important effects on the burst strength, while the effect of the initial ovality was small.

Comparison of Aluminium Hydroxide and Magnesium Hydroxide as Flame Retardants in SEBS-Based Composites

The flame retardancy and mechanical properties of styrene-ethylene/butylene-styrene block copolymer (SEBS) based composites, containing paraffinic hydrocarbon extender oil filled SEBS (O-SEBS), blended with copolymer polypropylene (PP), and flame-retardant filler aluminium hydroxide (ATH) or magnesium hydroxide (MH) were investigated. Limiting Oxygen Index (LOI) values of both ATH and MH filled composites increased substantially as the amount of ATH and MH increased, respectively. Furthermore, the LOI values of the ATH system are higher than those of MH for the same addition level. When MH is introduced, progressively, into ATH-filled composites, and for a constant combined filler loading of 65 wt.%, LOI only decreases, when the ratio of MH to ATH exceeds 40%. Combining the two retardants, in the composites, may have a synergistic effect with respect to fire retardance. Tensile strength, up to 50 wt.% filler, and elongation at break of the composites decrease as the amount of filler increases. However, the elongation at break of the composites filled with MH is a little higher than that with ATH, but for tensile strength there is little difference between them. At filler loading greater than 50 wt.%, the tensile strength levels off but the% elongation is dramatically reduced. Introduction of MH in ATH filled composites leads to some variation in the mechanical properties of the composites. For a combined filler loading of 65 wt.%, the elongation at break increases from around 180 to 200% for a progressive increase in the ratio of MH to ATH up to 40% and there is a large increase in% elongation to around 300% when MH ratio reaches 55–60%, thereafter the% elongation falls. This effect may be linked to particle size distribution of the respective MH and ATH fillers. In contrast, there is little effect on the tensile strength. The thermogravimetric analysis (TGA) and differential TG (DTG) data show that ATH and MH increase the thermal stability of the SEBS-based composites.

Mechanical Properties and Flame Retardancy of SEBS-Based Composites Filled with Aluminium Hydroxide

The flame retardancy and mechanical properties of styrene-ethylene/butylene-styrene block copolymer (SEBS) based composites, containing SEBS blended with a paraffinic hydrocarbon extender oil, copolymer polypropylene (PP), and aluminium hydroxide (ATH) or silane coupling agent surface-treated aluminium hydroxide (m-ATH) were investigated. A maleic anhydride-grafted SEBS (MA-SEBS) was used as a polymer modifier for some composites. As the amount of ATH or m-ATH increased the flame-retardancy of the composites improved, while the tensile strength and elongation at break decreased. When the oil-filled SEBS (O-SEBS) was partially replaced by MA-SEBS, the tensile strength of the composites increased, and elongation at break decreased. Furthermore, replacing O-SEBS with MA-SEBS and treating ATH with silane coupling agent (simultaneously) improved the tensile strength of the composites by a significant margin. The phase structure of the composites was characterised using scanning electron microscopy (SEM) and this revealed that particle-matrix interfacial bonding was improved through the addition of MA-SEBS. The stability of the composites was investigated by thermogravimetric analysis (TGA).

In-situ observation and numerical simulation of crack propagation in β-Sialon ceramics

Abstract Self-reinforced β-Sialon ceramics with elongated grain structures were investigated in-situ under SEM fracture testing by using single notched three-point-bending and pre-indentation samples. The micro damage evolution and crack propagation process were directly observed. The load–deformation curve was recorded as well. Results show that the elongated β grains play an important role in the fracture process. A chain–network model was developed to simulate the crack propagation process. Numerical results were in good agreement with the experimental results, qualitatively.

Tool wear investigation whilst turning BS970‐080A15 carbon steel using TiCN‐Al2O3 CVD coated carbide tooling in gaseous and liquid nitrogen environments

Purpose – The purpose of this work is to investigate the performance of non‐contaminating metal cutting environments and investigate the associated tool chip interface conditions. The work benchmarks flood coolant characteristics and considers gaseous cutting environments as possible alternatives.Design/methodology/approach – Cutting trials were undertaken for a range of cutting environments. Flood coolant was investigated as was dry cutting, compressed air, room temperature nitrogen and liquid nitrogen environments. A range of cutting variables was measured in order to document the effect of cutting environment.Findings – The gaseous component of the liquid nitrogen environment limited the adhesion on the tool face to a region along the flank edge of the tool, shifting rake face conditions from seizure to that of sliding. Tighter chip curl, shorter contact lengths, reduced adhesion and lower feed forces are evidence that liquid nitrogen is acting as a “liquid inert barrier” beneath the chip within the to...

Numerical Study of Radiation and Temperature Phenomena for Improved Super-Plastic Sheet Metal Forming

In most super-plastic forming (SPF) investigations the focus is usually on the material aspects. In this paper the authors develop a model to improve the heat management of SPF. The model presented improved process possibilities. The improved design involves selective application of heat to the material. Final product shape can easily be controlled by accurate temperature control of the work piece. Numerical simulation has been carried out on various components including a ‘top hat shape‘ and a heat exchanger part. Simulation comparisons are made between selective heating and conventional processing, where all of the formed material is at the same temperature, and greater process efficiency of the selective heating approach is demonstrated.

Numerical and Experimental Studies on the Laser Melting of Steel Plate Surfaces

The direct impingement of laser on the surface of a platform occurs during additive layer manufacturing especially for the first layer of powder coating. As a result, thermal stresses develop due to high temperature gradients in a thin layer of the plate surface, which can result in undesired surface deformation of the steel platform used. This study investigates the residual stress profiles on a hot-rolled AISI 1015 steel plate produced by direct laser application. A three-dimensional finite element simulation model is developed which considers the laser heating process as a sequentially coupled thermal elasto-plastic problem. Experiments using optical laser scanning microscopy to obtain surface topography of the melted surface are also presented showing reasonable agreement with the simulation results. The influence of the plate thickness on the stress-depth distribution is presented.