Void nucleation and growth from heterophases and the exploitation of new toughening mechanisms in metals

Heterophases, such as precipitates, inclusions, second phases, or reinforcement particles, often drive void nucleation due to local incompatibilities in stresses/strains. This results in a significant life-limiting condition, as voids or their coalescence can lead to microcracks that reduce the ductility and fatigue life of engineering components. Continuum-mechanics-based analytical models have historically gained momentum due to their relative ease in predicting failure strain. The momentum of such treatment has far outpaced the development of theories at the atomic and micron scales, resulting in an insufficient understanding of the physical processes of void nucleation and growth. Evidence from the recent developments in void growth theories indicates that the evolution of voids is intrinsically linked to dislocation activity at the void–matrix interface. This physical growth mechanism opens up a new methodology for improving mechanical properties using hydrostatic pressurization. According to the limited literature, with a hydrostatic pressure close to 1 GPa, aluminium matrix composites can be made 70 times more ductile. This significant ductility enhancement arises from the formation of dislocation shells that encapsulate the heterophases and inhibit the void growth and coalescence. With further investigations into the underlying theories and developments of methods for industrial implementations, hydrostatic pressurization has the potential to evolve into an effective new method for improving the ductility and fatigue life of engineering components with further development

Improving interinstitutional and intertechnology consistency of pulmonary SBRT by dose prescription to the mean internal target volume dose.

Dose, fractionation, normalization and the dose profile inside the target volume vary substantially in pulmonary stereotactic body radiotherapy (SBRT) between different institutions and SBRT technologies. Published planning studies have shown large variations of the mean dose in planning target volume (PTV) and gross tumor volume (GTV) or internal target volume (ITV) when dose prescription is performed to the PTV covering isodose. This planning study investigated whether dose prescription to the mean dose of the ITV improves consistency in pulmonary SBRT dose distributions. This was a multi-institutional planning study by the German Society of Radiation Oncology (DEGRO) working group Radiosurgery and Stereotactic Radiotherapy. CT images and structures of ITV, PTV and all relevant organs at risk (OAR) for two patients with early stage non-small cell lung cancer (NSCLC) were distributed to all participating institutions. Each institute created a treatment plan with the technique commonly used in the institute for lung SBRT. The specified dose fractionation was 3 × 21.5 Gy normalized to the mean ITV dose. Additional dose objectives for target volumes and OAR were provided. In all, 52 plans from 25 institutions were included in this analysis: 8 robotic radiosurgery (RRS), 34 intensity-modulated (MOD), and 10 3D-conformal (3D) radiation therapy plans. The distribution of the mean dose in the PTV did not differ significantly between the two patients (median 56.9 Gy vs 56.6 Gy). There was only a small difference between the techniques, with RRS having the lowest mean PTV dose with a median of 55.9 Gy followed by MOD plans with 56.7 Gy and 3D plans with 57.4 Gy having the highest. For the different organs at risk no significant difference between the techniques could be found. This planning study pointed out that multiparameter dose prescription including normalization on the mean ITV dose in combination with detailed objectives for the PTV and ITV achieve consistent dose distributions for peripheral lung tumors in combination with an ITV concept between different delivery techniques and across institutions

Optimization of Surface Properties of Shot Peened TI6AL4V Alloy

As an important surface treatment method, shot peening (SP) is widely used in automotive and aerospace industries in order to improve surface properties. In the present study SP was performed on the α-β titanium alloy Ti6Al4V under various parameters (particle impingement angle, particle acceleration pressure and particle size) by using a specially designed shot peening test rig. It is aimed to optimize surface roughness and hardness of the shot peened Ti6Al4V alloy under various parameters. In order to achieve this goal shot peened samples were investigated in detail by using a non-contact laser optical profilometer and surface hardness of the samples was measured by using a micro-hardness instrument. The surface roughness values, 3D surface morphologies and micro-hardness of the samples were obtained and examined. The results show that particle impingement angle, particle acceleration pressure and particle size dramatically affect the surface properties of the Ti6Al4V alloy

Investigation of the Effects of Erosion Test Parameters on the Particle Impengement Velocity by Using CFD Analysis

Particle impingement velocity is one of the most important parameters in solid particle erosion. Particle impingement velocity depends on erosion test parameters such as particle acceleration pressure, erodent particle size and standoff distance. Over the past decades many experimental studies have been conducted to examine the effects of these parameters on the particle impingement velocity. In this study, the effects of particle acceleration pressure, erodent particle size and standoff distance on the particle impingement velocity have been investigated by using a computational fluid dynamics (CFD) program, FLUENT. In order to achieve these goals solid particle erosion tests are simulated under various test parameters and the effects of these parameters are examined in detail. The effect of particle velocity on the flow field is characterized with method geometrics. Two-dimensional plane symmetrical models are utilized to reduce the computation time. Plots of gas pressure and particle velocity contours at the XY symmetrical plane from nozzle inlet to substrate were given. CFD analysis showed that all erosion test parameters have dramatically affected particle impingement velocity. Particle impingement velocity was increased with increases in acceleration pressure while it was decreased with increases in both erodent particle size and standoff distance

Mechanical and Thermal Properties of Pumice Powder Filled PPS Composites

Recently, it is common application to use particle materials as fillers to improve engineering properties and lower the cost of finished product. Pumice powder is cheaper than most of traditional particle fillers, however use of pumice powders as a reinforcing material in composites has not been studied in literature. Hence, in this study we have investigated the mechanical and the thermal properties of pumice powder filled polyphenylenesulphide (PPS) composites. PPS composites were reinforced with pumice powder at different loading rates (0, 1, 3.5, and 10 wt%) and they were manufactured by twin screw extruder and injection molding machine. Thermal properties were investigated by thermogravimetric analysis and differential scanning calorimeter methods. Moreover, mechanical properties such as barcol hardness, tensile strength, and modulus of samples were investigated. Thermal properties of composite samples have varied significantly depending on the loading rate. Also mechanical properties of pumice powder filled PPS composites have showed better results than pure PPS. According to test results both of mechanical and thermal properties of composites have improved with pumice powder reinforcement and it is determined that pumice powders can be used instead of traditional particle fillers

Influences of Particle Impingement Angle and Velocity on Surface Roughness, Erosion Rate, and 3D Surface Morphology of Solid Particle Eroded Ti6Al4V Alloy

In this study, it is aimed to investigate the effects of particle impingement angle and velocity on the surface roughness, erosion rate, and surface morphology of solid particle eroded Ti6Al4V alloy. Ti6Al4V samples were eroded in erosion test rig under various particle impingement angles (15°, 30°, 45°, 60°, 75° and 90°) and impingement velocities (33 m/s, 50 m/s, and 75 m/s) by using 120 mesh garnet erodent particles. Subsequently, erosion rates and surface roughness values of samples were analyzed and calculated as a function of particle impingement angle and velocity. Moreover, 3D surface morphologies of the eroded samples were prepared by using high definition scanner and image processing programs. Results show that erosion rates, surface roughness values and surface morphologies of Ti6Al4V alloy have been varied significantly depending on the both particle impingement angle and velocity. Erosion rates of Ti6Al4V alloy were decreased with increases in particle impingement angle; on the other hand, the surface roughness values were increased with increases in particle impingement angle. Both erosion rates and surface roughness values were increased with increases in particle impingement velocity. Finally, the surface morphologies of the eroded samples were evaluated deeply. It is concluded that the surface morphology variation of the Ti6Al4V alloy depending on the particle impingement angle and velocity were well correlated with the erosion rates and the surface roughness values

ACTA PHYSICA POLONICA A Mechanical and Thermal Properties of Pumice Powder Filled PPS Composites

Recently, it is common application to use particle materials as llers to improve engineering properties and lower the cost of nished product. Pumice powder is cheaper than most of traditional particle llers, however use of pumice powders as a reinforcing material in composites has not been studied in literature. Hence, in this study we have investigated the mechanical and the thermal properties of pumice powder lled polyphenylenesulphide (PPS) composites. PPS composites were reinforced with pumice powder at dierent loading rates (0, 1, 3.5, and 10 wt%) and they were manufactured by twin screw extruder and injection molding machine. Thermal properties were investigated by thermogravimetric analysis and dierential scanning calorimeter methods. Moreover, mechanical properties such as barcol hardness, tensile strength, and modulus of samples were investigated. Thermal properties of composite samples have varied signicantly depending on the loading rate. Also mechanical properties of pumice powder lled PPS composites have showed better results than pure PPS. According to test results both of mechanical and thermal properties of composites have improved with pumice powder reinforcement and it is determined that pumice powders can be used instead of traditional particle llers

Effect of Particle Impact Angle, Erodent Particle Size and Acceleration Pressure on the Solid Particle Erosion Behavior of 3003 Aluminum Alloy

This study aims to examine solid particle erosion behavior of 3003 aluminum alloy. 3003 aluminum alloy samples were eroded in erosion test rig under various particle impingement angles (15°, 30°, 45° and 60°) and acceleration pressures (1.5, 3 and 4 bar) by using 80 mesh and 180 mesh sized erodent particles (garnet). The erosion rates of aluminum alloy samples were calculated depending on the erosion parameters. The erosion rates of the samples have varied dramatically depending on particle impingement angle, acceleration pressure and erodent particle size. The maximum erosion rates were observed at 15° impingement angles at all acceleration pressures and particle sizes. Moreover, erosion rates of the samples were increased with increases in acceleration pressure at all particle impingement angles and particle sizes. On the other hand, erosion rates of the samples decrease with increase in erodent particle sizes. Hence, maximum erosion was observed when the aluminum alloy eroded at 15° impingement angle and 4 bar pressure by using 180 mesh erodent particles. Finally, the eroded surfaces of the samples were analyzed by using scanning electron microscope. The surfaces of the samples were also investigated by using energy dispersive X-ray analysis in scanning electron microscopy studies. Microcutting and microploughing erosion mechanisms were observed at 15° and 30° impingement angles, while deep cavities and valleys formed due to plastic deformation were observed at 45° and 60° impingement angles. Moreover, embedded erodent particles were clearly detected on the surfaces of the samples by energy dispersive X-ray analysis