Mechanistic Understanding of High Strain Rate Impact Behavior of Ultra-high Molecular Weight Polyethylene and the Mechanism of Coating Formation During Cold Spraying PDF Download
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Author: Kesavan Ravi
Publisher:
ISBN:
Category :
Languages : en
Pages : 198
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Book Description
Recent developments showed polymer coatings to be feasible by cold spray (CS) technique on different surfaces. This is especially important for Ultra-High Molecular Weight Polyethylene (UHMWPE) which cannot be classically processed. But the mechanisms behind coating formation was not largely understood. The thesis presents a mechanistic understanding of high strain rate impact behavior of Ultra-High Molecular Weight Polyethylene and the mechanism of coating formation during CS. The coating formation is first broken down into two major categories: 1. Interaction of UHMWPE with Al substrate (impacting particle-substrate interaction) during a high-speed impact and interaction of UHMWPE with already deposited UHMWPE particles (impacting particle-deposited particles) leading to a buildup in the coating. First stage of coating formation was understood from a technique developed for this work called Isolated Particle Deposition (IPD). In the experimental IPD process, effects of gas temperature and FNA content were calibrated empirically by depositing UHMWPE particles in an isolated manner on an Al substrate. The Deposition efficiency increased with gas temperature and FNA content. The use of an ultrafast video-camera helped to determine the particle velocity, and theoretical calculations helped to evaluate the temperature of UHMWPE particles before and during the impact process. Mechanical response of UHMWPE at different temperatures were understood by calculating elastic strain energy of UHMWPE which decreased with increasing material temperature and increased with the strain rate. Rebound of UHMWPE particles on Al surface depended upon whether UHMWPE particles after impact furnished a contact area with an interfacial bond stronger than elastic strain energy of the particle. External contributions like H-bonds on the FNA surface provide sufficiently strong extra bonds at the contact surface to increase the window of deposition at higher temperatures, which was otherwise very low. Second stage of coating formation was understood from the mechanism of welding of UHMWPE grains at different interfacial loading conditions and at varying FNA contents. The morphological and mechanical characterization showed that when UHMWPE was processed under high loading conditions (using classical sintering technique), FNA particles reinforced the UHMWPE interface. On the contrary, when UHMWPE was processed under low loading conditions, FNA particles weakened the interface. Last to be discussed in the thesis is the strain rate effect of UHMWPE using Split-Hopkinson Pressure Bar (SHPB) experiments, in order to approach comparable conditions to what happens during particle impacts. This part of the study discussed in detail the effects a high strain-rate compression has on UHMWPE by analyzing its stress-strain curves, with and without FNA. Thus, the mechanical response data with the inclusion 0%, 4% and 10% FNA to UHMWPE is also presented and discussed.
Author: Kesavan Ravi
Publisher:
ISBN:
Category :
Languages : en
Pages : 198
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Book Description
Recent developments showed polymer coatings to be feasible by cold spray (CS) technique on different surfaces. This is especially important for Ultra-High Molecular Weight Polyethylene (UHMWPE) which cannot be classically processed. But the mechanisms behind coating formation was not largely understood. The thesis presents a mechanistic understanding of high strain rate impact behavior of Ultra-High Molecular Weight Polyethylene and the mechanism of coating formation during CS. The coating formation is first broken down into two major categories: 1. Interaction of UHMWPE with Al substrate (impacting particle-substrate interaction) during a high-speed impact and interaction of UHMWPE with already deposited UHMWPE particles (impacting particle-deposited particles) leading to a buildup in the coating. First stage of coating formation was understood from a technique developed for this work called Isolated Particle Deposition (IPD). In the experimental IPD process, effects of gas temperature and FNA content were calibrated empirically by depositing UHMWPE particles in an isolated manner on an Al substrate. The Deposition efficiency increased with gas temperature and FNA content. The use of an ultrafast video-camera helped to determine the particle velocity, and theoretical calculations helped to evaluate the temperature of UHMWPE particles before and during the impact process. Mechanical response of UHMWPE at different temperatures were understood by calculating elastic strain energy of UHMWPE which decreased with increasing material temperature and increased with the strain rate. Rebound of UHMWPE particles on Al surface depended upon whether UHMWPE particles after impact furnished a contact area with an interfacial bond stronger than elastic strain energy of the particle. External contributions like H-bonds on the FNA surface provide sufficiently strong extra bonds at the contact surface to increase the window of deposition at higher temperatures, which was otherwise very low. Second stage of coating formation was understood from the mechanism of welding of UHMWPE grains at different interfacial loading conditions and at varying FNA contents. The morphological and mechanical characterization showed that when UHMWPE was processed under high loading conditions (using classical sintering technique), FNA particles reinforced the UHMWPE interface. On the contrary, when UHMWPE was processed under low loading conditions, FNA particles weakened the interface. Last to be discussed in the thesis is the strain rate effect of UHMWPE using Split-Hopkinson Pressure Bar (SHPB) experiments, in order to approach comparable conditions to what happens during particle impacts. This part of the study discussed in detail the effects a high strain-rate compression has on UHMWPE by analyzing its stress-strain curves, with and without FNA. Thus, the mechanical response data with the inclusion 0%, 4% and 10% FNA to UHMWPE is also presented and discussed.
Author:
Publisher:
ISBN:
Category : Mechanics, Applied
Languages : en
Pages : 348
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Book Description
Author: Ray A. Gsell
Publisher: ASTM International
ISBN: 0803124821
Category : Creep
Languages : en
Pages : 139
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Book Description
Proceedings of a November 1996 symposium held in New Orleans, Louisiana, providing a forum for presentations and discussions of issues critical to the understanding of ultra-high molecular weight polyethylene (UHMWPE) as used in medical and surgical devices. Eleven papers are grouped in three sectio
Author: Claire E. Griesbach
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
Understanding the process-structure-property relations is imperative when designing materials for critical applications, especially when exposed to extreme environments. Clever design of materials containing structural heterogeneities or features spanning multiple length scales can provide synergistically improved properties well beyond the limits of their homogeneous components or provide predictable and acceptable failure modes. In this work, we investigate the process-structure-property relations and the potential for improved performance of materials exposed to the extreme environments of high-velocity impact and irradiation.Similar to material processing techniques such as shot peening and cold spray which induce structural changes through high-velocity impact, we perform well-controlled single microprojectile impact tests of silver (Ag) single crystals which allows for clear correlation of the post-deformation microstructures to the impact-induced plasticity mechanisms. When comparing the impacted microsamples to their pristine single crystal counterparts, we find that the high-strain rates achieved during impact ([epsilon]~108 s-1) induce dramatic structural changes including extensive grain refinement, dislocation density gradients, and a martensitic phase transformation, while the quasi-statically ([epsilon]=10-2 s-1) compressed Ag microcubes remain single crystalline. The impacted samples show a synergistic improvement in strength and toughness, each on average over twice the respective properties of single crystal and bulk polycrystal Ag samples. Such synergistic improvements result from heterogeneous deformation induced stress and strain gradients. Progressive yielding of the gradient grain structure causes enhanced nucleation and pile-up of dislocations in the relatively softer domains to accommodate the elastic-plastic mismatch between grains. The observed dislocation accumulation-which is higher in larger grains-provides ultra-high strain hardening. Additionally, enhanced toughness is achieved through intergranular plasticity mechanisms such as nanograin rotation and grain boundary migration, leading to grain coalescence. These complementary inter- and intragranular plasticity mechanisms elicit improved mechanical properties. We demonstrate the ability to tune the dominant plasticity mechanisms-and thus the resultant properties-through control over the crystal orientation and impact velocity. Our findings provide new understandings of impact-induced nanostructural evolution and mechanistic pathways to improve mechanical properties through heterogeneous deformation, which can be used to improve high strain rate metal processing techniques. The second research thrust examines the effects of structural heterogeneity on the mechanical properties, performance, and failure of tristructural isotropic (TRISO) coated nuclear fuel particles. We examine the irradiation-induced densification and fracture behavior of the porous pyrocarbon buffer layer, which has pronounced effects on the overall particle's performance. Microstructural characterization of the initial as-fabricated buffer layer reveals a gradient of increasing porosity in the radial direction with the porosity reaching a maximum near the buffer-IPyC interface-which is commonly where circumferential tearing initiates in the buffer layer. Using the as-fabricated buffer structure as a basis to investigate the irradiation-induced structural changes, we study the influences of irradiation temperature and fluence on buffer layer response, by characterizing multiple TRISO particles from three different irradiation condition groups. The high temperatures, radiation damage, and mechanical stresses applied to the buffer layer during irradiation cause irradiation condition-dependent micro and nanostructural changes: localized densification near the kernel occurs in particles exposed to relatively lower temperatures, whereas significant changes in the entire pore microstructure occur in particles irradiated under high temperature and fluence. Intriguingly, a large proportion of the total buffer layer densification is accommodated through graphitization of the pyrocarbon rather than the changes in the pore microstructure. Significant nanostructural changes-including an increase in crystallite size, decrease in interplanar spacing, and formation of onion-like graphitic structures-contribute to densification and are most pronounced in the samples exposed to the highest temperature and fluence. Our findings provide a new detailed understanding of the irradiation-induced densification and fracture behavior of the pyrocarbon buffer layer in TRISO nuclear fuel particles, which will enable better predictions of buffer failure, aid in improved future designs, and provide guidance on the acceptable usage of these particles given different reactor conditions.
Author:
Publisher:
ISBN:
Category : Composite materials
Languages : en
Pages : 790
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Book Description
Author: Galip Yilmaz
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
In this work, the processing of a unique ultra-high molecular weight polyethylene (UHMWPE) polymer, in both powder and pellet form, using both regular and special injection molding techniques, was investigated in an effort to mass produce this high-grade specialty polymer. The goals of this study were to (i) improve the processability of UHMWPE, (ii) enhance the mechanical performance and overall quality of the molded parts, and (iii) develop an in-depth understanding of how the supercritical fluid (SCF), machine configuration, mold compression, mold insulating techniques, and process conditions affect the flow behavior and final quality of the injection molded UHMWPE. In the first study, two common atmospheric gases in their supercritical states-namely, nitrogen (scN2) and carbon dioxide (scCO2)-were used as processing aids in a special full-shot, high-pressure microcellular injection molding (MIM) process for processing UHMWPE pellets. The mechanical properties in terms of tensile strength, Young's modulus, and elongation-at break of the SCF-loaded samples were examined. The thermal and rheological properties of regular and SCF-loaded samples were also analyzed using differential scanning calorimetry (DSC) and parallel-plate rheometry, respectively. It was found that the processing of UHMWPE with both gases effectively reduced the thermal degradation of the material and the injection pressure, compared to regular injection molding, while still retaining the mechanical properties of the resin. In the second part, a follow-up study was conducted on conventional injection molding (IM), along with the special full-shot, high-pressure microcellular injection molding (MIM) using UHMWPE in pellet form. A relatively complicated and thin-walled mold design was used to produce box-shaped parts with varying wall thickness. Although different processing settings were tested in order to eliminate persistent short shot issues, only high-pressure MIM processing was able to fill parts completely. Furthermore, not only did high-pressure MIM processing effectively promote the processability of UHMWPE, it also reduced the very high injection pressure requirement and the high part shrinkage issues associated with the IM samples. In the third study, UHMWPE powder was processed using injection molding (IM) and injection-compression molding (ICM). The processing parameters of feeding the powders were optimized to ensure proper dosage and to avoid damaging UHMWPE's molecular structure. Dynamic mechanical analysis (DMA) and Fourier-transform infrared spectroscopy (FTIR) tests confirmed that the thermal and oxidative degradation of the material was minimized but crosslinking was induced during molding. Tensile tests and impact tests showed that the ICM samples were superior to the IM samples. A delamination skin layer was formed on the IM sample surfaces, while it was absent in the ICM samples, thus suggesting two different flow behaviors between IM and ICM during the packing phase. The delamination layer defect was the subject of the fourth study as one of the main challenges of UHMWPE molding. The delamination layer hampers UHMWPE's two key properties: wear resistance and impact strength. A mold insulation method was employed to eliminate the formation of the delamination layer. The working principle of the method was to reduce the cooling rate and the shear stress of the polymer while improving polymer chain "interdiffusion" across the entangled chain bundles during the injection filling stage via a low thermal conductivity mold coating (e.g., epoxy coating). This method yielded molded parts free of delamination by delaying skin cooling during filling and packing. Therefore, it produced parts with enhanced mechanical properties, excellent impact strength, and improved surface quality.
Author: Thomas Hannah
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
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Book Description
The goal of this work is twofold. One part is to develop both the experimental techniques and advanced finite element modeling techniques necessary for understanding and analyzing data collected using a miniature 3.16 mm diameter Kolsky bar or Split Hopkinson Pressure Bar for high rate experimentation. Additionally, a robust analysis technique to gather statistically significant data is developed to simplify the experimental data gathering process and ensure the significance of the results. The work focuses mainly of the development of the Kolsky equipment and techniques, as well as methods for identifying error sources during testing. Additionally, models of the SHPB system have been generated using the finite element code Abaqus®, and are used throughout the project to aid in system characterization and experimental design efforts. Special attention is paid to the differences between miniature systems and full size ones, especially where data collection rates and sampling frequency are concerned. The use and characterization of paper pulse shapers is also developed to aid in the testing of UHMWPE samples at rates in excess of 10^4 strain per second. The second aspect of this work is to apply these techniques to the characterization of Dyneema® which is a composite consisting of Ultra High Molecular Weight Polyethylene (UHMWPE) fibers set in a polymer matrix, in this case HB26 hard laminate. Additionally, this work entails the design and implementation of full scale high speed impact tests using UHMWPE targets in multiple configurations to examine the variation in response due to a change in initial conditions and to evaluate the change in damage mechanisms. Finally, high resolution Computer Tomography or CT scans are used to evaluate the damage mechanisms observed in both the Kolsky bar testing and the plate impact testing nondestructively and without otherwise effecting the failure surfaces and structures. Mechanisms displayed in the Kolsky experiments are then compared to those observed in the plate impact tests to determine if and where the type of data collected from Kolsky bar tests can be applied to any future modeling efforts of the composite. Three fundamental knowledge gaps to be addressed in this work are: 1) Can a newer generation of "miniature" Kolsky bars generate repeatable and reproducible data? 2) How does Dyneema® respond differently increasing the strain rate from 10^3 strain per second to 10^4 strain per second? 3) Are there similar damage mechanisms seen in small scale Kolsky tests and large scale impact tests, and where could the Kolsky bar data be applied to future modeling efforts?
Author: Pasquale Cavaliere
Publisher: Springer
ISBN: 3319671839
Category : Technology & Engineering
Languages : en
Pages : 570
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Book Description
This book combines the contributions of experts in the field to describe the behavior of various materials, micromechanisms involved during processing, and the optimization of cold-spray technology. It spans production, characterization, and applications including wear resistance, fatigue, life improvement, thermal barriers, crack repair, and biological applications. Cold spray is an innovative coating technology based on the kinetic energy gained by particles sprayed at very high pressures. While the technique was developed in the 1990s, industrial and scientific interest in this technology has grown vastly in the last ten years. Recently, many interesting applications have been associated with cold-sprayed coatings, including wear resistance, fatigue life improvement, thermal barriers, biological applications, and crack repair. However, many fundamental aspects require clarification and description.
Author: Steven M. Kurtz
Publisher: Academic Press
ISBN: 9780080884448
Category : Technology & Engineering
Languages : en
Pages : 568
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Book Description
UHMWPE Biomaterials Handbook describes the science, development, properties and application of of ultra-high molecular weight polyethylene (UHMWPE) used in artificial joints. This material is currently used in 1.4 million patients around the world every year for use in the hip, knee, upper extremities, and spine. Since the publication of the 1st edition there have been major advances in the development and clinical adoption of highly crosslinked UHMWPE for hip and knee replacement. There has also been a major international effort to introduce Vitamin E stabilized UHMWPE for patients. The accumulated knowledge on these two classes of materials are a key feature of the 2nd edition, along with an additional 19 additional chapters providing coverage of the key engineering aspects (biomechanical and materials science) and clinical/biological performance of UHMWPE, providing a more complete reference for industrial and academic materials specialists, and for surgeons and clinicians who require an understanding of the biomaterials properties of UHMWPE to work successfully on patient applications. The UHMWPE Handbook is the comprehensive reference for professionals, researchers, and clinicians working with biomaterials technologies for joint replacement New to this edition: 19 new chapters keep readers up to date with this fast moving topic, including a new section on UHMWPE biomaterials; highly crosslinked UHMWPE for hip and knee replacement; Vitamin E stabilized UHMWPE for patients; clinical performance, tribology an biologic interaction of UHMWPE State-of-the-art coverage of UHMWPE technology, orthopedic applications, biomaterial characterisation and engineering aspects from recognised leaders in the field
Author: Anatolii Papyrin
Publisher: Elsevier
ISBN: 9780080465487
Category : Science
Languages : en
Pages : 336
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Book Description
The topic of this book is Cold Spray technology. Cold Spray is a process of applying coatings by exposing a metallic or dielectric substrate to a high velocity (300 to 1200 m/s) jet of small (1 to 50 μm) particles accelerated by a supersonic jet of compressed gas. This process is based on the selection of the combination of particle temperature, velocity, and size that allows spraying at the lowest temperature possible. In the Cold Spray process, powder particles are accelerated by the supersonic gas jet at a temperature that is always lower than the melting point of the material, resulting in coating formation from particles in the solid state. As a consequence, the deleterious effects of high-temperature oxidation, evaporation, melting, crystallization, residual stresses, gas release, and other common problems for traditional thermal spray methods are minimized or eliminated. This book is the first of its kind on the Cold Spray process. Cold Spray Technology covers a wide spectrum of various aspects of the Cold Spray technology, including gas-dynamics, physics of interaction of high-speed solid particles with a substrate as well as equipment, technologies, and applications. Cold Spray Technology includes the results of more than 20 years of original studies (1984-2005) conducted at the Institute of Theoretical and Applied Mechanics of the Siberian Division of the Russian Academy of Science, as well as the results of studies conducted at most of the research centres around the world. The authors' goal is threefold. The first goal is to explain basic principles and advantages of the Cold Spray process. The second goal is, to give practical information on technologies and equipment. The third goal is to present the current state of research and development in this field over the world. The book provides coverage and data that will be of interest for users of Cold Spray technology as well as for other coating experts. At the present time the Cold Spray method is recognized by world leading scientists and specialists. A wide spectrum of research is being conducted at many research centres and companies in many countries. New approach to spray coatings Results are exceptionally pure coatings Low spray temperature without degradation of powder and substrate materials High productivity, high deposition efficiency High operational safety because of absence of high temperature gas jets, radiation and explosive gases Excellent thermal and electrical conductivity Wide spectrum of applications because of important advantages of the process
