Crack mechanical failure in lithium niobate crystal under ion irradiation; novel simulation by extended finite elements

Swift heavy ion irradiation (ions with mass heavier than 15 and energy exceeding MeV/amu) transfer their energy mainly to the electronic system with small momentum transfer per collision. Therefore, they produce linear regions (columnar nano-tracks) around the straight ion trajectory, with marked modifications with respect to the virgin material, e.g., phase transition, amorphization, compaction, changes in physical or chemical properties. In the case of crystalline materials the most distinctive feature of swift heavy ion irradiation is the production of amorphous tracks embedded in the crystal. Lithium niobate is a relevant optical material that presents birefringence due to its anysotropic trigonal structure. The amorphous phase is certainly isotropic. In addition, its refractive index exhibits high contrast with those of the crystalline phase. This allows one to fabricate waveguides by swift ion irradiation with important technological relevance. From the mechanical point of view, the inclusion of an amorphous nano-track (with a density 15% lower than that of the crystal) leads to the generation of important stress/strain fields around the track. Eventually these fields are the origin of crack formation with fatal consequences for the integrity of the samples and the viability of the method for nano-track formation. For certain crystal cuts (X and Y), these fields are clearly anisotropic due to the crystal anisotropy. We have used finite element methods to calculate the stress/strain fields that appear around the ion-generated amorphous nano-tracks for a variety of ion energies and doses. A very remarkable feature for X cut-samples is that the maximum shear stress appears on preferential planes that form +/-45º with respect to the crystallographic planes. This leads to the generation of oriented surface cracks when the dose increases. The growth of the cracks along the anisotropic crystal has been studied by means of novel extended finite element methods, which include cracks as discontinuities. In this way we can study how the length and depth of a crack evolves as function of the ion dose. In this work we will show how the simulations compare with experiments and their application in materials modification by ion irradiation.

Crack mechanical failure in ceramic materials under ion irradiation: case of lithium niobate crystal

Swift heavy ion irradiation (ions with mass heavier than 15 and energy exceeding MeV/amu) transfer their energy mainly to the electronic system with small momentum transfer per collision. Therefore, they produce linear regions (columnar nano-tracks) around the straight ion trajectory, with marked modifications with respect to the virgin material, e.g., phase transition, amorphization, compaction, changes in physical or chemical properties. In the case of crystalline materials the most distinctive feature of swift heavy ion irradiation is the production of amorphous tracks embedded in the crystal. Lithium niobate is a relevant optical material that presents birefringence due to its anysotropic trigonal structure. The amorphous phase is certainly isotropic. In addition, its refractive index exhibits high contrast with those of the crystalline phase. This allows one to fabricate waveguides by swift ion irradiation with important technological relevance. From the mechanical point of view, the inclusion of an amorphous nano-track (with a density 15% lower than that of the crystal) leads to the generation of important stress/strain fields around the track. Eventually these fields are the origin of crack formation with fatal consequences for the integrity of the samples and the viability of the method for nano-track formation. For certain crystal cuts (X and Y), these fields are clearly anisotropic due to the crystal anisotropy. We have used finite element methods to calculate the stress/strain fields that appear around the ion- generated amorphous nano-tracks for a variety of ion energies and doses. A very remarkable feature for X cut-samples is that the maximum shear stress appears on preferential planes that form +/-45º with respect to the crystallographic planes. This leads to the generation of oriented surface cracks when the dose increases. The growth of the cracks along the anisotropic crystal has been studied by means of novel extended finite element methods, which include cracks as discontinuities. In this way we can study how the length and depth of a crack evolves as function of the ion dose. In this work we will show how the simulations compare with experiments and their application in materials modification by ion irradiation.

Janet Guthrie quit after 79 laps because of mechanical failure

General note: Title and date provided by Bettye Lane.

Towards a fast electro-thermo-mechanical IGBT/Diode simulation framework for design of reliable power electronic converters

This paper describes a methodology that enables fast and reasonably accurate prediction of the reliability of power electronic modules featuring IGBTs and p-i-n diodes, by taking into account thermo-mechanical failure mechanisms of the devices and their associated packaging. In brief, the proposed simulation framework performs two main tasks which are tightly linked together: (i) the generation of the power devices' transient thermal response for realistic long load cycles and (ii) the prediction of the power modules' lifetime based on the obtained temperature profiles. In doing so the first task employs compact, physics-based device models, power losses lookup tables and polynomials and combined material-failure and thermal modelling, while the second task uses advanced reliability tests for failure mode and time-to-failure estimation. The proposed technique is intended to be utilised as a design/optimisation tool for reliable power electronic converters, since it allows easy and fast investigation of the effects that changes in circuit topology or devices' characteristics and packaging have on the reliability of the employed power electronic modules. © 2012 IEEE.

Extracting the Mechanical Properties of 1D Nanostructures from Nanoindentation

<正>The so-called one dimensional(1D) nanostructures or wirelike nanoentities,such as nanowire(NW),nanotube(NT),and nanobelt(NB) have attracted much interest in scientific community because of their remarkable mechanical,electrical,thermal properties and potential applications in wide variety of devices.The mechanical failure of 1D nanostructures can lead to the malfunction or even failure of entire device and 1D nanostructures may also have size-dependent properties. Therefore,an accurate measurement of their mechanical properties is of

Mechanistic-based Design-Integrated Reliability Validation Framework for Mechanical Systems

Abstract: New product design challenges, related to customer needs, product usage and environments, face companies when they expand their product offerings to new markets; Some of the main challenges are: the lack of quantifiable information, product experience and field data. Designing reliable products under such challenges requires flexible reliability assessment processes that can capture the variables and parameters affecting the product overall reliability and allow different design scenarios to be assessed. These challenges also suggest a mechanistic (Physics of Failure-PoF) reliability approach would be a suitable framework to be used for reliability assessment. Mechanistic Reliability recognizes the primary factors affecting design reliability. This research views the designed entity as a “system of components required to deliver specific operations”; it addresses the above mentioned challenges by; Firstly: developing a design synthesis that allows a descriptive operations/ system components relationships to be realized; Secondly: developing component’s mathematical damage models that evaluate components Time to Failure (TTF) distributions given: 1) the descriptive design model, 2) customer usage knowledge and 3) design material properties; Lastly: developing a procedure that integrates components’ damage models to assess the mechanical system’s reliability over time. Analytical and numerical simulation models were developed to capture the relationships between operations and components, the mathematical damage models and the assessment of system’s reliability. The process was able to affect the design form during the conceptual design phase by providing stress goals to meet component’s reliability target. The process was able to numerically assess the reliability of a system based on component’s mechanistic TTF distributions, besides affecting the design of the component during the design embodiment phase. The process was used to assess the reliability of an internal combustion engine manifold during design phase; results were compared to reliability field data and found to produce conservative reliability results. The research focused on mechanical systems, affected by independent mechanical failure mechanisms that are influenced by the design process. Assembly and manufacturing stresses and defects’ influences are not a focus of this research.

Mechanical circulatory support for destination therapy.

Patients with chronic heart failure who are not eligible for heart transplant and whose life expectancy depends mainly on the heart disease may benefit from mechanical circulatory support. Mechanical circulatory support restores adequate cardiac output and organ perfusion and eventually improves patients' clinical condition, quality of life and life expectancy. This treatment is called destination therapy (DT) and we estimate that in Switzerland more than 120 patients per year could benefit from it. In the last 10 years, design of the devices, implantation techniques and prognoses have changed dramatically. The key to successful therapy with a left ventricular assist device is appropriate patient selection, although we are still working on the definition of reliable inclusion and exclusion criteria and optimal timing for surgical implantation. Devices providing best long-term results are continuous flow, rotary or axial blood pumps implanted using minimally invasive techniques on a beating heart. These new devices (Thoratec HeartMate II and HeartWare HVAD) have only a single moving part, and have improved durability with virtually 10 years freedom from mechanical failure. In selected patients, the overall actuarial survival of DT patients is 75% at 1 year and 62% at 2 years, with a clear improvement in quality of life compared with medical management only. Complications include bleeding and infections; their overall incidence is significantly lower than with previous devices and their management is well defined. DT is evolving into an effective and reasonably cost-effective treatment option for a growing population of patients not eligible for heart transplant, showing encouraging survival rates at 2 years and providing clear improvement in quality of life. The future is bright for people suffering from chronic heart failure.

Obesity, age, sex, diagnosis, and fixation mode differently affect early cup failure in total hip arthroplasty: a matched case-control study of 4420 patients

Studies about the influence of patient characteristics on mechanical failure of cups in total hip replacement have applied different methodologies and revealed inconclusive results. The fixation mode has rarely been investigated. Therefore, we conducted a detailed analysis of the influence of patient characteristics and fixation mode on cup failure risks.

Assessment of biodegradable magnesium alloys for enhanced mechanical and biocompatible properties

Biomaterials have been used for more than a century in the human body to improve body functions and replace damaged tissues. Currently approved and commonly used metallic biomaterials such as, stainless steel, titanium, cobalt chromium and other alloys have been found to have adverse effects leading in some cases, to mechanical failure and rejection of the implant. The physical or chemical nature of the degradation products of some implants initiates an adverse foreign body reaction in the tissue. Some metallic implants remain as permanent fixtures, whereas others such as plates, screws and pins used to secure serious fractures are removed by a second surgical procedure after the tissue has healed sufficiently. However, repeat surgical procedures increase the cost of health care and the possibility of patient morbidity. This study focuses on the development of magnesium based biodegradable alloys/metal matrix composites (MMCs) for orthopedic and cardiovascular applications. The Mg alloys/MMCs possessed good mechanical properties and biocompatible properties. Nine different compositions of Mg alloys/MMCs were manufactured and surface treated. Their degradation behavior, ion leaching, wettability, morphology, cytotoxicity and mechanical properties were determined. Alloying with Zn, Ca, HA and Gd and surface treatment resulted in improved mechanical properties, corrosion resistance, reduced cytotoxicity, lower pH and hydrogen evolution. Anodization resulted in the formation of a distinct oxide layer (thickness 5-10 μm) as compared with that produced on mechanically polished samples (~20-50 nm) under ambient conditions. It is envisaged that the findings of this research will introduce a new class of Mg based biodegradable alloys/MMCs and the emergence of innovative cardiovascular and orthopedic implant devices.^

Magnitude and variability of loading on the osseointegrated implant of transfemoral amputees during walking

This study directly measured the load acting on the abutment of the osseointegrated implant system of transfemoral amputees during level walking, and studied the variability of the load within and among amputees. Twelve active transfemoral amputees (age: 54±12 years, mass:84.3±16.3 kg, height: 17.8±0.10 m) fitted with an osseointegrated implant for over 1 year participated in the study. The load applied on the abutment was measured during unimpeded, level walking in a straight line using a commercial six-channel transducer mounted between the abutment and the prosthetic knee. The pattern and the magnitude of the three-dimensional forces and moments were revealed. Results showed a low step-to-step variability of each subject, but a high subject-to-subject variability in local extrema of body-weight normalized forces and moments and impulse data. The high subject-to-subject variability suggests that the mechanical design of the implant system should be customized for each individual, or that a fit-all design should take into consideration the highest values of load within a broad range of amputees. It also suggests specific loading regime in rehabilitation training are necessary for a given subject. Thus the loading magnitude and variability demonstrated should be useful in designing an osseointegrated implant system better able to resist mechanical failure and in refining the rehabilitation protocol.

Curvedness study on atherosclerosis plaques and its implications to plaque stress

Atherosclerosis plaque rupture has been considered to be a mechanical failure of the thin fibrous cap, resulted from extreme plaque stress. Plaque stress was affected by many factors from morphological features to biological abnormalities. In this study, geometrical factors (curvedness, fibrous cap thickness) were studied on assessing plaque vulnerability in comparison with stress analysis results obtained by fluid structure interaction from 20 human carotid atherosclerosis plaques. The results show that plaque surface curvedness could contribute to extreme stress level, especially in plaque shoulder region. General plaque stress distribution could be predicted by fibrous cap thickness and curvedness with multi-regression model. With more features included in the regression model, plaque stress could be easily calculated and used to assess plaque vulnerability.

Carbon-based silicon nanohybrid anode materials for rechargeable lithium ion batteries

Silicon has demonstrated great potential as anode materials for next-generation high-energy density rechargeable lithium ion batteries. However, its poor mechanical integrity needs to be improved to achieve the required cycling stability. Nano-structured silicon has been used to prevent the mechanical failure caused by large volume expansion of silicon. Unfortunately, pristine silicon nanostructures still suffer from quick capacity decay due to several reasons, such as formation of solid electrolyte interphase, poor electrical contact and agglomeration of nanostructures. Recently, increasing attention has been paid to exploring the possibilities of hybridization with carbonaceous nanostructures to solve these problems. In this review, the recent advances in the design of carbon-silicon nanohybrid anodes and existing challenges for the development of high-performance lithium battery anodes are briefly discussed.

Potential and electric field distribution in a ceramic disc insulator string with faulty insulators

Ceramic/Porcelain suspension disc insulators are widely used in power systems to provide electrical insulation and mechanically support for high-voltage transmission lines. These insulators are subjected to a variety of stresses, including mechanical, electrical and environmental. These stresses act in unison. The exact nature and magnitude of these stresses vary significantly and depends on insulator design, application and its location. Due to various reasons the insulator disc can lose its electrical insulation properties without any noticeable mechanical failure. Such a condition while difficult to recognize, can enhance the stress on remaining healthy insulator discs in the string further may lead to a flashover. To understand the stress enhancement due to faulty discs in a string, attempt has been made to simulate the potential and electric field profiles for various disc insulators presently used in the country. The results of potential and electric filed stress obtained for normal and strings with faulty insulator discs are presented.