Development of FEA models to study contusion patterning in layered tissue and the shaft loaded blister test

In the natural world there is no such thing as a perfectly sharp edge, either thru wear or machining imprecation at the macroscopic scale all edges have curvature. This curvature can have significant impact when comparing results with theory. Both numerical and analytic models for the contact of an object with a sharp edge predict infinite stresses which are not present in the physical world. It is for this reason that the influence of rounded edges must be studied to better understand how they affect model response. Using a commercial available finite element package this influence will be studied in two different problems; how this edge geometry effects the shape of a contusion (bruise) and the accuracy of analytic models for the shaft loaded blister test (SLBT). The contusion study presents work that can be used to enable medical examiners to better determine if the object in question was capable of causing the contusions present. Using a simple layered tissue model which represents a generic location on the human body, a sweep of objects with different edges properties is studied using a simple strain based injury metric. This analysis aims to examine the role that contact area and energy have on the formation, location, and shape of the resulting contusion. In studying the SLBT with finite element analysis and cohesive zone modeling, the assessment of various analytic models will provide insight into how to accurately measure the fracture energy for both the simulation and experiment. This provides insight into the interactions between a film, the substrate it is bonded to and the loading plug. In addition, parametric studies are used to examine potential experimental designs and enable future work in this field. The final product of this project provides tools and insight into future study of the effect rounded edges have on contact and this work enables for more focused studies within desired regimes of interest

The application of fracture mechanics to Mode I interfacial ice delamination and plasticity induced crack closure

The work presented in this dissertation focuses on the application of fracture mechanics principles and experimental techniques on two different engineering problems. The first portion of this dissertation is on applying interfacial fracture mechanics and plate theory to develop a plate deformation model, which determines the initiation and steady-state interfacial fracture toughness for a crack under mode I loading. The second application details plasticity-induced crack closure for surface fatigue cracks under mode I loading using surface displacement analysis to calculate the residual stress distribution and crack opening levels. For engineering structures that operate in cold weather climates and aircraft in flight, ice accretion presents a significant hazard to continued safe operation. To improve the performance of de-icing systems designed to remove ice post-formation, an understanding of the mechanics of ice delamination can drastically improve de-icing performance. To study interfacial ice delamination the most common types of tests are collectively known as strength-based adhesion tests, which measure the maximum stresses the interface can support before failure. While these tests can provide information about the ultimate strength of the interface, it is not possible to conduct experiments with stable interfacial delamination, and the results reported span an entire order of magnitude for similar surface finishes. To conduct a fracture mechanics-based experiment where stable interfacial delamination occurs, shaft-loaded blister test is proposed as a configuration capable of studying the effect of ice layer thickness and substrate surface roughness. Results show the initiation fracture toughness is independent of both factors for the range of values studied. To study the effect growing delamination size has on the fracture toughness; a novel model for the ice layer displacement is developed, enabling the prediction of the crack length based on macroscopic force and displacement measurements. A continuous boundary condition capable of modeling any plate compliance between perfectly fixed and simply support is applied to allow for modeling plates over a wide range of ice layer thicknesses. The application of fracture mechanics to plasticity-induced crack closure extends current measurement techniques to include measurement of the closure point (false crack tip), depth opening, and the closure stress distribution. For cracks grown via fatigue, crack closure mechanisms enable the partial transfer of the stresses generated during a loading cycle between the crack flanks instead of developing a stress concentration at the crack tip. To determine the crack opening state, surface displacement analysis was conducted using digital image correlation to measure the crack opening displacement along the length of the crack. By fitting an incremental crack-opening model to the surface displacement measurements for a range of applied loads, two different properties can be calculated: the residual stress distribution along the crack length and the crack opening into the depth of the sample. The residual closure stress distribution is calculated by partially opening the crack and calculating the change in normal traction required to cause such a change in crack length. The crack depth opening is recovered by measuring the surface compliance of the sample for a given applied load increment. Both measurements are verified using finite element simulations, and a range of crack lengths are studied in both cases

The application of fracture mechanics to Mode I interfacial ice delamination and plasticity induced crack closure

The work presented in this dissertation focuses on the application of fracture mechanics principles and experimental techniques on two different engineering problems. The first portion of this dissertation is on applying interfacial fracture mechanics and plate theory to develop a plate deformation model, which determines the initiation and steady-state interfacial fracture toughness for a crack under mode I loading. The second application details plasticity-induced crack closure for surface fatigue cracks under mode I loading using surface displacement analysis to calculate the residual stress distribution and crack opening levels. For engineering structures that operate in cold weather climates and aircraft in flight, ice accretion presents a significant hazard to continued safe operation. To improve the performance of de-icing systems designed to remove ice post-formation, an understanding of the mechanics of ice delamination can drastically improve de-icing performance. To study interfacial ice delamination the most common types of tests are collectively known as strength-based adhesion tests, which measure the maximum stresses the interface can support before failure. While these tests can provide information about the ultimate strength of the interface, it is not possible to conduct experiments with stable interfacial delamination, and the results reported span an entire order of magnitude for similar surface finishes. To conduct a fracture mechanics-based experiment where stable interfacial delamination occurs, shaft-loaded blister test is proposed as a configuration capable of studying the effect of ice layer thickness and substrate surface roughness. Results show the initiation fracture toughness is independent of both factors for the range of values studied. To study the effect growing delamination size has on the fracture toughness; a novel model for the ice layer displacement is developed, enabling the prediction of the crack length based on macroscopic force and displacement measurements. A continuous boundary condition capable of modeling any plate compliance between perfectly fixed and simply support is applied to allow for modeling plates over a wide range of ice layer thicknesses. The application of fracture mechanics to plasticity-induced crack closure extends current measurement techniques to include measurement of the closure point (false crack tip), depth opening, and the closure stress distribution. For cracks grown via fatigue, crack closure mechanisms enable the partial transfer of the stresses generated during a loading cycle between the crack flanks instead of developing a stress concentration at the crack tip. To determine the crack opening state, surface displacement analysis was conducted using digital image correlation to measure the crack opening displacement along the length of the crack. By fitting an incremental crack-opening model to the surface displacement measurements for a range of applied loads, two different properties can be calculated: the residual stress distribution along the crack length and the crack opening into the depth of the sample. The residual closure stress distribution is calculated by partially opening the crack and calculating the change in normal traction required to cause such a change in crack length. The crack depth opening is recovered by measuring the surface compliance of the sample for a given applied load increment. Both measurements are verified using finite element simulations, and a range of crack lengths are studied in both cases

Brazilian Flora 2020: Leveraging the power of a collaborative scientific network

International audienceThe shortage of reliable primary taxonomic data limits the description of biological taxa and the understanding of biodiversity patterns and processes, complicating biogeographical, ecological, and evolutionary studies. This deficit creates a significant taxonomic impediment to biodiversity research and conservation planning. The taxonomic impediment and the biodiversity crisis are widely recognized, highlighting the urgent need for reliable taxonomic data. Over the past decade, numerous countries worldwide have devoted considerable effort to Target 1 of the Global Strategy for Plant Conservation (GSPC), which called for the preparation of a working list of all known plant species by 2010 and an online world Flora by 2020. Brazil is a megadiverse country, home to more of the world's known plant species than any other country. Despite that, Flora Brasiliensis, concluded in 1906, was the last comprehensive treatment of the Brazilian flora. The lack of accurate estimates of the number of species of algae, fungi, and plants occurring in Brazil contributes to the prevailing taxonomic impediment and delays progress towards the GSPC targets. Over the past 12 years, a legion of taxonomists motivated to meet Target 1 of the GSPC, worked together to gather and integrate knowledge on the algal, plant, and fungal diversity of Brazil. Overall, a team of about 980 taxonomists joined efforts in a highly collaborative project that used cybertaxonomy to prepare an updated Flora of Brazil, showing the power of scientific collaboration to reach ambitious goals. This paper presents an overview of the Brazilian Flora 2020 and provides taxonomic and spatial updates on the algae, fungi, and plants found in one of the world's most biodiverse countries. We further identify collection gaps and summarize future goals that extend beyond 2020. Our results show that Brazil is home to 46,975 native species of algae, fungi, and plants, of which 19,669 are endemic to the country. The data compiled to date suggests that the Atlantic Rainforest might be the most diverse Brazilian domain for all plant groups except gymnosperms, which are most diverse in the Amazon. However, scientific knowledge of Brazilian diversity is still unequally distributed, with the Atlantic Rainforest and the Cerrado being the most intensively sampled and studied biomes in the country. In times of “scientific reductionism”, with botanical and mycological sciences suffering pervasive depreciation in recent decades, the first online Flora of Brazil 2020 significantly enhanced the quality and quantity of taxonomic data available for algae, fungi, and plants from Brazil. This project also made all the information freely available online, providing a firm foundation for future research and for the management, conservation, and sustainable use of the Brazilian funga and flora