Evolving Material Porosity on an Additive Manufacturing Simulation with the Generalized Method of Cells

The effect of material porosity on final part distortion and residual stresses in a selective laser sintering manufacturing simulation is presented here. A time-dependent thermomechanical model is used with the open-source FEA software CalculiX. Effective homogenized material properties for Inconel 625 are precomputed using NASAs Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC). The evolving porosity of the material is estimated with each pass of the laser beam during simulation runtime. A comparison with a homogenous model and the evolving model shows that the evolving porous model predicts larger distortions with greater residual stresses

T650/AFR-PE-4/FM680-1 Mode I Critical Energy Release Rate at High Temperatures: Experiments and Numerical Models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76240/1/AIAA-2007-2305-492.pd

Efficient and Robust Traction Laws for the Modeling of Adhesively Bonded Joints

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76317/1/AIAA-2008-1847-586.pd

Predictions of Delamination of a Stiffened Panel Using a Cohesive Zone Model

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/83573/1/AIAA-2010-2617-230.pd

Analytical and Experimental Methods for Adhesively Bonded Joints Subjected to High Temperatures.

Recent advances in material systems have expanded the temperature range over which adhesively bonded composite joints can be used. In this work, several tools are developed for use in modeling joints over a broad range of temperatures. First, a set of dimensionless parameters is established which can be used for analysis of joint performance for an orthotropic symmetric double lap joint. A critical dimensionless ratio of mechanical and thermal loads is identified. The ratio predicts characteristics of the resulting stress distribution. A bonded joint finite element is also developed, wherein a joint-specific finite element is formulated based on an analytical solution. The resulting element allows for mesh-independent joint evaluation and multi-joint simulation at a system or vehicle level. As a mid-level analysis technique, the element has significant predictive and cost advantages over the previously available methods. An advanced analysis technique, the discrete cohesive zone method, is developed and demonstrated in a general element formulation. Initially, the element is examined from the perspective of computational efficiency and robustness. Two efficient traction laws are formulated and are compared to a traction law that is in common use. The element is subsequently used to investigate the interactions of adhesive parameters in standard adhesive characterization experiments. This quantification of experimental sensitivities allows for a deliberate mapping of cumulative experimental results to an appropriate set of model constitutive parameters. With knowledge of the parameter interactions, a set of experimental results are interpreted to determine a set of adhesive constitutive parameters for T650/AFR-PE-4/FM680-1, a high temperature material system of current interest.Ph.D.Aerospace EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/60791/1/petegus_1.pd

Dimensionless parameters in symmetric double lap joints: an orthotropic solution for thermomechanical loading

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76627/1/AIAA-2006-1959-520.pd

Integration of MAC/GMC into CalculiX, an Open Source Finite Element Code

An analysis framework is presented that makes available multiscale analysis of composite structures using the open-source FEA solver package CalculiX CrunchiX (CCX). At the center of this framework is the coupling of the Finite Element Analysis - Micromechanics Analysis Code (FEAMAC) library from NASA's Micromechanics Analysis Code with Generalized Method of Cells (MAC/GMC) to allow micromechanics analysis. The results show that the proposed coupling can be used with appropriate care for multiscale FEA simulations of composite materials. The largest error reported in this validation was in a four-point bend test specimen with an error of less than 1% difference in the maximum deflection of the beam

Economic valuation of the potential health benefits from foods enriched with plant sterols in Canada

Background: Increased consumption of foods containing plant sterols has the potential to reduce the incidence of coronary heart disease (CHD) and thus reduce costs associated with treating that disease in a significant way. This paper reports the results of an investigation of the potential monetary benefits of allowing foods enriched with plant sterols to be marketed in Canada. Objective: The objective of this research was to estimate the annual savings that would accrue to Canada's single-payer publicly funded health care system if plant sterols were approved for use. If foods containing plant sterols are consumed at a sufficient rate, a reduction in CHD should follow. Given the significant costs associated with CHD, approval of plant sterols in Canada has important public policy implications. Design: This research employs a variation of traditional cost-of-illness analysis entailing four steps: (1) estimation of a ‘success rate’ (proportion of persons who would consume plant sterols at the necessary rate); (2) presumption of blood cholesterol reduction due to plant sterol consumption; (3) assumption of reduction in CHD that follows from blood cholesterol reduction; and (4) calculation of cost savings associated with reduced incidence of CHD. Results: Calculations were carried out for four scenarios: ideal, optimistic, pessimistic, and very pessimistic. It was estimated that between $38 million (very pessimistic scenario) and $2.45 billion (ideal scenario) could be saved annually by Canada's health care system with plant sterol-enriched food products being made available for sale. Conclusion: Significant expenditure reductions within Canada's publicly funded health care system could be realized with plant sterols approved for sale. Reduced CHD resulting from lower blood cholesterol levels would lessen the financial burden of disease in Canada

Computational modeling of failure in composite structures including uncertainties in material and geometrical properties

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/90654/1/AIAA-2011-1722-752.pd

Pinyon and Juniper Encroachment into Sagebrush Ecosystems Impacts Distribution and Survival of Greater Sage-Grouse

AbstractIn sagebrush (Artemisia spp.) ecosystems, encroachment of pinyon (Pinus spp.) and juniper (Juniperus spp.; hereafter, “pinyon-juniper”) trees has increased dramatically since European settlement. Understanding the impacts of this encroachment on behavioral decisions, distributions, and population dynamics of greater sage-grouse (Centrocercus urophasianus) and other sagebrush obligate species could help benefit sagebrush ecosystem management actions. We employed a novel two-stage Bayesian model that linked avoidance across different levels of pinyon-juniper cover to sage-grouse survival. Our analysis relied on extensive telemetry data collected across 6 yr and seven subpopulations within the Bi-State Distinct Population Segment (DPS), on the border of Nevada and California. The first model stage indicated avoidance behavior for all canopy cover classes on average, but individual grouse exhibited a high degree of heterogeneity in avoidance behavior of the lowest cover class (e.g., scattered isolated trees). The second stage modeled survival as a function of estimated avoidance parameters and indicated increased survival rates for individuals that exhibited avoidance of the lowest cover class. A post hoc frailty analysis revealed the greatest increase in hazard (i.e., mortality risk) occurred in areas with scattered isolated trees consisting of relatively high primary plant productivity. Collectively, these results provide clear evidence that local sage-grouse distributions and demographic rates are influenced by pinyon-juniper, especially in habitats with higher primary productivity but relatively low and seemingly benign tree cover. Such areas may function as ecological traps that convey attractive resources but adversely affect population vital rates. To increase sage-grouse survival, our model predictions support reducing actual pinyon-juniper cover as low as 1.5%, which is lower than the published target of 4.0%. These results may represent effects of pinyon-juniper cover in areas with similar ecological conditions to those of the Bi-State DPS, where populations occur at relatively high elevations and pinyon-juniper is abundant and widespread