Elastic-Plastic Finite Element Analysis of Fatigue Crack Growth in Mode 1 and Mode 2 Conditions

Presented is an alternate cost-efficient and accurate elastic-plastic finite element procedure to analyze fatigue crack closure and its effects under general spectrum loading. Both Modes 1 and 2 type cycling loadings are considered. Also presented are the results of an investigation, using the newly developed procedure, of various factors that cause crack growth acceleration or retardation and delay effects under high-to-low, low-to-high, single overload, and constant amplitude type cyclic loading in a Mode 1 situation. Further, the results of an investigation of a centercracked panel under external pure shear (Mode 2) cyclic loading, of constant amplitude, are reported

Creep crack-growth: A new path-independent T sub o and computational studies

Two path independent integral parameters which show some degree of promise as fracture criteria are the C* and delta T sub c integrals. The mathematical aspects of these parameters are reviewed. This is accomplished by deriving generalized vector forms of the parameters using conservation laws which are valid for arbitrary, three dimensional, cracked bodies with crack surface tractions (or applied displacements), body forces, inertial effects and large deformations. Two principal conclusions are that delta T sub c is a valid crack tip parameter during nonsteady as well as steady state creep and that delta T sub c has an energy rate interpretation whereas C* does not. An efficient, small displacement, infinitestimal strain, displacement based finite element model is developed for general elastic/plastic material behavior. For the numerical studies, this model is specialized to two dimensional plane stress and plane strain and to power law creep constitutive relations

Creep crack-growth: A new path-independent integral (T sub c), and computational studies

The development of valid creep fracture criteria is considered. Two path-independent integral parameters which show some degree of promise are the C* and (Delta T)sub c integrals. The mathematical aspects of these parameters are reviewed by deriving generalized vector forms of the parameters using conservation laws which are valid for arbitrary, three dimensional, cracked bodies with crack surface tractions (or applied displacements), body forces, inertial effects, and large deformations. Two principal conclusions are that (Delta T)sub c has an energy rate interpretation whereas C* does not. The development and application of fracture criteria often involves the solution of boundary/initial value problems associated with deformation and stresses. The finite element method is used for this purpose. An efficient, small displacement, infinitesimal strain, displacement based finite element model is specialized to two dimensional plane stress and plane strain and to power law creep constitutive relations. A mesh shifting/remeshing procedure is used for simulating crack growth. The model is implemented with the quartz-point node technique and also with specially developed, conforming, crack-tip singularity elements which provide for the r to the n-(1+n) power strain singularity associated with the HRR crack-tip field. Comparisons are made with a variety of analytical solutions and alternate numerical solutions for a number of problems

Stress and Fracture Analyses Under Elastic-plastic and Creep Conditions: Some Basic Developments and Computational Approaches

A new hybrid-stress finite element algorith, suitable for analyses of large quasi-static deformations of inelastic solids, is presented. Principal variables in the formulation are the nominal stress-rate and spin. A such, a consistent reformulation of the constitutive equation is necessary, and is discussed. The finite element equations give rise to an initial value problem. Time integration has been accomplished by Euler and Runge-Kutta schemes and the superior accuracy of the higher order schemes is noted. In the course of integration of stress in time, it has been demonstrated that classical schemes such as Euler's and Runge-Kutta may lead to strong frame-dependence. As a remedy, modified integration schemes are proposed and the potential of the new schemes for suppressing frame dependence of numerically integrated stress is demonstrated. The topic of the development of valid creep fracture criteria is also addressed

Stress-intensity factors for small surface and corner cracks in plates

Three-dimensional finite-element and finite-alternating methods were used to obtain the stress-intensity factors for small surface and corner cracked plates subjected to remote tension and bending loads. The crack-depth-to-crack-length ratios (a/c) ranged from 0.2 to 1 and the crack-depth-to-plate-thickness ratios (a/t) ranged from 0.05 to 0.2. The performance of the finite-element alternating method was studied on these crack configurations. A study of the computational effort involved in the finite-element alternating method showed that several crack configurations could be analyzed with a single rectangular mesh idealization, whereas the conventional finite-element method requires a different mesh for each configuration. The stress-intensity factors obtained with the finite-element-alternating method agreed well (within 5 percent) with those calculated from the finite-element method with singularity elements

HIV and Cocaine Impact Glial Metabolism: Energy Sensor AMP-activated protein kinase Role in Mitochondrial Biogenesis and Epigenetic Remodeling

HIV infection and cocaine use have been identified as risk factors for triggering neuronal dysfunction. In the central nervous system (CNS), energy resource and metabolic function are regulated by astroglia. Glia is the major reservoir of HIV infection and disease progression in CNS. However, the role of cocaine in accelerating HIV associated energy deficit and its impact on neuronal dysfunction has not been elucidated yet. The aim of this study is to elucidate the molecular mechanism of HIV associated neuropathogenesis in cocaine abuse and how it accelerates the energy sensor AMPKs and its subsequent effect on mitochondrial oxidative phosphorylation (OXPHOS), BRSKs, CDC25B/C, MAP/Tau, Wee1 and epigenetics remodeling complex SWI/SNF. Results showed that cocaine exposure during HIV infection significantly increased the level of p24, reactive oxygen species (ROS), ATP-utilization and upregulated energy sensor AMPKs, CDC25B/C, MAP/Tau and Wee1 protein expression. Increased ROS production subsequently inhibits OCR/ECAR ratio and OXPHOS, and eventually upregulate epigenetics remodeling complex SWI/SNF in CHME-5 cells. These results suggest that HIV infection induced energy deficit and metabolic dysfunction is accelerated by cocaine inducing energy sensor AMPKs, mitochondrial biogenesis and chromatin remodeling complex SWI/SNF activation, which may lead to neuroAIDS disease progression

Effects of Diabetes on pulmonary function tests in COPD Patient

COPD (chronic obstructive pulmonary disease) is a condition caused by abnormalities in the inflammatory responses of the lungs to irritable particles or gases. This is an irreversible condition that progresses in later years.Diabetes patients have an increased risk of developing abnormal lung functioning and also in conditions of COPD it even worsens the condition, up to 1.6-16% of the COPD population were affected due to diabetes mellitus.Many studies also suggest that the lungs are a target organ in diabetes and glycemic exposure may be a causation factor for reduced lung function. Systemic inflammation, hypoxemia, oxidative stress, altered gas exchange, and changes in lung tissues were the major impacts on the respiratory system which were induced by hypoglycemia. In this study, we aimed to assess the lung functioning in COPD patients with diabetes by performing the pulmonary functions test like spirometry by obtaining the values of FVC, FEV1, FEV/FVC, and PEF thereby analyzing the level of lung dysfunction that has been done. Patients were includes of both genders and were divided into two groups depending on their disease group 1 includes COPD and group 2 includes COPD with DM considering twenty members in each group. Our study results show that diabetes worsens the lung functioning in COPD than it already is, it may also cause respiratory collapse if untreated

Multi Response Optimization of Setting Input Variables for Getting Better Product Quality in Machining of Magnesium AM60 by Grey Relation Analysis and ANOVA

This study presents the optimization of Machining parameters on AM60 Mg alloy manufactured by Gravity Die Casting and with responses supported orthogonal array with Grey relation analysis. Focuses on the optimization of Machining input parameters using the technique to get minimum surface roughness, Minimum Tool Wear, Cutting Time, Power Requirement, Torque and Maximum MRR. A number of Machining trails were conducted based on the L9 orthogonal array on CNC machine. The experiments were performed on AM60 alloy using cutting tool of an ISO 460.1-1140-034A0-XM GC3 of 12,16 and 25 mm diameter with cutting point 140 degrees, throughout the experimental work under different cutting conditions. Grey relation analysis & ANOVA were used to work out the fore most important parameters Cutting speed, feed rate, Depth of Cut and Tool Diameter which affects the Response. The expected response and measured response are fairly close. The given model could be used to select the level of Machining parameters