A Methodology for Characterization of the Strain Rate-Dependent Behavior of PU Foam

Polymeric foams are known to be sensitive to strain rate under dynamic loads. Mechanical characterization of such materials would not thus be complete without capturing the effect of strain rate on their stress-strain behaviors. Consistent data on the dynamic behavior of foam is also necessary for designing energy-absorbing countermeasures based on foam such as for vehicle occupant safety protection. Strain rates of the order of 100-500 s−1 are quite common in such design applications; strain rates of this range cannot be obtained with an ordinary UTM (universal testing machine) and a special test set-up is usually needed. In the current study, a unique approach has been suggested according to which quasi-static tests at low strain rates and low velocity drop tests at medium strain rates are utilized to arrive at an empirical relation between initial peak stress and logarithm of strain rate for a rigid closed-cell PU foam. Using a stress-scaling methodology and the empirical relation mentioned, foam stress-strain curves are obtained for a number of strain rates spanning low (from 0.00033 s−1) to high strain rates (up to1000 s−1). This data on foam material behavior is expected to be particularly useful in numerical modelling of foam-based countermeasures for impact energy absorption applications

Adjacent Disc Stress Following Floating Lumbar Spine Fusion: A Finite Element Study

Study DesignExperimental study.PurposeThe study aimed to develop a finite element (FE) model to determine the stress on the discs adjacent to the fused segment following different types of floating lumbar spinal fusions.Overview of LiteratureThe quantification of the adjacent disc stress following different types of floating lumbar fusions has not been reported. The magnitude of the stress on the discs above and below the floating fusion remains unknown.MethodsA computer-aided engineering-based approach using implicit FE analysis was employed to assess the stress on the lumbar discs above and below the floating fusion segment (L4–L5) following anterior and posterior lumbar spine fusions at one, two, and three levels (with and without instrumentation).ResultsBoth discs suprajacent and infrajacent to the floating fusion experienced increased stress, but the suprajacent disc experienced relatively high stress level. Instrumentation increased the stress on the discs suprajacent and infrajacent to the floating fusion, but the magnitude of stress on the suprajacent disc remained relatively high.ConclusionsThe FE model was employed under similar loading and boundary conditions to provide quantitative data, which will be useful for clinicians to understand the probable long-term effects of floating fusions

Long-Term Effects of Segmental Lumbar Spinal Fusion on Adjacent Healthy Discs: A Finite Element Study

Study DesignExperimental study.PurposeThe aim of the study was to develop a finite element (FE) model to study the long-term effects of various types of lumbar spinal interventions on the discs adjacent to the fused segment.Overview of LiteratureEarlier FE studies have been limited to one particular type of fusion and comparative quantification of the adjacent disc stresses for different types of surgical interventions has not been reported.Methods A computer aided engineering (CAE) based approach using implicit FE analysis assessed the stresses in the lumbar discs adjacent to the fused segment following anterior and posterior lumbar spine fusions at one, two and three levels (with and without instrumentation).ResultsIt was found that instrumentation and length of fusion were the most significant factors in increasing adjacent level stresses in the lumbar discs.ConclusionsIn the present study, a calibrated FE model that examined spinal interventions under similar loading and boundary conditions was used to provide quantitative data which would be useful for clinicians to understand the probable long-term effect of their choice of surgical intervention

Is The Burden of Medical Education Affecting Ethics of Medical Treatment?

A substantial number of medical students in India have to bear an enormous financial burden for earning a bachelor's degree in medicine referred to as MBBS (bachelor of medicine and bachelor of surgery). This degree program lasts for four and one-half years followed by one year of internship. A postgraduate degree, such as MD, has to be pursued separately on completion of a MBBS. Every medical college in India is part of a hospital where the medical students get clinical exposure during the course of their study. All or at least a number of medical colleges in a given state are affiliated to a university that mainly plays a role of an overseeing authority. The medical colleges usually have no official interaction with other disciplines of education such as science and engineering, perhaps because of their independent location and absence of emphasis on medical research. However, many of the medical colleges are adept in imparting high-quality and sound training in medical practices including diagnostics and treatment. The medical colleges in India are generally of two types, i.e., government owned and private. Since only a limited number of seats are available across India in the former category of colleges, only a small fraction of aspiring candidates can find admission in these colleges after performing competitively in the relevant entrance tests. A major advantage of studying in these colleges is the nominal tuition fees that have to be paid. On the other hand, a large majority of would-be medical graduates have to seek admission in the privately run medical institutes in which the tuition and other related fees can be mind boggling when compared to their public counterparts. Except for candidates of exceptionally affluent background, the only alternative for fulfilling the dream of becoming a doctor is by financing one's study through hefty bank loans that may take years to pay back. It is often heard from patients that they are asked by doctors to undergo a plethora of diagnostic tests for apparently minor illnesses, which may financially benefit those prescribing the tests. The present paper attempts to throw light on the extent of disparity in cost of a medical education between state-funded and privately managed medical colleges in India; the average salary of a new medical graduate, which is often ridiculously low when compared to what is offered in entry-level engineering and business jobs; and the possible repercussions of this apparently unjust economic situation regarding the exploitation of patients

Finite element analysis of stiffened plates using Mindlin's theory

Finite element procedures based on Mindlin's theory are computationally advantageous and also have the capability of accounting for transverse shear deformation in plates. Complementary to Mindlin's theory is Timoshenko's theory that accounts for transverse shear deformation in beams. In the present work, both of these shear distortion theories have been applied to the finite element analysis of stiffened plates subjected to lateral loading. Discrete plate-beam formulations, termed FEM(Ml) and FEM(M2), have been set up illustrating two major approaches in the finite element analysis of stiffened plate structures. A third orthotropic formulation, named ORTHO, has been presented based on the smeared plate approach, and is applicable to the case of closely spaced torsionally soft stiffeners. The performance of the discrete plate-beam formulations, especially of the second viz. FEM(M2), has been found to be quite satisfactory based on a comparison with a number of the available results. For the first time an attempt has been made to estimate theoretically the errors that are likely to result from the use of an orthotropic formulation. This has been accomplished by comparison between ORTHO and FEM(M2) in the form of a parametric study. Additionally, the orthotropic formulation has been extended to include geometrically non-linear behaviour. It is recognised that under less demanding conditions this latter formulation may be preferable for the reasons of economy of CPU time and simplicity of input data

An Experimental Study on Energy Absorption Behavior of Polyurethane Foams

This article is concerned with a study on the energy absorption behavior of polyurethane (PU) foams such as flexible high resilience (HR), flexible viscoelastic (VE) and semi-rigid (SR) foams as a function of the overall foam density. Foam samples were prepared in the form of cubes by mixing appropriate polyol and isocyanate compounds produced by Huntsman International India Pvt. Ltd. in varying proportions leading to a range of densities for each type of foam. The cubical samples were tested under compressive load in a standard UTM. Based on the measured load-displacement behaviors, variations of peak load and energy-absorption attributes with respect to density are plotted for each type of foam and the possible existence of an optimum foam density is shown

Speed control of brushed DC motor for low cost electric cars

As petrol prices are going up in developing countries in upcoming decades low cost electric cars will become more and more popular in developing world. One of the main deciding factors for success of electric cars specially in developing world in upcoming decades will be its cost. This paper shows a cost effective method to control the speed of low cost brushed D.C. motor by combining a IC 555 Timer with a High Boost Converter. The main purpose of using High Boost Converter since electric cars needs high voltage and current which a High Boost Converter can provide even with low battery supply

EFFECT OF SITTING OCCUPANCY ON LATERAL DYNAMICS AND TRAJECTORY OF A PASSENGER CAR

In the current work, the effects of sitting locations and combinations of occupants on handling performance of a four wheeled passenger car have been investigated. A new multi occupant nonlinear lumped parameter model (LPM) is developed by coupling 1-DOF longitudinal vehicle model, 2-DOF lateral vehicle model, 13-DOF nonlinear vehicle ride model including seats, 6-DOF nonlinear human occupant model, and 1-DOF tire model. The combined model with a maximum of 50 degrees-of-freedom (in case of all five seats occupied) is simulated in MATLAB/SIMULINK environment. Model subsystems i.e. occupant and vehicle models including tires are validated independently by comparing biodynamic responses of seated occupants, vehicle vertical response and handling behavior with published results. The coupled model can facilitate the study of vehicle dynamics considering the combined effects of road inputs, vehicle maneuvering and seat occupancy while taking into account the nonlinear behavior of vehicle suspension. Further the yaw rate and vehicle trajectories are compared and studied for various cases of sitting occupancies at a given vehicle velocity with a road input representing harsh and abrupt scenario. The current study shows that appreciable changes in yaw rate and vehicle trajectory can be caused due to varying sitting occupancies and vehicle velocities

Evaluation of the accuracy of an impact load cell using lumped parameter modeling and analysis

The objective of the current study is to evaluate the fidelity of load cell reading during impact testing in a drop-weight impactor using lumped parameter modeling. For the most common configuration of a moving impactor-load cell system in which dynamic load is transferred from the impactor head to the load cell, a quantitative assessment is made of the possible discrepancy that can result in load cell response. A 3-DOF (degrees-of-freedom) LPM (lumped parameter model) is considered to represent a given impact testing set-up. In this model, a test specimen in the form of a steel hat section similar to front rails of cars is represented by a nonlinear spring while the load cell is assumed to behave in a linear manner due to its high stiffness. Assuming a given load-displacement response obtained in an actual test as the true behavior of the specimen, the numerical solution of the governing differential equations following an implicit time integration scheme is shown to yield an excellent reproduction of the mechanical behavior of the specimen thereby confirming the accuracy of the numerical approach. The spring representing the load cell, however,predicts a response that qualitatively matches the assumed load-displacement response of the test specimen with a perceptibly lower magnitude of load