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Full-Text Articles in Engineering
On The Uniqueness And Sensitivity Of Indentation Testing Of Isotropic Materials, J. K. Phadikar, T. A. Bogetti, Anette M. Karlsson
On The Uniqueness And Sensitivity Of Indentation Testing Of Isotropic Materials, J. K. Phadikar, T. A. Bogetti, Anette M. Karlsson
Mechanical Engineering Faculty Publications
Instrumented indentation is a popular technique to extract the material properties of small scale structures. The uniqueness and sensitivity to experimental errors determine the practical usefulness of such experiments. Here, a method to identify test techniques that minimizes sensitivity to experimental erros is in indentation experiments developed. The methods are based on considering “shape functions,” which are sets of functions that describe the force–displacement relationship obtained during the indentation test. The concept of condition number is used to investigate the relative reliability of various possible dual indentation techniques. Interestingly, it was found that many dual indentation techniques can be as …
Implementation Of A Plastically Dissipated Energy Criterion For Three Dimensional Modeling Of Fatigue Crack Growth, Parag G. Nittur, Anette M. Karlsson, Leif A. Carlsson
Implementation Of A Plastically Dissipated Energy Criterion For Three Dimensional Modeling Of Fatigue Crack Growth, Parag G. Nittur, Anette M. Karlsson, Leif A. Carlsson
Mechanical Engineering Faculty Publications
Fatigue crack growth is simulated using three dimensional elastic-plastic finite element analysis. The crack extension per load cycle, da/dN, as well as crack front profile changes (crack tunneling) under cyclic loading is not specified as an input but evaluated based on a condition that relates plastically dissipated energy to a critical value. Simulation of cyclic crack propagation in a middle-crack tension M(T) specimen using this implementation captures the well established, experimentally obtained crack growth rate reduction accompanying a single overload event. The analysis predicts that the single overload also affects the crack front profile, where a tunneling crack propagates with …
Conical Indentation Of A Viscoelastic Sphere, J. K. Phadikar, T. A. Bogetti, V. N. Kaliakin, Anette M. Karlsson
Conical Indentation Of A Viscoelastic Sphere, J. K. Phadikar, T. A. Bogetti, V. N. Kaliakin, Anette M. Karlsson
Mechanical Engineering Faculty Publications
Instrumented indentation is commonly used for determining mechanical properties of a range of materials, including viscoelastic materials. However, most—if not all—studies are limited to a flat substrate being indented by various shaped indenters (e.g., conical or spherical). This work investigates the possibility of extending instrumented indentation to nonflat viscoelastic substrates. In particular, conical indentation of a sphere is investigated where a semi-analytical approach based on “the method of functional equations” has been developed to obtain the force–displacement relationship. To verify the accuracy of the proposed methodology selected numerical experiments have been performed and good agreement was obtained. Since it takes …
Time-Dependent Mechanical Response Of A Composite Pfsa Membrane, Narinder S. Khattra, Zongwen Lu, Anette M. Karlsson, Michael H. Santare, F. Colin Busby, Thomas Schmiedel
Time-Dependent Mechanical Response Of A Composite Pfsa Membrane, Narinder S. Khattra, Zongwen Lu, Anette M. Karlsson, Michael H. Santare, F. Colin Busby, Thomas Schmiedel
Mechanical Engineering Faculty Publications
The mechanical response of a composite fuel cell membrane, made from layers of reinforced and unreinforced PFSA material, is investigated via both experimental and numerical means. First, the time-dependent mechanical properties for the reinforced layers are measured for a range of environmental and loading conditions. A three-network, viscoelastic-plastic constitutive model is developed to characterize the mechanical response of this reinforced membrane material. This constitutive model is then used in finite element simulations of a fuel cell unit (consisting of composite membrane, electrodes, gas diffusion layer and bipolar plates) where the effect of relative humidity (RH) cycling on the stress response …
In Situ Analysis Of Fatigue Crack Propagation In Polymer Foams, Elio E. Saenza, Leif A. Carlsson, Anette M. Karlsson
In Situ Analysis Of Fatigue Crack Propagation In Polymer Foams, Elio E. Saenza, Leif A. Carlsson, Anette M. Karlsson
Mechanical Engineering Faculty Publications
This paper presents an in situ SEM experimental study on cyclic crack propagation in closed-cell polymer foams. The microscopic failure mechanisms in precracked PVC and PES specimens of 60 and 90 kg/m3 densities were examined under low-cycle fatigue loading. In the PVC foam, crack propagation occurred incrementally by successive failure of cell boundaries in front of the crack tip. The crack occasionally jumped to cell boundaries above or below the main crack resulting in non-self similar growth. Crack propagation in the PES foam occurred incrementally by extensive plastic tearing and subsequent tensile failure of the cell edge in front …
Biogeography-Based Optimization For Hydraulic Prosthetic Knee Control, Tim Wilmot, George Thomas, Berney Montavon, Rick Rarick, Antonie J. Van Den Bogert, Steve Szatmary, Daniel J. Simon, William Smith, Sergey Samorezov
Biogeography-Based Optimization For Hydraulic Prosthetic Knee Control, Tim Wilmot, George Thomas, Berney Montavon, Rick Rarick, Antonie J. Van Den Bogert, Steve Szatmary, Daniel J. Simon, William Smith, Sergey Samorezov
Electrical and Computer Engineering Faculty Publications
We discuss open-loop control development and simulation results for a newly-developed cyber-physical system (CPS) used as a semi-active, above-knee prosthesis. The control signal of our CPS consists of two hydraulic valve settings that control a linear cylinder actuator and provide torque to the prosthetic knee. We develop open-loop control using biogeography-based optimization (BBO), which is a recently developed evolutionary algorithm. The research contributes to the field of cyber-physical systems by showing that it is possible to find effective open-loop control signals for our newly proposed semi-active hydraulic knee prosthesis through a dual-system optimization process which includes both human and robot …