GUR1050 is a medical grade variety of ultra-high molecular weight polyethylene (UHMWPE) intended for use on total joint prosthesis and implants. Probes of this material were characterized on a compression test following ASTM norms and lineaments. Available data from these mechanical tests is fitted on multiple material models. Achieved results on numerical solutions of finite element modeling (FEM) of the tests are discussed, looking for the best one available in order to simulate with accuracy GUR1050 behavior, with specific interest on the load curve results, showing the pertinence of using certain models on different conditions. It was found that the use of a bilinear isotropic hardening model assures the best fit for GUR1050 behavior in uniaxial compression under a constant strain rate.

Background: Knot tying is considered a basic surgical skill, however, there is no consensus on the best technique. Suture breakage and slippage are failure modes during surgical repair and are related to stress concentrations which cannot be easily established with physical testing. Few computational models exist that describe the effect of knot topology on the failure mechanism. The purpose of this study was to implement the finite element method to analyze the mechanical behavior of surgical sutures according to number of throws and to validate the model against experiments. Methods: Experiments and models of monofilament and multifilament sutures were conducted. Multiple throw knots were tested to failure in a laboratory setting and with corresponding finite element models. Gross loads were compared when the knot reached a localized material yield stress in the model or when failure occurred in laboratory tests that have the same suture topology. Results: The results of laboratory tests and corresponding finite element models of single throw knots were compared and found to be well correlated and consistent with existing literature in strength prediction and failure location. Moreover, single throw knots have reduced failure strengths relative to non-knotted suture approximately by 120 N for both monofilament and multifilament sutures, respectively. Clinical Relevance: This paper describes a model which can describe the initial failure process leading to knot failure. In addition, the model can evaluate the effect of knot topology on the mechanics of surgical suture. Numerically, no assessment has been completed of knot security (i.e., how likely the knot is to untie), therefore, clinical recommendations are premature. In the future, the results may provide a framework for choosing the suture and knot types for soft tissue repairs.

Engineered tissue constructs are assembled through combining scaffolds, cells and biologically active molecules for restoring, maintaining, or improving damaged tissues or whole organs. Cells in engineered tissue constructs often experience mechanical forces during the fabrication process, maturation process, and under in vivo conditions. These mechanical forces/stimuli induce cellular responses and affect cell viability, proliferation, and differentiation. While it is critical to understand the mechanical milieu of cells in tissue constructs, it is also extremely challenging due to the time and length scale span. Multiscale modeling approaches have been emerged to provide linkage among different length scale. One of the approaches is continuum based multiscale modeling to link organ, tissue and cellular levels. A representative volume element (RVE) with periodic or random microstructure serves as a vehicle to connect different length scales. This study focuses on effects of RVE selection, microstructure, and boundary conditions on the mechanical environment at cellular level. In particular, cell embedded alginate tissue constructs were studied. Hyperelastic models were used for modeling alginate and cells. Multi-cellular FE models were generated. The results of the average properties and the stress/strain experienced by cells were compared under different conditions.

Background: Although trabecular bone is highly porous heterogeneous composite, most studies use homogenized continuum finite element (FE) approaches to model trabecular bone. Such models neglect the porous nature of the tissue. When microstructural models are desired, the use of continuum elements may require costly CT/MRI imaging and detailed meshing. The purpose of this study is to demonstrate an approach that simulates trabecular bone with less dependency on medical images while capturing of porosity. Methods: A stochastic structural FE model was created representing the trabecular micro-architecture as beam elements. Beam orientation, length and connectivity were stochastically determined by random placement of nodes and meshing the resulting Voronoi diagram. Boundary conditions were applied on the structure to attain normalized axial and shear strain. Also, apparent mechanical properties, apparent densities and anisotropy ratio’s were calculated from the model output. Results: The number of generated nodes within the model and cross sectional area of the random beams were observed as parameters that affect model outcome. Trabecular bone apparent density was found highly correlated to beams cross sectional area rather than the generated number of nodes. Similarly, Young’s moduli and shear moduli were dependent on beams cross sectional area. For example, a (0.015 mm 2 ) increase in beam cross section area can produce (175 MPa, 30 MPa and 0.55 g/cm 3 ) increases in Young’s moduli, shear moduli and apparent density, respectively. Clinical Relevance: The proposed finite element technique provides a stochastically accurate structural representation of trabecular tissue and its reaction to applied loads. It incorporates several advantages of high fidelity methods but at lower cost and requiring only clinical imaging. Therefore, the approach may be useful for patient specific musculo-skeletal biomechanical models (e.g. osteoporosis, osteoarthritis, joint replacement and implants interface).

Several types of implants, plates, and screws have been developed for corresponding bone fractures at different sites. To understand the mechanical behavior of a bone plate and to provide surgeons with suggestions for selecting screw positions, this study aimed to create an APP to provide pre-surgical planning using a computed tomography (CT)-based finite element model. This model was validated using a compression test of synthetic sawbones. Furthermore, the specific APP was established using the COMSOL application builder to calculate the stress and strain of the implant under different screw positions. This APP reveals how the number and location of screws affect the stress distribution of the implant. It can provide clinicians with preliminary reference information before surgery.

Accurate material properties of the brain and skull are needed to examine the biomechanics of head injury during highly dynamic loads such as blunt impact or blast. In this paper, a validated Finite Element Model (FEM) of a human head is used to study the biomechanics of the head in impact and blast leading to traumatic brain injuries (TBI). We simulate the head under various direction and velocity of impacts, as well as helmeted and un-helmeted head under blast waves. It is shown that the strain rates for the brain at impacts and blast scenarios are usually in the range of 36 to 241 s −1 . The skull was found to experience a rate in the range of 14 to 182 s −1 under typical impact and blast cases. Results show for impact incidents the strain rates of brain and skull are approximately 1.9 and 0.7 times of the head acceleration. Also, this ratio of strain rate to head acceleration for the brain and skull was found to be 0.86 and 0.43 under blast loadings. These findings provide a good insight into measuring the brain tissue and cranial bone, and selecting material properties in advance for FEM of TBI.

The aim of this study was to develop a test method to characterize the material behavior of bovine brain samples in large shear deformations and high strain rates relevant to blast-induced neurotrauma (BINT) and evaluate tissue damage. A novel shear test setup was designed and built capable of applying strain rates ranging from 300 to 1000 s −1 . Based on the shear force time history and propagation of shear waves, it was found that the instantaneous shear modulus (about 6 kPa) was more than 3 times higher than the values previously reported in the literature. The shear wave velocity was found to be strain path dependent which is an indication of tissue damage at strains greater than 10%. The results of this study can help in improving finite element models of the brain for simulating tissue injury during BINT.

This paper presents a systematic numerical investigation of guided wave generation, propagation, interaction with damage, and reception in anisotropic piezoelectric composite plates. This approach employs piezoelectric composite materials as both load bearing and sensing elements. Finite element modal analysis of a plate unit cell with Bloch-Floquet boundary condition is performed to understand the guided wave propagation characteristics in piezoelectric composite plates. The guided wave generation and tuning characteristics are investigated using the harmonic analysis model with absorbing boundary conditions. The relationship between the generated wave modes and the laminate layup orientations is studied. Subsequently, an impact damage is introduced and modeled as a group of cone shape delaminated layers and stiffness losses within the layers through the thickness direction. 2D and 3D transient dynamic coupled-field finite element models are constructed to simulate the procedure of guided wave generation, propagation, interaction with the impact damage, and reception in an orthotropic piezoelectric composite plate using the commercial finite element software (ANSYS). In addition, Contact Acoustic Nonlinearity (CAN) is simulated via time domain transient analysis. Advanced signal processing techniques are used to extract the distinctive nonlinear features. The frequency-wavenumber analysis is further adopted to decipher wave modes and frequency components in the scattered wave field. This paper finishes with concluding remarks and suggestions for future work.

Due to high stiffness/weight ratio, composite materials are widely used in aerospace applications such as motor case of rockets which can be regarded as a pressure vessel. The most commonly used method to manufacture the pressure vessels is the wet filament winding. However, the mechanical performance of a filament wound pressure vessel directly depends on the manufacturing process, manufacturing site environmental condition and material properties of matrix and fiber. The designed ideal pressure vessel may not be manufactured because of the mentioned issues. Therefore, manufacturing of filament wound composite structures are based on manufacturing experience and experiment. In this study, the effect of layer-by-layer thickness and fiber volume fraction variation due to manufacturing process on the mechanical performance was investigated for filament wound pressure vessel with unequal dome openings. First, the finite element model was created for designed thickness dimensions and constant material properties for all layers. Then, the model was updated. The updated finite element model considered the layer-by-layer thickness and fiber volume fraction variation. Effects of the thickness and fiber volume fraction on the stress distribution along the motor axial direction were shown. Also hydrostatic pressurization test was performed to verify finite element analysis in terms of fiber direction strain through the motor case outer surface. Important aspects of analyzing a filament wound pressure vessel were addressed for designers.

In this paper, we have introduced a negative Dielectrophoresis based microfluidic system using a novel arrangement of microelectrodes to perform switching of micro objects. Both the experimental and numerical results are presented. Two sets of interdigitated electrodes, extending slightly into the microchannel from each sidewall, are embedded on the bottom of the microchannel. A finite element model in COMSOL Multiphysics 5.2a was developed to demonstrate switching of Red Blood Cells in the microchannel followed by multiple parametric studies to study the effect of several parameters on cell trajectories and optimize the design parameters. To verify numerical results, a PDMS-based microfluidic device on glass wafer was fabricated. The switching of Red Blood Cells in the microfluidic device with a single inlet and three outlets was also demonstrated.

Nowadays, many surface sensing mechanisms exist, not all of them can be applied in water-based environment. Most of surface sensing techniques were developed in air-based environment. In order to obtain a potential cell-based biosensor, the sensing method needs to be reliable and repeatable in liquid environment. Therefore, we adapt existing air-based surface acoustic sensor and promote the technology into water-based applications. The goal of this study is to apply surface acoustic waves (SAW) for water-based environment sensing. We will use shear horizontal wave (SH wave) as surface sensing mechanism. SH wave is a type of surface acoustic waves (SAW) which can be used for weight/mass sensing in the air environment. Interdigitated transducers (IDTs) induce the deformation of an ST-cut quartz crystal substrate in AC source and generate waves. With a thin layer of polymer like Parylene and polyimide, the SH wave will be confined between the interface of substrate and polymer layer without suffering the energy loss due to the liquid damping from above. The fundamental frequency of the SAW device is defined by the spacing between the electrodes of IDT. The frequency of interests for this research is below 100 MHz in water-based environment. Due to the stable frequency characteristics of ST-cut quartz in room temperature, this SAW device can be a good candidate for field applications. From an early IDTs design, investigation in material and IDTs configuration is necessary to improve signal quality in order to qualify for liquid phase cell-based bio-sensing applications. A simplified 3D unit cell FEM model is created to study the thickness effects of wave-guide and electrodes. Boundary conditions and assumptions are discussed in the modeling. The simulated eigenfrequency of SH mode is close to the theoretical fundamental frequency of the 64μm wavelength IDTs. The mass damping effects from gold electrodes is more significant than aluminum electrodes.

In the Suspended ThermoReflectance (STR) technique a microcantilever is heated with a laser power at the free end of the microcantilever and as heat propagates through it, another laser is used to measure the temperature along the beam.[1] In this paper, the heat equation is solved for two-dimensional heat flow in the microcantilever to determine the material’s thermal conductivity and heat capacity. Two of the dimensions of the microcantilever, width and length, are significantly greater than the third dimension, the thickness, leading to the two-dimensional approximation. Two boundaries along the length of the structure and one boundary along the width are assumed to be under Dirichlet boundary conditions, while the other boundary has Neumann condition. The Neumann or flux condition has a Gaussian profile due to the nature of laser beam intensity. The heat equation is solved using under 3 different flux conditions: (1) Steady-state, (2) Transient, and (3) Periodic. A steady-state condition mimics the experimental condition when a continuous wave laser is used to heat the microcantilever’s tip. A transient condition is possible when quickly removing or adding the continuous wave laser’s flux from the microcantilever’s tip using a chopper. Finally, a periodic condition can be achieved when an electro-optic modulator is utilized experimentally. Closed form analytical expressions are evaluated against the finite element model and experimental results for microcantilever beams and micro-structures of Si that have lengths on the order of a mm, width on the order of 100 microns, and thicknesses of 1 micron or less.

This work will demonstrate the development and experimental validation of the stochastic models to predict the composite material’s mechanical and electromagnetic response as a function of the constituent reinforcing materials. First, stochastic micromechanics models will be developed for the case of multiple disparate supporting materials. These micromechanics models will then be validated against traditional finite element models and experimental results over the feasible parameter space. The developed models will then be utilized to define the optimal geometry of the composite flywheel including constraints such as displacement, stress, flux, magnetic field density, and manufacturability.

The appearance of cracks in rotor systems affects the whirl response in the neighborhood of the critical whirl rotational speeds. The combined effect of the crack depth and the unbalance force vector angle orientation with respect to the crack opening direction on the effective stiffness content of the cracked rotor system in the neighborhood of the critical rotational speed is addressed here. The effective stiffness expression of the cracked system can be obtained from the direct integration of the equations of motion of the cracked rotor system. The cracked rotor equations of motion can be expressed by the Jeffcott rotor or the finite element models. The appearance of cracks in rotor systems converts them into parametrically excited dynamical systems with time-periodic stiffness components. The interaction between the time-periodic stiffness and the external periodic forcing function of the unbalance force significantly alters the effective stiffness content in the system at both transient and steady state operations. For wide range of crack depths and unbalance force vector angles, the effective stiffness has been found to be of negative values. This means that the cracked rotor system tends to have more resistance to deflect towards the center of its whirl orbit and less resistance to deflect away under the unbalance force excitation effect. Consequently, in the negative stiffness content zone of the unbalance force vector angles, the cracked rotor system tends to exhibit a sharp growth in the vibration whirl amplitudes. However, for positive effective stiffness values, the shaft has more resistance to deflect away from its whirl orbit center. Therefore, the cracked rotor system is at higher risk of failure in the negative effective stiffness zone of unbalance force vector angles than the positive effective stiffness zone of these angles.

Hydroplaning is a phenomenon which occurs when a layer of water between the tire contact patch and pavement pushes the tire upward. The tire detaches from the pavement, preventing it from providing sufficient forces and moments for the vehicle to respond to driver’s control inputs such as breaking, acceleration and steering. This work is mainly focused on the tire and its interaction with the pavement to address hydroplaning. Fluid Structure Interactions (FSI) between the tire-water-road surfaces are investigated through two approaches. In the first approach, the coupled Eulerian-Lagrangian (CEL) formulation was used. The drawback associated with the CEL method is the laminar assumption and that the behavior of the fluid at length scales smaller than the smallest element size is not captured. As a result, in the second approach, a new Computational Fluid Dynamics (CFD) Fluid Structure Interaction (FSI) model utilizing the shear-stress transport k-ω model and the two-phase flow of water and air, was developed that improves the predictions with real hydroplaning scenarios. Review of the public literature shows that although FEM and CFD computational platforms have been applied together to study tire hydroplaning, developing the tire-surrounding fluid flow CFD model using Star-CCM+ has not been done. This approach, which was developed during this research, is explained in details and the results of hydroplaning speed and cornering force from the FSI simulations are presented and validated using the data from literature.

There are many models of impact used to predict the post-impact conditions of a system and all of them are based on Hertz’s theory, dated from the nineteenth century, where the repulsive force is proportional to the deformation of the bodies under contact and may also be proportional to the rate of deformation. The objective of this work is to analyze the behavior of the bodies during impact using some contact models and compare the results to a Finite Element Method model. The main parameters which will be evaluated are the body velocities, the contact force and the deformation of the bodies. An advantage of using the Finite Element Method is the possibility to apply plastic deformation to the model according to material definition. In the present study, it will be used Johnson–Cook plasticity model where the parameters are obtained based on empirical tests of real materials. Thus, it is possible to compare the behavior of elastic and plastic numerical models with the finite element model and to verify how these models reproduce the impact between solid bodies.

In the present paper, the load factor for bolted T-shape flange joints where two dissimilar material (steel-aluminum) of T-shape flanges are clamped by two bolts and nuts under external tensile loadings is examined using Finite Element analysis. Furthermore, the effect of the distance C between the center of the bolt and that of T-shape flange on the load factor and a load when the interfaces start to separate are examined. In addition, the mechanical characteristics of bolted T-shape flange joints where two clamped parts are steel and aluminum are examined. The value of the load factor for steel-aluminum T-flange joint is a little bit larger than that for steel-steel T-flange joints. When the external tensile loads are applied to the bolted T-shape flange joints, the bolts are inclined and as a result, the bending moment occurs in the bolts. A maximum bending stress in the bolts is also shown and it is about 6% larger than the bolt stress due to the load factor. For verification of FEM calculations, experiments to measure the load factor and the maximum bending stress occurred in the bolts are carried out. The FEM results are in a fairly good agreement with the experimental results. Finally, based on the obtained results, a design method for bolted joints with dissimilar T-shape flanges is demonstrated for determining the nominal bolt diameter and the bolt strength grade. It is found that the contact stress at the bearing surfaces of aluminum T-flange is critical.

Polycarbonate glass is one of the most widely used materials in the optical industries for making impact resistance lenses. Besides optical applications, polycarbonate glass has found applications in automotive and biomedical industries. The objective of this study is to investigate the effect of tool coating on the reduction of tool wear and cutting forces during micro-milling of polycarbonate glass. Both numerical modeling and experimental investigation have been carried out to investigate the effectiveness of various tool coatings on the carbide tool in minimizing the cutting forces, and hence tool wear. A series of experiments were conducted using CNC micro-milling of polycarbonate glass by varying feed rate, depth of cut, and tool coating. The three types of cutting tools used in this study were uncoated, titanium nitride (TiN) coated, and titanium aluminum nitride (TiAlN) coated tungsten carbide tools. The cutting forces have been recorded using the Kistler force dynamometer and the tool wear were analyzed using scanning electron microscope (SEM). It was found that all tools had reduced instances of failure, chipping, and abrasion at a moderately higher feed rate and depth of cut. Both very low and high feed rate were found to result in comparatively higher tool wear. The cutting forces increased with an increase of depth of cut, except for the TiAlN coated tool in some instances. With the increase of feed rate, the cutting forces gradually increased or stayed relatively constant across all depths of cut. It was found that the TiAlN coated tool reduced the amount of tool wear and cutting force across all feed rates and depths of cut. There is also a critical depth of cut around 0.3–0.5 mm and feed rate around 576–768 mm/min that reduced the amount of tool wear for the micro-milling of polycarbonate glass. Finally, the numerical modeling and simulation results of cutting forces were found to be in good agreement with the experimental cutting forces and the validated FEM models were then used to predict the cutting forces for higher spindle speed.

The aim of this study is mainly about preventing crack initiation and propagation in rolling contact under moderate and extreme loading through coating technology using finite element simulation and design of experiment (DOE) optimization techniques. Several applications of rolling contact were conducted and the parameters related to rollers’ materials, coating, temperature, and loads were investigated. M50 steels (0.8C-4.2Cr-4.3Mo-1V wt.%) and 100CrMnMo8 steel (1.0C-2.0Cr-0.5Mo-1.0Mn-0.5Si wt.%) were analyzed with and without titanium nitride (TiN), zirconium nitride (ZrN) and tungsten carbide (WC) coatings under different temperature and loading conditions. Results showed that cracks propagation were limited to extreme load when using coating technology. A fully three-dimensional finite element model showed the Von Mises stresses and displacement under different temperatures. Findings confirmed that coating will enhance the lifetime of rollers and inhibit cracks and plastic deformation with better contribution from TiN under extreme pressure if compared to WC. DOE optimization of the parameter used in this study correlate closely with previous experiments and provided a solid conclusion of the best combination in rolling contact applications.

The properties of the inclusions, viz. size, shape, and distribution significantly affect macroscopic properties of a polymer composite. Finite element (FE) modeling provides a viable approach for investigating the effects of the inclusions on the macroscopic properties of the polymer composite. In this paper, finite element method is used to investigate ultrasonic wave propagation in polymer matrix composite with a dispersed phase of inclusions. The finite element models are made up of three phases; viz. the polymer matrix, inclusions (micro constituent), and interphase zones between the inclusions and the polymer matrix. The analysis is performed on a three dimensional finite element model and the attenuation characteristics of ultrasonic longitudinal waves in the matrix are evaluated. The attenuation in polymer composite is investigated by changing the size, volume fraction of inclusions, and addition of interphase layer. The effect of loading frequency of the wave on the attenuation characteristics is also studied by varying the frequency in the range of 1–4 MHz. Results of the test revealed that higher volume fraction of inclusions gave higher attenuation in the polymer composite as compared to the lower volume fraction model. Smaller size of inclusions are preferred over larger size as they give higher wave attenuation. It was found that the attenuation characteristics of the polymer composite are better at higher frequencies as compared to lower frequencies. It is also concluded that the interphase later plays a significant role in the attenuation characteristics of the composite.