Enhancement of Bone Implants by Substituting Nitinol for Titanium (Ti-6Al-4V): A Modeling Comparison

Mandibular segmental defect reconstruction is most often necessitated by tumor resection, trauma, infection, or osteoradionecrosis. The standard of care treatment for mandibular segmental defect repair involves using metallic plates to immobilize fibula grafts, which replace the resected portion of mandible. Surgical grade 5 titanium (Ti-6Al-4V) is commonly used to fabricate the fixture plate due to its low density, high strength, and high biocompatibility. One of the potential problems with mandibular reconstruction is stress shielding caused by a stiffness mismatch between the Titanium fixation plate and the remaining mandible bone and the bone grafts. A highly stiff fixture carries a large portion of the load (e.g., muscle loading and bite force), therefore the surrounding mandible would undergo reduced stress. As a result the area receiving less strain would remodel and may undergo significant resorption. This process may continue until the implant fails. To avoid stress shielding it is ideal to use fixtures with stiffness similar to that of the surrounding bone. Although Ti-6Al-4V has a lower stiffness (110 GPa) than other common materials (e.g., stainless steel, tantalum), it is still much stiffer than the cancellous (1.5–4.5 GPa) and cortical portions of the mandible (17.6–31.2 GPa). As a solution, we offer a nitinol in order to reduce stiffness of the fixation hardware to the level of mandible. To this end, we performed a finite element analysis to look at strain distribution in a human mandible in three different cases: I) healthy mandible, II) resected mandible treated with a Ti-6Al-4V bone plate, III) resected mandible treated with a nitinol bone plate. In order to predict the implant’s success, it is useful to simulate the stress-strain trajectories through the treated mandible. This work covers a modeling approach to confirm superiority of nitinol for mandibular reconstruction. Our results show that the stress-strain trajectories of the mandibular reconstruction using nitinol fixation is closer to normal than if grade 5 surgical titanium fixation is used.

Dynamic Characteristics Analysis of a Silicon Pressure Sensor Using Network Methods

This paper presents a method to describe electromechanical systems with an equivalent network description for an early investigation of the dynamical behavior during the design process. The procedure using equivalent circuits modeling for system description is outlined with an example of characterizing a silicon pressure sensor for a first analysis of its transmission behavior. Therefore, the sensor is separated into acoustic and mechanical systems of the casing and electromechanical systems of the silicon element. Friction, compliance and mass of the diaphragm for the pressure application are modeled in the mechanical domain using the equivalent electrical symbols of resistance, inductance and capacity. The pressure transmission with a filling fluid in a canal is modeled using acoustic parameters. The solution of the transfer function enables an analysis of the amplitude frequency response between the acoustic, mechanical and electric systems of the sensor. A first comparison between simulation and measurement results shows a correlation in the pressure transfer function of the silicon sensor.

Phenomenological Models of Solid State Actuators for Network Based System Modelling

Smart materials, such as thermal or magnetic shape memory alloys, provide interesting characteristics for new solid state actuators. However, their behavior is highly nonlinear and determined by strong hysteresis effects. This complex behavior must be adequately considered in simulation models which can be applied for efficient actuator design and optimization. We present a new phenomenological lumped element model for magnetic shape memory alloys (MSM). The model takes into account the two-dimensional hysteresis of the magnetic field induced strain as a function of both the compressive stress and the magnetic flux density. It is implemented in Modelica. The model bases on measured limiting hysteresis surfaces which are material specific. An extended Tellinen hysteresis modeling approach is used to calculate inner hysteresis trajectories in between the limiting surfaces. The developed model provides sufficient accuracy with low computational effort compared to finite element models. Thus, it is well suited for system design and optimization based on network models. This is demonstrated with exemplary models of MSM based actuators. System models and simulation results are shown and evaluated for different topologies.

Modelling of Piezoceramic Patches for Actuator Placement Strategies

Piezoceramic Patches are commonly used as actuator devices in smart structures if the induced forces are sufficient for the application. To model these devices in a structural dynamics simulation, a finite element model can be augmented by active layers. This needs a suitable element meshing, taking care of the actual shapes and positions of the active patches in use. If many different setups have to be evaluated, which is naturally the case for placement strategies for suitable actuator positions, this approach is quite cumbersome. To ease and speed up the augmentation of fixed finite element models with piezoceramic patches, so called modal correction methods have been successfully used in this context. These approximative methods avoid the remeshing and the reassembling of the underlying finite element model by adapting the modal description of the structural model with the mass, stiffness and electrical coupling effects of the applied patches. In this paper different aspects of this modelling approach are discussed especially for a tool chain to optimize patch locations in an ASAC simulation environment.

Vibration Control of a New Bed Stage System for Ambulance Using MR Dampers

This paper proposes a new bed stage for patients in ambulance vehicle in order to improve ride quality in term of vibration control. The vibration of patient compartment in ambulance can cause a secondary damage to a patient and a difficulty for a doctor to perform emergency care. The bed stage is to solve vertical, rolling, and pitching vibration in patient compartment of ambulance. Four MR (magneto-rheological) dampers are equipped for vibration isolation of the stage. Firstly, a mathematical model of stage is derived followed by the measurement of vibration level of patient compartment of real ambulance vehicle. Then, the design parameters of bed stage is undertaken via computer simulation. Skyhook, PID and LQR controllers are used for vibration control and their control performances are compared.

Experimental Characterization of a Circular Diaphragm Dielectric Elastomer Generator

Inflated Circular Diaphragm Dielectric Elastomer Generators (CD-DEGs) are a special embodiment of polymeric transducer that can be used to convert pneumatic energy into high-voltage direct-current electricity. Potential application of CD-DEGs is as power take-off system for wave energy converters that are based on the oscillating water column principle. Optimal usage of CD-DEGs requires the adequate knowledge of their dynamic electro-mechanical response. This paper presents a test-rig for the experimental study of the dynamic response of CD-DEGs under different programmable electro-mechanical loading conditions. Experimental results acquired on the test-rig are also presented, which highlight the dynamic performances of CD-DEGs that are based on acrylic elastomer membranes and carbon conductive grease electrodes.

Adaptive Damage Detection Using Tunable Piezoelectric Admittance Sensor and Intelligent Inference

The piezoelectric impedance/admittance-based damage detection has been recognized to be sensitive to small-sized damage due to its high frequency measurement capability. Recently, a new class of admittance-based damage detection schemes has been proposed, in which the piezoelectric transducer is integrated with a tunable inductive circuitry. The present research focuses on exploiting the tunable nature of the piezoelectric admittance sensor for the effective identification of damage. In particular, we incorporate the Bayesian inference network into the damage detection process which can intelligently guide the accurate identification of damage location and severity by taking full advantage of the baseline model and measurement as well as the online measurement. As the tunable sensor can provide greatly enriched measurement information, the Bayesian inference can adequately utilize such information and furthermore directly and continuously update the structural model until the model prediction matches with the measurement results. This new approach takes into account the model uncertainty, measurement error, and incompleteness of measurements. Extensive numerical analyses and experimental studies are carried out on a panel structure for methodology demonstration and validation.

Time Integration and Assessment of a Model for Shape Memory Alloys Considering Multiaxial Nonproportional Loading Cases

The paper presents a numerical implementation of the ZM model for shape memory alloys that fully accounts for non-proportional loading and its influence on martensite reorientation and phase transformation. Derivation of the time-discrete implicit integration algorithm is provided. The algorithm is used for finite element simulations using Abaqus, in which the model is implemented by means of a user material subroutine. The simulations are shown to agree with experimental and numerical simulation data taken from the literature.

Visualization of Particle-Toughening Mechanism in Transparent Polyurethanes

Highly cross-linked polyurethanes have a high elastic modulus and creep resistance, but they undergo a brittle fracture below the glass transition temperature. Unfortunately, a large number of glassy polyurethanes are prone to brittle fracture without undergoing large elastic deformations; in particular, brittle failure is common under conditions such as low temperature and high strain rates. While the rigidity in polymers is required for practical applications, the lack of resistance against crack propagation is essential to avoid catastrophic failures. The toughening of polymers is a crucial aspect of improving the strength and ductility at specific temperatures and deformation rates. One method that has shown promise in recent years is the creation of local regions of reduced modulus that absorb strain energy and toughen the polymer. For instance, rubbers are typically added to epoxy which phase separate upon polymerization and create local elastic regions that significantly toughen the polymer. In this study, a variety of two-phase transparent polyurethanes in the form of single inclusions is designed to study the toughening mechanism of the local regions of reduced modulus with an embedded crack. Synthesized heterogeneous polyurethanes show a transition from brittle to ductile behavior in addition to a drastic increase in the maximum load that the polymer can withstand. Compact tension experiments demonstrate that a small reduction in the inclusion’s Young’s modulus (∼10%) leads to an increase in the toughness by factor of 7 (∼700%). Moreover, digital image correlation is performed to map the strain distribution around the crack in order to visualize possible toughening mechanism. Comparison between the induced strain field in samples with inclusion and samples without inclusion reveals an efficient toughening mechanism of the polymers.

A New Method for Coupling Transient Network Models and Stationary Finite-Element Models

In many cases, the accuracy of transient multi-domain network models can be improved by coupling to distributed models, e.g. finite-element (FE) models, which compute for specific element parameters, flow or potential variables of the network model. Two opposing methods are known. The first is direct simulator coupling. It requires solving of the distributed model in each iteration step of the network model simulation. The second is the uncoupled calculation of characteristic maps from stationary distributed models which are then used in the transient model in form of look-up tables. Since the course of the base parameters of the characteristic maps is unknown before the transient simulation runs the stationary distributed model has to be solved for all grid points of the spanned parameter space. Both methods lead to an inefficient high number of necessary calculations of the distributed model which usually determines the computing costs. We present a new approach which significantly reduces the number of necessary computations. The main idea is combining both methods and successively computing grid points of the characteristic maps depending on the current need while solving the transient model. This is demonstrated for the example of an electromagnetic actuator. In the presented example, the number of FE model calculations was reduced to a tenth.