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.

Detection and location of leaks in buried plastic fluid-filled pipes are topics of increasing concern for water distribution companies. Acoustic correlation techniques have been widely used to provide an accurate estimate of the position of a leak in order to reduce the wastage of water. However, this technique depends on an accurate estimate of the wave propagation speed along the pipe, which is heavily dependent on the type of soil in which the pipe is buried. The soil also affects the distance that leak noise will propagate along the pipe. This paper describes theoretical and experimental investigations into the way the coupling conditions between the pipe and the soil affects the propagation characteristics of the wave that propagates leak noise in the pipe. Two water pipe systems which have different soil properties are considered: one is in Brazil and the other one is in UK. For the Brazilian pipe system, it is found that the shear modulus rather than the bulk modulus of the soil, has a profound effect on the wave motion in the pipe since it is buried in a clay-like soil. In this case, only the shear wave in the soil propagates away from the pipe. For the UK pipe system, which has sandy soil, both compressional and shear waves propagate away from the pipe. An analysis of the physical effects of fluid-pipe-soil interface and their corresponding parameters on the pipe wave speed and attenuation is also carried out. The results show that the axial coupling between the pipe and the soil has an important effect in the UK pipe system, but has a negligible effect in the Brazilian pipe system.

Real-time inflow model for lifting rotor is required for pilot-in-the-loop simulation and flight control design. The recent developed blended inflow model have advanced the state-of-the-art with closed-form solution for all three components of the flow everywhere in the field, including below the plane of the rotor disk both in-wake and out-of-wake. The nonlinearity will be introduced in such blended model to make it more flexible not only for helicopter in cruise condition, but also for helicopter in low speed flight or hover. The dynamic loading for such inflow model will be computed in real-time based on blade element theory. Then the flap motions of blades of lifting rotor will be coupled, and the induced velocity will be solved numerically in the time domain through the simpletic scheme. A Harrington rotor will be studied as an example. The induced velocity in the time domain for such a rotor will be calculated with a specific flight controls.

A proximal femur fracture due to osteoporosis is one of serious health care problems in aging societies. Osteosynthesis with pin or screw type of implants, such as Hansson pin (HP), Dual SC Screw (DSCS), is widely used for femoral neck fracture treatment in Japan. Unfortunately, some complications such as secondary fractures, especially peri-prosthetic fractures, may occur during postoperative rehabilitation period. In order to reveal the potential cause of the postoperative fracture from the viewpoint of the biomechanics, authors had already performed the dynamic stress analysis of the treated proximal femur based on finite element (FE) analysis. The final goal of our project is to establish the reliable postoperative bone fracture risk assessment method in response to the daily activity including mainly walking. The aim of this study is to propose a novel elastic multi body analysis method based on FE analysis for proximal femur biomechanics. Patient-specific 3D left hip joint FE model was constructed from an elderly female volunteer’s CT images. The model consists of the pelvis, proximal femur, cartilage and DSCS, as multi bodies. The dynamic loading and boundary conditions were applied to the model for simulating a gait motion. Direction and magnitude of the loads varies in response to the gait motion. The time dependent loading forces; hip contact, gluteus medius, gluteus maximus, tensor fasciae latae and adductor, acting around the hip joint was obtained by inverse dynamic analysis of a human gait using in-house lower-limb musculoskeletal model. These loading and boundary conditions for simulating the gait motion are the major technical advantages of the proposed multi body analysis comparing with the conventional static FE analysis. Time varying stress distribution during the gait was evaluated by using dynamic explicit method via ABAQUS. In order to visually demonstrate dynamic stress distribution, we examined the time varying von Mises stresses at the representative points located on the cortical surface of the proximal femur; femoral head, fracture surface and around the lateral insertion holes. The results indicate significant increase of the stresses around the proximal lateral insertion holes for DSCS treatment. Maximum stress values are good agreement with the previous static FE analysis, on the other hand, these biomechanical discussions based on the stress time histories are only obtained from the proposed method. It is indicated that the proposed method is feasible to support the better pre- and postoperative clinical decisions, which is the main contribution of this study.

The objective of this study is to give an overview of existing theories for analyzing the behavior of sandwich beams and plates and to develop an approach for evaluating their behavior under dynamic loading. The dispersion relations for harmonic wave propagation through sandwich structures are shown to be a sound basis for evaluating whether the individual layers are modeled properly. The results provide a guide in the selection of existing models or the development of new models.

Injuries to the upper extremities that are caused by dynamic impacts in crashes, including contact with internal instrument panels, has been a major concern, especially for smaller female occupants, and the problem worsens with increasing age due to reduced strength of the bones. From the analysis of 1988–2010 CDS unweighted data, it was found that risk of AIS ≥ 2 level for the arm was 58.2±20.6 percent higher in females than males, and the injury risk for a 75-year-old female occupant relative to a 21-year-old subjected to a similar physical insult was 4.2 times higher. Although injuries to upper extremities are typically not fatal, they can have long-term effects on overall quality of life. Therefore, it is important to minimize risks of injuries related to upper extremities, especially for elderly females, who are most at risk. Current anthropomorphic surrogates, like crash-test dummies, cannot be directly used to study injury limits, as these dummies were developed mainly to represent the younger population. The current study is focused on the development of a finite element (FE) model representing the upper extremity of an elderly female. This can be further used to analyze the injury mechanisms and tolerance limits for this vulnerable population. The FE mesh was developed through Computer Tomography (CT) scanned images of an elderly female cadaver, and the data included for validation of the developed model were taken from the experimental studies published in scientific literature, but only the data directly representing elderly females were used. It was found that the developed model could predict fractures in the long bones of elderly female specimens and could be further used for analyzing injury tolerances for this population. Further, it was determined that the developed segmental model could be integrated with the whole body FE model of the elderly female.

This paper describes the development of a highly sensitive microfluidics flow sensor using MTJ magnetic sensors to detect motion of slow-moving fluids. A motivating application for the proposed device is the development of an implantable flow sensor, capable of monitoring the amount of cerebral spinal fluid drained from the ventricles of the brain. Micro-fabricated ferromagnetic flaps are used to detect motion of the surrounding fluid. The deflection of the flaps is detected by an ultra-sensitive MTJ magnetic field sensor placed outside of the lumen of the catheter. Previous studies have presented a working device with a resolution of up to 1.4 mL/hr. This paper presents the improvements made to the device in terms of sensitivity, thermal noise rejection, and dynamic response. Upon investigation of possible noise sources, a thermally induced sensor drift was found to be the most significant factor affecting the sensors response. A static temperature compensation reduced this drift to less than 120 mL per 12-hr period. Further improvements to the design of the ferromagnetic transducers resulted in a 4.5-fold increase in sensitivity over the previous designs. Results from dynamic testing of the sensor revealed a time constant of 0.4 seconds, which was found adequate for the envisioned application.

Micro-Electro-Mechanical devices have shown enormous popularity in engineering devices as sensors and actuators. In this paper, the instability, i.e. the dynamic pull-in behavior, of an electrically actuated circular micro-membrane is studied. In order to investigate the periodic solutions, detect bifurcations and follow branches of the solution, the non-linear equation of motion is derived using an energy approach, and, is solved by using a pseudo arc-length continuation and collocation technique. It has been shown that, both hardening and/or softening nonlinear responses could emerge depending on the applied DC voltage. The results indicate that the critical load parameters, namely DC and AC voltages and the excitation frequency, have a major influence on the pull-in characteristics of the micro-membrane. The results reveal different dynamic pull-in mechanisms. In addition, they accurately show the decrease of the pull-in voltage due to dynamic loading. The proposed approximate solution is very fast and robust for detecting the pull-in instability. It allows observation of both global and local softening behavior even close to dynamic pullin, where the resonance frequency is almost equal to zero.

Gas turbine engines often pass through tests in enclosed test facilities. One problem that arises during these tests is the infrasound phenomenon. Infrasound can be a problem for many reasons, ranging from rattling windows to structural damage to the test cell. The aim of this paper is to understand the cause of severe infrasound experienced at Honeywell Aerospace and to evaluate and select a solution using advanced Computational Fluid Dynamics (CFD) techniques. These CFD simulations modeled an entire test cell with an engine in place, which is a more complete approach than what is reported in the literature. The DES turbulence model was applied in a transient, compressible, turbulent simulation in order to capture small pressure fluctuations. Test data taken using an engine/test cell configuration that does not cause problems was used to successfully validate the CFD approach. It was found that the narrow, high-velocity exhaust plume examined in this study impacted the convex blast plate in the aft portion of the test cell having diffused only slightly. The exhaust then rebounded and buffeted the plume, causing extreme dynamic loading. Through a modification to the blast basket, it was shown that the problem would be alleviated and sound pressure levels in the test cell would be reduced by 5 to 32 dB, depending on location in the test cell.

This paper examines the implementation of Nitinol wire as a complex-shape actuation source specifically targeted for low-power muscle biomimetics. Nitinol is a type of shape memory alloy (SMA) which recovers its original shape after experiencing large deformation when heated above an austenite finish temperature. Previous preliminary work by the authors demonstrated successful closed-loop force control (i.e., recovery stress) using a simple proportional controller. The work presented in this paper builds upon the previous work by demonstrating closed-loop position control of various wire arrangements in the presence of inertial loads. A predeformed NiTi (4% pre-strain) wire is energized via Joule heating (martensite to austenite) and de-energized by conductive cooling (austenite to martensite). The experimental setup consists of a horizontally arranged NiTi wire (or wire bundle) fixed at one end and connected to a hanging weight through a pulley on the opposite end. The angular displacement of the pulley is measured with a non-contact magnetostrictive angle sensor, thereby providing the control feedback signal for the wire displacement. Successful closed-loop position control is demonstrated, and the relative ease of control is assessed for increasing weights. Given the dynamic loading of the moving wire, a proportional controller alone is insufficient to obtain stabilized responses. Therefore, PID with anti-windup method is employed. Although PID requires some trial and error and is quite sensitive to varying conditions, it appears to be stable and sufficiently precise when properly tuned. The effect of bundling wires on the speed of response is experimentally characterized, and different bundling arrangements are designed and examined in order to increase the geometric rate of convective heat transfer. Increasing the rate of heat transfer is particularly important during the forward (austenite-to-martensite) transformation, since its speed relies solely on passive cooling of the wires. Limitations in controlled load capabilities are discussed in the context of wire diameter, bundle size and controller tuning. A repeatability study of a properly tuned PID controller is also carried out by comparing the first few and last few samples of a 50,000-cycle test. In addition, it is shown that identical wires, when swapped, do not require re-tuning of the PID gains. Finally, this paper shows some preliminary actuator designs that can mimic complex muscle movement. Various geometric arrangements of Nitinol wires are embedded into a curable elastomer with skin-like flexibility and durometer. The potential facial muscle movements from these arrangements are shown and discussed.

Mechanical ventilation is the process of providing artificial breathing support to a patient. More than half of critically ill patients require mechanical ventilation[1]. Though mechanical ventilation increases time for recuperation, it is known to have given rise to complications arising from over-distention of lungs leading to ventilator associated lung injury (VALI) and ventilator induced lung injury (VILI). This paper aims to develop a sensor to identify breathing efforts initiated by the patient and give back responses to the ventilator to regulate ventilation modes and tidal volumes delivered by the ventilator. This will significantly aid in reducing asynchrony between the patient efforts and the ventilator input, thus preventing lung injury. Towards this end, we have simulated and studied the effect of different kinds of dynamic loading and diaphragm membrane thickness of the sensor on its sensitivity on a basic design.

Due to its extensive application, the safety issue of lithium-ion battery has received increasing attention. For crashworthiness design of battery in electric vehicles, it is of great importance to investigate the response of the battery under mechanical loading and understand the mechanism of internal short circuit. Quasi-static and intermediate strain rate uniaxial tension tests were conducted on the electrodes and the separators. The high speed camera and DIC (digital image correlation) method were adopted to measure the strain while a self-design load cell was used to measure force in dynamic test. Either loading velocity or loading direction was varied in different tests. The upper limit of the test strain rate achieved 66 /sec. All the component materials showed strain rate dependency and separators demonstrated noticeable anisotropy. Quasi-static penetration tests were conducted on two different types of pouch cell using steel and plastic punch heads. For both Type A pouch cell and Type B pouch cell, during penetration process using plastic punch head, no significant voltage drop or temperature rise was observed. During penetration process using steel punch head, only Type A pouch cell produced short circuit. When the punch head was removed, the voltage of the cells could recover to certain level. From post mortem examination, it was found that for a single pouch cell, all the electrodes presented the same fracture mode that the stacked anode and cathode formed several fragments in the penetration path, while the separators in between only formed a central crack when the punch head went through. Since the separators had a larger elongation ratio than the electrodes, the extended separators around the rupture location could block the direct and constant contact between anode and cathode, electrodes and steel punch, which explained why no massive internal short circuit was initiated. The drop tower was used to conduct dynamic penetration test. The results indicated that under dynamic loading, internal short circuit was more likely to be triggered which can be explained by the strain rate effect of the separators. This study highlighted the importance of the separator to the safety performance of pouch cells.

Sheet metals usually exhibit a certain degree of plastic anisotropy because of the rolling effect. To characterize the anisotropic behavior in simulations related to large deformation, strain-rate independent phenomenological models are frequently used in quasi-static conditions. Two functions are generally included in such a model, i.e. the yield function and the plastic potential. The former limits the stress state within the yield surface while the latter determines the direction of the plastic strain increment. Traditional plasticity models mostly assume associated flow rule, in which the two functions mentioned above are identical. With the enhanced demand of accuracy, the forms of the associated models become too complex with more and more parameters to achieve an easy calibration procedure. Alternatively, in the past decade the non-associated models were increasingly used for sheet metals. Separate functions for the two aspects of plasticity lead to efficient characterization and convenient calibration. In numerical study of dynamic loading cases, how to characterize strain-rate dependence of plasticity is an important issue. Some visco-plastic models were developed to take the rate effect into account, e.g. Johnson-Cook and Cowper-Symonds models, where the isotropic J2 flow theory was commonly used. However, when the material is severely anisotropic, this approach is very likely to be insufficient, and a model including both anisotropy and rate dependence would be needed. Extending a non-associated anisotropic model to be rate-dependent is a promising approach which has not been published in open literature to the best knowledge of the authors. Objective of the present study is to develop an applicable model for characterizing dynamic mechanical behavior of a typical high-strength steel sheet. Two steps are performed. The material is investigated under quasi-static loading firstly. Tensile test results show an obvious anisotropy which cannot be described by traditional associated models. So the non-associated Hill48 model is chosen and calibrated. Accuracy of the model is verified by a quasi-static punching test. Thereafter the dynamic material properties are obtained by conducting tensile tests at quite a few strain-rate levels covering 0.0004–1200s −1 . To characterize the positive strain-rate effect in strength, the non-associated Hill48 model is extended to be visco-plastic after checking two rate-dependence formulations in existing isotropic models. With implementing the extended model into a user subroutine of ABAQUS/explicit, simulations of the dynamic tension tests are run and compared to the real experiments. A good agreement between the simulated and the experimental result is achieved using the VUMAT.

In this paper a nonlinear human knee dynamics model to include viscoelastic ligaments is proposed. The knee model is two dimensional and include tibia, femur, ligamentous knee structure, and knee cartilages. The model is used to investigate the influence of ligamentous viscoelastic properties on dynamic testing of human knee. An exercise in which the femur is pinned at the hip in a sitting position, and tibia in a vertical position is actuated by a vertical harmonic force at various frequencies is proposed. The viscoelastic model of ligaments shows better predictions on the knee dynamic testing.

Passive vibration isolators are extensively used in wide ranging applications such as automotive, aerospace, railroad and earth moving equipment in the mechanical industry, and in structural applications in the civil industry. These isolators serve as spring-damper units that isolate specific parts of a system from external dynamic loading, or from other sub-systems that cause vibration excitation. Passive isolators exhibit very complex behavior that depends on excitation frequency, displacement amplitude, ambient temperature and pre-load in addition to geometry, design features as well as material composition of the isolator. Various models are prevalent in the existing literature for the design and analysis of such isolators, ranging from the basic Voigt model to more complex models such as the Maxwell-Voigt model with multiple Maxwell elements, the Maxwell ladder model, the three dimensional viscoelastic model, the fractional derivative model, and models specifically used for capturing the hysteresis behavior or the displacement limiting behavior. However, each of these models is successful in representing certain characteristics of the isolator while being unable to capture other key attributes. This paper provides a comparative study of some of the main models that are commonly used for the design and analysis of passive vibration isolators. Experimental data collected from a passive elastomeric isolator under varying excitation conditions is used to identify parameters associated with some of the commonly used models. The analysis results are compared and specific highlights and shortcomings of each model are identified and discussed.

Prior research has shown that the design of a vehicle’s structure has a substantial impact on its overall performance under static loading [1], since the structure affects other components of the vehicle aside from the body. In addition to the past research, dynamic loading is added in this paper as a parameter for design. Bending stiffness and weight are still important factors to consider, since a stiffer structure (higher stiffness) means longer life and stability. A lighter vehicle translates to better fuel economy, lower cost and higher performance. Simple Structural Beams are used to model the structure, where several beam elements are used in the setup. The cross-section properties are analyzed to determine the structure’s weight, bending stiffness, natural frequency and amplitude of vibration. In order to find an acceptable solution, the design must avoid the possibility of resonance. Vibration has a large impact on a structure’s performance, the larger the amplitude, the more uncomfortable the ride is. The goal of this research is to obtain a design that will optimize for vibration and for bending stiffness and weight. The purpose of the optimized design is to provide the best performance and most comfortable ride to the driver. The optimization process is automated iteratively and solves for the beam dimensions that correspond to the optimized parameters.

The optimal performance of a micro-power piezoelectric generator for power harvesting from ambient vibrations strongly depends on the appropriate coupling among its components such as the piezoelectric element, the electrical circuit interface and the load. This coupling is governed by the different types of physical interaction phenomena occurring between such subsystems. A piezoelectric micro-power generator typically consists of a layer of active material deposited on a substrate that convert the mechanical energy from ambient vibrations into electrical energy, an interfacing circuit that usually rectifies this electrical energy and the electrical load where the harvested energy can be stored for later use or spent directly in an application. So far the research efforts in the literature have focused on the performance optimization of each of these subsystems independently, in many cases in an analytical form. Unfortunately, this approach implies a simplification of the models, ruling out most of the complex effects embedded in the dynamic behavior of the system, which does not guarantee optimal performance for the whole device once all its parts are put together. Performance is reduced in the whole device due to different effects such as dynamic loading and impedance mismatch, among others. In order to study the interaction between the subsystems of a micro-power generator, this research proposes a methodology that, by implementing the model for all components on a common a platform, allows for simultaneous analysis and design. A case study is presented and the results demonstrate the potential of the technique for cross-layer optimization of micro-power generators in connection with their associated electronics circuitry.

Injury prediction and mitigation are common overarching goals of modern biomechanical research. This research is fundamental to preventing and mitigating injuries sustained by those exposed to dangerous conditions including but not limited to occupational hazards, warfighter risks, automotive accidents, etc. Unlike traditional mechanical system research, biological systems are difficult and costly to test resulting in a need for robust and accurate numerical simulations. Models of the cervical spine are complex, nonlinear systems that must accurately model dynamic loading, large deflections, elastic, and viscoelastic behavior. In addition to individual complexities, population variance in both material properties and shape must be taken into account for accurate injury prediction. As part of a hierarchical validation and verification (V&V) methodology, lateral impact cadaveric cervical spine experiments were compared to a high fidelity statistical shape finite element model (SSFEM) of the cervical spine and head. Specimens were mounted to a sled and accelerated using a pendulum impact with 1, 2, and 3 m/s impact velocities. The kinematics of the head and all individual cervical vertebrae were recorded with a Vicon motion capture system along with sled acceleration data. Sled accelerations were used as input boundary conditions for the probabilistic study using the SSFEM. Head and vertebrae rotations between the experimental and model responses were then compared. A latin hypercube probabilistic analysis was performed for each impact velocity to determine the probabilistic response of each rotation metric. When comparing these responses, both the average and variation must be taken into consideration. This is accomplished using a quantitative validation metric based on the area between the cumulative distribution functions (CDF) of experimental response and the computed probabilistic response. Our results showed a very good match between the model and experiment at the higher impact velocities and a slightly stiffer response at lower rates. These results are consistent with previous validation studies performed with this SSFEM. By expanding the validation data set with lateral impact loading, greater confidence in the model is obtained under different loading modes. This confidence allows the model to be used for probability of injury predictions as well as to identify important system variables in preventing injuries. High fidelity numeric modeling allows for rapid and cost effective assessment of hazardous loading conditions and safety equipment compared to experimental modeling. The knowledge gained from these modeling studies is fundamental and necessary for safe and effective design and injury mitigation.

Three energy absorption mechanisms of severe dynamic loading events are numerically investigated using a finite element model of a cross-ply unidirectional (UD) composite laminate. In this study, the inelastic energy absorption mechanisms associated with damage at the interfacial and constituent levels were numerically characterized through three admissible failure modes: fiber breakage, matrix shearing, and fiber/matrix debonding (delamination) (i.e., cohesive failure). The UD composite was constructed of ultrahigh molecular weight polyethylene (UHMWPE) fibers separately reinforced with a rigid (epoxy) matrix material. The energy absorption capacities of these damage mechanisms were contrasted for three different dynamic loading cases including blast, shock, and ballistic impact at three different energy levels. Energy loss due to cohesive failure was observed in all three loading cases and energy levels. Furthermore, energy loss due to matrix failure was observed at all energy levels for the blast case, but only for the highest energy level in the shock and ballistics. There was energy loss due to fiber failure in the blast and in the highest energy ballistics impact case. However, there wasn’t any fiber damage in the shock case.

Tendons and ligaments are complex multi-scale collageneous structures playing a fundamental role in mouvement. Even if these tissues are extensively studied in the past decades, modeling their non-linear viscoelastic properties is still a tough challenge. In order to reveal the relationship between the multi-scale structures and the macroscopic mechanical properties, we used atomic force microscopy (AFM) and second harmonic generation (SHG) microscopy to study unstreateched microtome slices of rabbit Achilles tendons, and an Adamel Lomargy DY.22 tensile test machine to study the dynamic properties of these tissues. Based on our data, a Zener model was used to describe the dynamic loading and unloading cycles.