A validated finite element study of blunt trauma to the human maxilla

Six embalmed cadaver heads were obtained, prepared and subsequently impacted to the medial maxilla with a 142-gram baseball traveling at 14 m/s. Measurements of strain were obtained through the use of strain gauge rosettes located at the medial palate and both canine fossae. Three dimensional finite element models of a dentate human maxilla were constructed for the purpose of investigating the mechanical response to a simulated blunt impact. Convergence testing revealed that a refined mesh with over 70,000 degrees of freedom was necessary to obtain sufficient accuracy within the analysis. The simulated load case involved a transient, dynamic impact to the medial maxilla with boundary conditions imposed at the buccal segments of the model analogous to the experimental case. Results were validated by a direct comparison to the displacements and principal strains gathered from experimental and epidemiological data. For the examined load case, displacements were highly localized at the anterior portion of the maxillary incisors. The comparison of experimental and calculated principal strains as a result of the simulated impacts revealed a 1.67 to 11.37% difference in magnitude.

A validated finite element study of blunt trauma to the human maxilla

Six embalmed cadaver heads were obtained, prepared and subsequently impacted to the medial maxilla with a 142-gram baseball traveling at 14 m/s. Measurements of strain were obtained through the use of strain gauge rosettes located at the medial palate and both canine fossae. Three dimensional finite element models of a dentate human maxilla were constructed for the purpose of investigating the mechanical response to a simulated blunt impact. Convergence testing revealed that a refined mesh with over 70,000 degrees of freedom was necessary to obtain sufficient accuracy within the analysis. The simulated load case involved a transient, dynamic impact to the medial maxilla with boundary conditions imposed at the buccal segments of the model analogous to the experimental case. Results were validated by a direct comparison to the displacements and principal strains gathered from experimental and epidemiological data. For the examined load case, displacements were highly localized at the anterior portion of the maxillary incisors. The comparison of experimental and calculated principal strains as a result of the simulated impacts revealed a 1.67 to 11.37% difference in magnitude.

Electrohydraulic Forming of Low Volume and Prototype Parts: Process Design and Practical Examples

Electro-Hydraulic Forming (EHF) is a high rate sheet metal forming process based on the electrical discharge of high voltage capacitors in a water-filled chamber. During the discharge, the pulsed pressure wave propagates from the electrodes and forms a sheet metal blank into a die. The performed literature review shows that this technology is suitable for forming parts of a broad range of dimensions and complex shapes. One of the barriers for broader implementation of this technology is the complexity of a full-scale simulation of EHF which includes the simulation of an expanding plasma channel, the propagation of waves in a fluid filled chamber, and the high-rate forming of a blank in contact with a rigid die. The objective of the presented paper is to establish methods of designing the EHF processes using simplified methods. The paper describes a numerical approach on how to define the shape of preforming pockets. The concept includes imposing principal strains from the formed blank into the initial mesh of the flat blank. The principal strains are applied with the opposite sign creating compression in the flat blank. The corresponding principal stresses in the blank are calculated based upon Hooke’s law. The blank is then virtually placed between two rigid plates. One of the plates has windows into which the material is getting bulged driven by the in-plane compressive stresses. The prediction of the shape of the bulged sheet provides the information on the shape of the preforming pockets. It is experimentally demonstrated that using these approaches, EHF forming is feasible for forming of a fragment of a decklid panel and a deep panel with complex curvature.

Strain relaxation in InGaN/GaN epilayers by formation of V-pit defects studied by SEM, XRD and numerical simulations

V-pit defects in InGaN/GaN were studied by numerical simulations of the strain field and X-ray diffraction (XRD) reciprocal space maps. The results were compared with XRD and scanning electron microscopy (SEM) experimental data collected from a series of samples grown by metal–organic vapor phase epitaxy. Analysis of the principal strains and their directions in the vicinity of V-pits explains the pseudomorphic position of the InGaN epilayer peak observed by X-ray diffraction reciprocal space mapping. The top part of the InGaN layer involving V-pits relieves the strain by elastic relaxation. Plastic relaxation by misfit dislocations is not observed. The creation of the V-pits appears to be a sufficient mechanism for strain relaxation in InGaN/GaN epilayers.

Optimization of the geometry of specimens with transversal groove for materials with initial anisotropy

The goal of the study is determination of the optimal geometric dimensions of rectangular anisotropic specimens with a transverse groove when tested for uniaxial tension under conditions close to plane deformation. A test scheme in which the shear fracture mechanism is implemented in the center of the groove under conditions of plane deformation is presented. The optimal geometric dimensions of the specimen (namely, the depth, width and length of the transversal groove) were determined proceeding from numerical simulation of the experiment in the ABAQUS software package in the Explicit mode. It is shown that the initial anisotropy of the material significantly affects the deformed state in the groove. The larger the ratio of the Lankford coefficients along the rolling direction and across this direction, the closer the deformed state in the groove to the plane deformation. It is also shown that change in the geometry of the specimen with a transverse groove can provide better results in implementation of the plane deformation in the region of specimen fracture. The value of the parameter of the deformed state approaches zero when the thickness and width of the groove decrease, as well as when the width of the specimen increases. It is shown that the possibility of forming plane deformation in the groove due to the choice of specimen geometry is limited from above for any initial anisotropy. A moment of «saturation» is observed, at which the ratio of principal strains in the center of the groove does not go any further to zero despite further change in the geometry. A table of geometric dimensions of rectangular specimens with a transverse groove recommended for tensile testing under conditions of plane deformation for all types of anisotropic and isotropic sheet materials is presented.

Selected Concrete Models Studied Using Willam’s Test

Willam’s test is a quick numerical benchmark in tension–shear regime, which can be used to verify inelastic (quasi-brittle) material models at the point level. Its sequence consists of two separate steps: uniaxial tension accompanied with contraction—until the tensile strength is attained; and next for softening (cracking) of the material—tension in two directions together with shear. A rotation of axes of principal strains and principal stresses is provoked in the second stage. That kind of process occurs during the analysis of real concrete structures, so a correct response of the material model at the point level is needed. Some familiar concrete models are selected to perform Willam’s test in the paper: concrete damaged plasticity and concrete smeared cracking—distributed in the commercial ABAQUS software, scalar damage with coupling to plasticity and isotropic damage—both implemented in the FEAP package. After a brief review of the theory, computations for each model are discussed. Passing or failing Willam’s test by the above models is concluded based on their results, indicating restrictions of their use for finite element computations of concrete structures with predominant mixed-mode fracture.

Development of limb bone laminarity in the homing pigeon (Columba livia)

Background Birds show adaptations in limb bone shape that are associated with resisting locomotor loads. Whether comparable adaptations occur in the microstructure of avian cortical bone is less clear. One proposed microstructural adaptation is laminar bone in which the proportion of circumferentially-oriented vascular canals (i.e., laminarity) is large. Previous work on adult birds shows elevated laminarity in specific limb elements of some taxa, presumably to resist torsion-induced shear strain during locomotion. However, more recent analyses using improved measurements in adult birds and bats reveal lower laminarity than expected in bones associated with torsional loading. Even so, there may still be support for the resistance hypothesis if laminarity increases with growth and locomotor maturation. Methods Here, we tested that hypothesis using a growth series of 17 homing pigeons (15–563 g). Torsional rigidity and laminarity of limb bones were measured from histological sections sampled from midshaft. Ontogenetic trends in laminarity were assessed using principal component analysis to reduce dimensionality followed by beta regression with a logit link function. Results We found that torsional rigidity of limb bones increases disproportionately with growth, consistent with rapid structural compensation associated with locomotor maturation. However, laminarity decreases with maturity, weakening the hypothesis that high laminarity is a flight adaptation at least in the pigeon. Instead, the histological results suggest that low laminarity, specifically the relative proportion of longitudinal canals aligned with peak principal strains, may better reflect the loading history of a bone.

A Principal Strain Data-Driven Method for Damage Identification of an Offshore Pile Structure

Vibration-based damage identification technique, categorized as parametric and nonparametric methods, plays an important role in guaranteeing the success of offshore operations and the integrity management of marine structures. In the parametric approaches, modal parameters and their derivative are usually applied to obtain the damage-sensitive features. Nevertheless, there are still some challenging problems for the parametric method in application. Nonparametric (data-driven) approaches are aim to extract damage sensitive features directly from the measured data. For the data-driven approaches, it is vital to find which indicator derived from the response signal is sensitive to structural damage. Considering the derivatives of strain are more sensitive to small structural damage than that of displacement, the strain-related damage detection methods have currently gotten more attention. In this study, a principal strain data-driven method is proposed, which is derived from strain energy dispersion theory and directly employs the time history data of three principal strains of an intact and damaged structure to construct the damage identification indicator. The efficiency of the method is validated by a numerical offshore pile structure with several damage cases considering noise scenarios. Due to the difficulty of determine the correct three principal strains in the real experimental measurements, the approximation damage indicators are constructed based on one, two or three kinds of strain response among the axial, radial and hoop strains response, instead of the three principal strains response. The results show that satisfying damage identification results can still be gotten for both the single- and multiple-damage scenarios using only axial or hoop strain response even under noise conditions. The proposed principal strain data-driven damage identification method can be used as a viable and effective technique for damage localization and severity estimation of marine structures.

Facing Up to Scarcity

The essays collected in this book take stock of the nonconsequentialist project over the past fifty years, in two key areas. The first part focuses on the moral “duty not to harm” others. Under a suitably broad definition of harm, that duty encompasses most of the restrictions imposed on individual conduct in the secular, liberal state. It examines how that duty has been cashed out in ostensibly nonaggregative terms in the principal strains of nonconsequentialist thought: tragic choices (trolleyology), libertarian property rights, corrective justice in tort law, and Scanlonian contractualism. Nonconsequentialists have not only failed to articulate a viable alternative to aggregation in this domain; they are doomed to fail, because in a world of scarcity (in the broadest sense) and epistemic uncertainty, everything we do poses some risk of harm to others’ fundamental interests, a conflict that can be resolved only through aggregation. The second part examines the treatment of distributive justice in nonconsequentialist political theory over the past fifty years, focusing on Nozickian libertarianism, Rawlsianism, left-libertarianism, and social contractarianism. It argues that whatever the moral attractiveness of the various distributive schemes proposed, none is logically entailed by the normative premises from which it is ostensibly derived. Unlike the argument in the first part, this is not an argument for consequentialism by logical elimination. Societal wealth need not be, and almost never is, distributed to optimize consequences. Rather, it underscores the relatively weak justifications that have been offered for some very strong conclusions.