Different Directions Of Loading Research Articles

P8. Correlations between sagittal plane disc dimensions and principal surface strains across the L3-4 intact IVD during in vitro multidirectional loading

<h3>BACKGROUND CONTEXT</h3> Understanding the biomechanical behavior of the intact intervertebral disc (IVD) is of great importance when studying disc disease. Experimental data describing the relationship between disc size and sub-regional principal strains of the intact lumbar intervertebral disc during multi-directional loading are lacking. <h3>PURPOSE</h3> The purpose of this study was to investigate possible relationships between lateral view disc dimensions and principal surface strains across different regions of an intact L3-4 disc assessed using digital image correlation (DIC) during multi-directional loading. <h3>STUDY DESIGN/SETTING</h3> Correlation analysis of dimensional data obtained from lateral X-rays of intact L3-4 lumbar discs at rest and principal surface strains of the same discs obtained from digital image correlation analysis during in vitro loading. <h3>PATIENT SAMPLE</h3> There were 14 cadaveric spine segments including 6F/8M, mean(±SD) age: 45±13years; BMD: 0.916±0.120 g/cm2. <h3>OUTCOME MEASURES</h3> Correlation coefficients (and p-values) between disc dimensions (sagittal view disc height and area) and principal surface strains during multi-directional loading, in sub-regions of intact L3-4 IVD. <h3>METHODS</h3> The mean height and depth of the L3-4 IVD of 14 seemingly healthy human spine segments at rest were determined using lateral view X-rays and ImageJ. The IVDs were part of L3-S1 spine segments that were tested using non-destructive loading (7.5 Nm) in flexion (FL), extension (EX), right lateral bending (RLB) right/left axial rotation (RAR/LAR), followed by compression (Comp, 400 N). Mean principal strains (Pmax and Pmin) in four similarly sized quarters of the L3-4 IVD were assessed using 3D DIC (Vic-3D) during loading with cameras positioned directly lateral on the specimen's left side. Relationships between sagittal view disc dimensions at rest and mean principal strains per lateral view disc quarter [Q1(ant)-Q4(post)] during loading were studied using Pearson Correlation analysis (SigmaPlot v14 with p<0.05). <h3>RESULTS</h3> Disc height correlated significantly and positively with Pmax (tensile/stretching strain) mid-anteriorly (Q2) during Comp (R=0.545, p=0.044). There were no other significant correlations between disc height and principal strains in any other region of the disc during any direction of loading (p>0.05). In the mid-posterior disc region (Q3), Pmax correlated significantly and negatively with sagittal plane disc area during FL (R=-0.538, p=0.047) and RLB (R=-0.592, p=0.033, Fig.), showing that a larger disc (taller and deeper) bulges/stretches less during flexion and right lateral bending than a smaller disc (narrow disc height combined with shorter vertebral depth, anterior-posteriorly), mid-posteriorly. Pmin (compressive strain) correlated significantly and positively with sagittal plane disc area in the mid-posterior disc region during Comp (Q3: R=0.650, p=0.012; and Q4: R=0.619, p=0.018), indicating that a larger disc (taller and deeper) shrinks less vertically than a small disc posteriorly during compression. <h3>CONCLUSIONS</h3> Significant relationships were found between disc dimensions and mean principal strains in sagittal view sub-regions of the L3-4 intervertebral disc, during different directions of loading. These relationships aid in understanding intact disc biomechanical behavior during loading and will help improve the quality of finite element models of lumbar spine segments. <h3>FDA DEVICE/DRUG STATUS</h3> This abstract does not discuss or include any applicable devices or drugs.

A new method for assessing anisotropy in fused deposition modeled parts using computed tomography data

Voids in fused deposition modeled (FDM) parts are assumed to be a key driver for their anisotropic behavior. However, these assumptions are based on investigations of voids using only 2D data (microscopy images). This paper presents a new method to measure such voids by analyzing 3D-data of from X-ray computed tomography (CT), and application of this data for assessment of mechanical parameters. The article is divided into three parts, where the first part elaborates on a proposed method to assess and characterize the void geometry throughout uniaxial printed FDM parts using CT-data. The second part presents an investigation of the void configurations in samples manufactured using different process parameters, aiming to understand how variation in extrusion rate and compensation for non-linear dynamic extrusion behavior affects the void sizes. The third part displays how the information regarding void sizes could be further related to global mechanical properties, using a multiscale finite element approach. The present method of CT-data analysis gives a clear overview of the spatial variation of the void geometry, and findings from the investigated samples suggest that the size of voids have a large non-random spatial variation, highly dependent on the turning points of the toolpaths, and also significantly affected by accumulation of excess material. Printing at a low extrusion rate increases the void sizes considerably, while implementation of an extrusion dynamics compensation algorithm was found to have low impact on the void sizes. The multiscale finite element approach predicts anisotropic elastic behavior, significantly more compliant in the vertical and transversal direction, relative to the printing direction of the infill. It also predicts a non-isotropic strain energy density throughout the specimen, where the location and magnitude of the most energy dense locations vary significantly for different directions of loading, which implicates an anisotropic behavior in terms of failure, in accordance with literature.

Elastically-isotropic elementary cubic lattices composed of tailored hollow beams

In previous works, mechanical metamaterials exhibiting isotropic elastic properties have been obtained using combinations of the elastically-anisotropic elementary cubic truss lattices (simple-cubic, body-centered cubic or face-centered cubic truss lattice structures). In the present work, a new family of elastically-isotropic elementary cubic truss lattice structures is developed, eliminating the need of combining elementary structures to achieve elastic isotropy. Depending on the direction of loading, the nature of the mechanical response of cubic elementary trusses changes smoothly from bending-dominated to stretching-dominated. It is thus possible to tailor the apparent anisotropy at the macroscopic level by changing the ratio of bending-to-axial stiffness of the constituent beams. Here, the latter is achieved by changing the ratio of inner-to-outer diameter of hollow tubes. It is shown through unit cell simulations that an optimal diameter ratio exists achieving elastic isotropy for all three elementary cubic trusses for the full range of relative densities considered (1 to 50%). Selected polymer trusses are additively-manufactured using stereolithography and subjected to uniaxial compression along different directions of loading to provide a partial experimental validation of the proposed design maps.

Evaluation of Anisotropy of Fracture Toughness in Brittle Rock, Migmatized Gneiss

Most rocks in nature are affected by a certain degree of anisotropy. They contain cracks mostly with certain distributions. Therefore their mechanical behaviour is dependent on the direction of the strength distribution, which is different in each direction. We can distinguish the directions in which the rock is relatively firm and conversely the directions in which it is weak. The strength anisotropy and the direction of weakening is useful information for engineering applications. Metamorphic foliation with the specific orientation of rock grains also influences the mechanical behaviour, and the mechanical properties, i.e. strength, are changed in different directions of loading. This change of strength is called the strength anisotropy. The main purpose of this research is to analyze the effect of the orientation of metamorphic foliation distinguished within the rock specimens on their strength anisotropy. In the article, the anisotropy of a mechanical property, i.e. the fracture toughness, of migmatized gneiss is discussed. For this purpose, series of semi-circular bend tests were carried out on specimens of migmatized gneiss with a metamorphic foliation. The methodology used in this research is effective for evaluating the strength anisotropy of a brittle rock.

Experimental and Numerical Evaluation of the Mechanical Behavior of Strongly Anisotropic Light-Weight Metallic Fiber Structures under Static and Dynamic Compressive Loading.

Rigid metallic fiber structures made from a variety of different metals and alloys have been investigated mainly with regard to their functional properties such as heat transfer, pressure drop, or filtration characteristics. With the recent advent of aluminum and magnesium-based fiber structures, the application of such structures in light-weight crash absorbers has become conceivable. The present paper therefore elucidates the mechanical behavior of rigid sintered fiber structures under quasi-static and dynamic loading. Special attention is paid to the strongly anisotropic properties observed for different directions of loading in relation to the main fiber orientation. Basically, the structures show an orthotropic behavior; however, a finite thickness of the fiber slabs results in moderate deviations from a purely orthotropic behavior. The morphology of the tested specimens is examined by computed tomography, and experimental results for different directions of loading as well as different relative densities are presented. Numerical calculations were carried out using real structural data derived from the computed tomography data. Depending on the direction of loading, the fiber structures show a distinctively different deformation behavior both experimentally and numerically. Based on these results, the prevalent modes of deformation are discussed and a first comparison with an established polymer foam and an assessment of the applicability of aluminum fiber structures in crash protection devices is attempted.

Micromechanical force sensors based on SU-8 resist

This paper presents an innovative approach to develop highly sensitive 3D force sensors. In order to increase the probing sensitivity by using a material with low Young’s Modulus, a novel force sensor design based on SU-8 polymer is realized. Therefore, a low cost fabrication process is developed accompanied by design studies and an estimation of mechanical properties of the deforming elements. This paper will present the fabrication process as well as a distinguishing set of test results, analytical results, and simulations on the characterization of the presented SU-8 force sensor. The novel SU-8 design consists of an SU-8 boss-membrane with integrated piezoresistive elements. The SU-8 membranes are structured using photolithography. The SU-8 micromechanical structures are characterized to determine film stresses, bending stiffness, displacement of the stylus, and breaking points. Included in these tests are measurement of the stress behavior at different process steps and simulation of stress distribution in the membrane at different directions of loading. In addition a comparative analytical investigation of the structures is carried out particularly with regard to the displacement of the stylus.

Effect of Uni-Axial Tensile Deformation on Microstructure and Magnetic Properties of 3.2% Si Grain Oriented Electrical Steel

Cold rolled grain oriented (CRGO) steel was deformed by uni-axial tensile loading in three different directions: Rolling Direction (RD) (110) , Transverse Direction (TD) (110) and 45° to RD (110) . Deformation behavior was found to be different for the different directions of loading. Such differences were biased by the heat flattening coating and could be captured, effectively, through discrete dislocation dynamics simulations. Results from texture and micro-texture studies, mechanical tests and magnetic measurements show a clear relationship between strain hardening exponent (n) and degradation in magnetic properties (watt loss and permeability). These were also related to misorientation developments, relative recovery and deviations from ideal Goss orientation.

Prediction of proximal femur strength using a CT-based nonlinear finite element method: Differences in predicted fracture load and site with changing load and boundary conditions

The annual occurrence of hip fracture due to osteoporosis as of 2002 had reached 120,000 in Japan. The increase has been very rapid. From a biomechanical perspective, hip fractures are thought to be caused in real settings by different directions of loading. Thus, clarification of the loading directions under which the proximal femur is most vulnerable to fracture would be helpful for elucidating fracture mechanics and establishing preventive interventions. The purpose of the current study was to clarify the influence of loading direction on strength and fracture site of the proximal femur using the CT-based nonlinear FE method to determine loading directions under which the proximal femur is most vulnerable to fracture. Contralateral femora were analyzed in 42 women with hip fracture (mean age, 82.4 years), comprising 20 neck fractures and 22 trochanteric fractures. Within 1 week after fracture, quantitative CT of the contralateral femur was performed in each patient and 3-dimensional FE models were created. One stance loading configuration (SC) and four different fall loading configurations (FC) were assigned. Nonlinear FE analysis was performed. Differences in fracture loads depending on differences in loading direction were analyzed and correlations among fracture loads in different loading directions were assessed. Next, fracture sites were also analyzed. Mean predicted fracture load in the SC was 3150 N. Mean fracture loads were 2270 N in FC1, 1060 N in FC2, 980 N in FC3, and 710 N in FC4. The correlation between predicted fracture loads in SC and those in each FC was significant with a correlation coefficient of 0.467–0.631. Predicted fracture sites in the SC appeared at the subcapital region in all patients and were categorized as neck fracture. However, trochanteric fractures occurred in all fall configurations except FC1. In FC1, a significant correlation was seen between real fracture type and predicted type. The current investigation could contribute to the acquisition of useful knowledge allowing the establishment of more efficacious means of preventing hip fractures.

Strain distribution in the proximal human femoral metaphysis

There is significant interest in the stress-strain state in the proximal femoral metaphysis, because of its relevance for hip fractures and prosthetic replacements. The scope of this work was to provide a better understanding of the strain distribution, and of its correlation with the different directions of loading, and with bone quality. A total of 12 pairs of human femurs were instrumented with strain gauges. Six loading configurations were designed to cover the range of directions spanned by the hip joint force. Inter-specimen variability was reduced if paired specimens were considered. The principal strain magnitude varied greatly between loading configurations. This suggests that different loading configurations need to be simulated in vitro. The strain magnitude varied between locations but, on average, was compatible with the strain values measured in vivo. The strain magnitudes and the direction of principal tensile strain in the head and neck were compatible with the spontaneous fractures of the proximal femur reported in some subjects. The principal tensile strain was significantly larger where the cortical bone was thinner; the compressive strain was larger where the cortical bone was thicker. The direction of the principal strain varied significantly between measurement locations but varied little between loading configurations. This suggests that the anatomy and the distribution of anisotropic material properties enable the proximal femur to respond adequately to the changing direction of daily loading.

Micromechanical Material Model of Wooden Veneers for Numerical Simulations of Plywood Progressive Failure

The plywood material is widely used in civil engineering and furniture industry as cheap, strong, and lightweight material. The progressive failure of the plywood is difficult to be modeled and predicted because of the complexity of its structure and the interaction between different modes of orthogonal damages and interlayer failure. The microstructure of the wood determines the failure of the plies. A micromechanical material model of wooden veneers is developed, which is based on a representative volume cell (RVC) taken from the tubular microstructure of the wood and represented as a truss structure with longitudinal, transverse, and diagonal bar finite elements. The damage variables prescribed for each type of the bars determine the progressive degradation of the material stiffness. The 2-D damage material model of wooden veneers is utilized as user-defined material in continuum shell elements of ABAQUS™ finite element code. The parameters of the model are determined to simulate the behavior of single veneers in tension tests in different directions of loading. Together with cohesive elements representing the interface between the plies, the suggested model can be used to simulate and analyze the progressive failure and damage interaction in the plywood. The simulations could give us better understanding of the complex failure of the plywood, the succession of the damage development and reveal the weakest link in the material. The analysis can be used for optimization of the plywood layup.

Three-dimensional measurements of the pressure distribution in artificial joints with a capacitive sensor array

A spherically folded capacitive pressure sensor array is introduced and characterized. By placing the sensor array between the ball and the cavity of artificial joints, the pressure distribution within the joint was recorded with spatial resolution for different size matching between the ball and the cavity, for different directions of loading and for joints with incomplete cavities. The performance of the sensor array is analyzed, possible fields of application as well as its limitations are discussed.

Abnormal involuntary movements in a general population sample of middle-aged men

In previous works, mechanical metamaterials exhibiting isotropic elastic properties have been obtained using combinations of the elastically-anisotropic elementary cubic truss lattices (simple-cubic, body-centered cubic or face-centered cubic truss lattice structures). In the present work, a new family of elastically-isotropic elementary cubic truss lattice structures is developed, eliminating the need of combining elementary structures to achieve elastic isotropy. Depending on the direction of loading, the nature of the mechanical response of cubic elementary trusses changes smoothly from bending-dominated to stretching-dominated. It is thus possible to tailor the apparent anisotropy at the macroscopic level by changing the ratio of bending-to-axial stiffness of the constituent beams. Here, the latter is achieved by changing the ratio of inner-to-outer diameter of hollow tubes. It is shown through unit cell simulations that an optimal diameter ratio exists achieving elastic isotropy for all three elementary cubic trusses for the full range of relative densities considered (1 to 50%). Selected polymer trusses are additively-manufactured using stereolithography and subjected to uniaxial compression along different directions of loading to provide a partial experimental validation of the proposed design maps.

Effect of rapid cooling on the microstructure and mechanical properties of commercial 85 wt.% Al 2O 3

Tiles of structural 85 wt.% Al 2O 3 were subjected to post-fabrication heat treatment. Microstructural investigation indicated that the material contained two interconnected phases: a skeleton of crystalline Al 2O 3 and about 30 vol.% of an Al 2O 3-rich alumino-silicate glass. Rapid cooling of tiles from high temperatures resulted in an increase in transverse rupture strength σ trs and of fracture toughness K Ic for three different directions of loading and crack propagation. A pronounced increase in K Ic was also observed for cracks propagating in the mid-plane of the tile normal to the cooling direction, while macroscopic tensile thermal stresses should lead to a decrease in σ trs and K Ic for this case. X-ray analysis showed that rapid cooling from temperatures above 1300°C resulted in dissolution of the anorthite and cordierite precipitates that were observed in the glassy phase in slowly cooled samples. Annealing of rapidly cooled samples at temperatures up to 1000°C with subsequent slow cooling completely removed the effect of rapid cooling on the mechanical properties, even though no precipitation of anorthite or cordierite was observed. The effect of heat treatment on the volume fraction of the glassy phase, the grain size and the density was also investigated.