Determination of material constants and hydraulic strengthening of trabecular bone through an orthotropic structural model

Biorheology ◽  
1994 ◽  
Vol 31 (3) ◽  
pp. 245-257 ◽  
Author(s):  
D.D. Deligianni ◽  
Y.F. Missirlis ◽  
V. Kafka
Keyword(s):  
Trabecular Bone ◽  
Structural Model ◽  
Material Constants

Influence of Human Error on Structural Reliability

2017 ◽  
Author(s):  
Eric Brehm ◽  
Robert Hertle ◽  
Markus Wetzel
Keyword(s):  
Human Error ◽  
Structural Reliability ◽  
Failure Modes ◽  
Structural Model ◽  
Limit State ◽  
Design Procedure ◽  
Material Strength ◽  
Limit States ◽  
The Impact

In common structural design, random variables, such as material strength or loads, are represented by fixed numbers defined in design codes. This is also referred to as deterministic design. Addressing the random character of these variables directly, the probabilistic design procedure allows the determination of the probability of exceeding a defined limit state. This probability is referred to as failure probability. From there, the structural reliability, representing the survival probability, can be determined. Structural reliability thus is a property of a structure or structural member, depending on the relevant limit states, failure modes and basic variables. This is the basis for the determination of partial safety factors which are, for sake of a simpler design, applied within deterministic design procedures. In addition to the basic variables in terms of material and loads, further basic variables representing the structural model have to be considered. These depend strongly on the experience of the design engineer and the level of detailing of the model. However, in the clear majority of cases [1] failure does not occur due to unexpectedly high or low values of loads or material strength. The most common reasons for failure are human errors in design and execution. This paper will provide practical examples of original designs affected by human error and will assess the impact on structural reliability.

Structure determination of the stable anhydrous phase of α-lactose from X-ray powder diffraction

2005 ◽  
Vol 61 (2) ◽  
pp. 185-191 ◽  
Author(s):  
Cyril Platteau ◽  
Jacques Lefebvre ◽  
Frederic Affouard ◽  
Jean-François Willart ◽  
Patrick Derollez ◽  
...  
Keyword(s):  
Powder Diffraction ◽  
Room Temperature ◽  
Structural Model ◽  
Hydroxyl Groups ◽  
Rietveld Refinements ◽  
X Ray ◽  
Hydrogen Bond Networks ◽  
Monte Carlo Simulated Annealing ◽  
Annealing Method

The stable anhydrous form of α-lactose has been obtained by the dehydration of α-lactose monohydrate in methanol. An X-ray powder diffraction pattern was recorded at room temperature with a laboratory diffractometer equipped with an INEL curved sensitive detector CPS120. The starting structural model of this form was found by a Monte-Carlo simulated annealing method. The structure was obtained through Rietveld refinements and the minimization of crystalline energy for the localization of the H atoms of the hydroxyl groups. Soft restraints were applied to bond lengths and angles. Networks of O—H...O hydrogen bonds account for the crystalline cohesion. A comparison is made between the hydrogen-bond networks of this form and those of the monohydrate and hygroscopic anhydrous forms of α-lactose.

On Differences of Statically and Dynamically Determined Elastic Modules of Materials Like Trabecular Bone

2007 ◽  
Author(s):  
D. H. Besdo ◽  
S. Besdo
Keyword(s):  
Trabecular Bone ◽  
Cross Sections ◽  
Step Function ◽  
Shear Mode ◽  
Variable Cross ◽  
Half Cycle ◽  
Longitudinal Waves ◽  
Ultrasonic Methods ◽  
Elastic Modules

The linear elastic material law which is usually applied in simulations of bone behavior reads σij = Cijkl εkl. It contains up to 21 independent constants. In most applications only nine constants (orthotropic behavior) are used. The determination of these constants is troublesome. The most applied experimental method is based on ultrasonic wave propagation. As it is often recognized the elastic modules measured by this method differ significantly from those found by static testing. Whereas Young’s modules differ slightly only, the determination of shear modules by ultrasonic methods is extremely doubtful, especially in trabecular bone. To find reasons for this effect, wave propagations are simulated by Finite-Element-techniques. This is done for artificial structures and also for realistic models of trabecular bone based one μCT-data. It can be recognized that in structured media always three types of waves propagate through the material with different speeds. Unfortunately the shear wave which is to be measured is the slowest one. Even if no longitudinal waves disturb the measurements, at least bending waves appear and pretend some kind of shear mode. The different orientations of the trabeculae can cause longitudinal waves when shear waves are applied. The stimulation of the ultrasound is at first simulated as a half cycle or as a step function only. The realistic waves are superimpositions of several of such motions. Such a relatively simple simulation makes possible to distinguish the three wave types mentioned above. The superimpositions complicate the motion extremely. Also reflection, damping and variable cross sections make it almost impossible to identify the modules, especially the shear modules, in a certain manner.

Direct Prediction of the Effects of Mistuning on the Forced Response of Bladed Disks

1998 ◽  
Vol 120 (3) ◽  
pp. 626-634 ◽  
Author(s):  
M. P. Mignolet ◽  
W. Hu
Keyword(s):  
Structural Model ◽  
Order Approximation ◽  
Forced Response ◽  
Blade Vibration ◽  
First Order ◽  
Bladed Disk ◽  
Novel Approach ◽  
Error Terms ◽  
First Order Approximation

In this paper, a novel approach to determine reliable estimates of the moments of the steady-state resonant response of a randomly mistuned bladed disk is presented, and the use of these moments to accurately predict the corresponding distribution of the amplitude of blade vibration is described. The estimation of the moments of the response is accomplished first by relying on a “joint cumulant closure” strategy that expresses higher order moments in terms of lower order ones. A simple modeling of the error terms of these approximations is also suggested that allows the determination of an improved, or accelerated, estimate of the required moments. The evaluation of the distribution of the amplitude of blade response is then accomplished by matching the moments computed by the cumulant closure with those derived from a three-parameter model recently derived. A first order approximation of the moments obtained for a simple structural model of a bladed disk yields a new parameter that can be used as a measure of the localization of the forced response. Then, numerical results demonstrate that the method provides extremely accurate estimates of the moments for all levels of structural coupling which in turn lead to a description of the amplitude of blade response that closely matches simulation results. Finally, a comparison with existing perturbation techniques clearly shows the increased accuracy obtained with the proposed joint cumulant closure formulation.

An improved structural model for cellulose II

2013 ◽  
Vol 28 (3) ◽  
pp. 194-199 ◽  
Author(s):  
James A. Kaduk ◽  
Thomas N. Blanton
Keyword(s):  
Density Functional ◽  
Structural Model ◽  
Rietveld Method ◽  
Geometry Optimization ◽  
Precise Determination ◽  
Unit Cell ◽  
Cellulose Ii ◽  
Unit Cell Parameters ◽  
Cell Parameters

A sample of cellulose II, prepared by deacetylation of cellulose acetate, has permitted more precise determination of the unit-cell parameters by the Rietveld method. Cellulose II is monoclinic, with space group P21c-axis unique (or P1121) (No. 4) and refined unit-cell parameters a = 8.076(13), b = 9.144(10), c = 10.386(20) Å, γ = 117.00(8)°, and V = 683.5(18) Å3. A density functional geometry optimization using these fixed unit-cell parameters has resulted in an improved structural model for cellulose II. A powder pattern calculated from this new model has been submitted to the ICDD for inclusion in future releases of the Powder Diffraction File.

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