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Mechanical Parameters (mechanical + parameter)
Selected AbstractsAPPLICATION OF A COMPRESSION-RELAXATION TEST FOR THE CHARACTERIZATION OF BURLAT SWEET CHERRYJOURNAL OF TEXTURE STUDIES, Issue 1 2001PEDRO L. MARQUINA Mechanical parameters of Burlat sweet cherries (Prunus avium) were studied as a function of ripening during three consecutive years by using a penetration test, a compression test between two plates, and a compression-relaxation test. The latter yields the "apparent secant modulus," i. e. the ratio of the initial maximum compression force over the applied strain. This modulus is one of the most useful mechanical parameters to discriminate between batches because its value is clearly related to the variety and degree of ripeness. Thus, the compression-relaxation test consistently allowed the differentiation of cherries in five degrees of ripeness. [source] Acceptable prior fatigue damage and failure threshold for impact loading of an aluminium alloyFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2001T. Auzanneau In a competitive economic context that aims at gains in safety, some problems of combined fatigue-impact loadings are crucial, particularly in the case of light alloys used in the transport and aeronautical industries. One important challenge is to quantify the fatigue preloading effect on the residual dynamic plasticity of a 2017-A T3 aluminium alloy. From an experimental modal analysis, the change in mechanical properties of prefatigued material under impact loading allows us to define the best mechanical parameter for a limiting threshold between a no-damage state and weakened states due to fatigue predamage. For this situation a hybrid technique has been developed. A numerical model including voids (which represent surface micro-cracks produced by the fatigue preloading) is fitted to the results obtained by the modal analysis of the damaged sample. Hence, an acceptable damage threshold (i.e. a damage critical volume below which the impact toughness is not affected by fatigue preloading) and a failure threshold are established. On the basis of this methodology, it is possible to predict the energy required for the impact failure of prefatigued specimens and therefore to predict a safe or a dangerous mechanical state. [source] Sorption behavior in polymers above Tg: Relations between mechanical properties and swelling in limonenePOLYMER ENGINEERING & SCIENCE, Issue 9 2005J.E. Ritums The sorption behavior of two highly swelling "rubbery" polymers, natural rubber and polyethylene, has been studied. The polymers are in many aspects very different. Yet, when the solute mass uptake, in this case limonene, is plotted as a function of the square root of time, both polymers show similar "sigmoidal"-types of curves. This triggered the research to determine what mechanisms were responsible for the observed similarities and if the degree in sigmoidal behavior and swelling anisotropy could be easily assessed explicitly by any mechanical parameter. It was found that their degrees of swelling anisotropy, described by a solute-surface-concentration relaxation time, could be explained by their relative bulk moduli. It was assumed that the ratio in bulk modulus at zero pressure, determined from compression measurements, could represent the ratio in expansion bulk modulus during swelling. However, the prediction in swelling anisotropy during sorption using the ratio in bulk modulus was slightly less successful when the swelling anisotropy was quantified as the relative ratio of sheet thickness to cross-sectional area side length. It should be noted that the ratio in uniaxial tensile modulus between polyethylene and natural rubber was several orders of magnitude higher than their ratio in swelling anisotropy. The natural rubber sheet became saddle-shaped during limonene sorption and collapsed into a flat shape when the saturation concentration was approached. During desorption, the sheet went from flat to cup-shaped and then flat again at the end of desorption. The saddle and cup shapes occurred in both square and round sheets. These shapes are believed to be a consequence of buckling and deformation due to instabilities in the stress state of the sheet. This was, in turn, explained by the normally existing local variation in cross-link density. POLYM. ENG. SCI., 45:1194,1202, 2005. © 2005 Society of Plastics Engineers [source] Full waveform inversion of seismic waves reflected in a stratified porous mediumGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2010Louis De Barros SUMMARY In reservoir geophysics applications, seismic imaging techniques are expected to provide as much information as possible on fluid-filled reservoir rocks. Since seismograms are, to some degree, sensitive to the mechanical parameters and fluid properties of porous media, inversion methods can be devised to directly estimate these quantities from the waveforms obtained in seismic reflection experiments. An inversion algorithm that uses a generalized least-squares, quasi-Newton approach is described to determine the porosity, permeability, interstitial fluid properties and mechanical parameters of porous media. The proposed algorithm proceeds by iteratively minimizing a misfit function between observed data and synthetic wavefields computed with the Biot theory. Simple models consisting of plane-layered, fluid-saturated and poro-elastic media are considered to demonstrate the concept and evaluate the performance of such a full waveform inversion scheme. Numerical experiments show that, when applied to synthetic data, the inversion procedure can accurately reconstruct the vertical distribution of a single model parameter, if all other parameters are perfectly known. However, the coupling between some of the model parameters does not permit the reconstruction of several model parameters at the same time. To get around this problem, we consider composite parameters defined from the original model properties and from a priori information, such as the fluid saturation rate or the lithology, to reduce the number of unknowns. Another possibility is to apply this inversion algorithm to time-lapse surveys carried out for fluid substitution problems, such as CO2 injection, since in this case only a few parameters may vary as a function of time. We define a two-step differential inversion approach which allows us to reconstruct the fluid saturation rate in reservoir layers, even though the medium properties are poorly known. [source] Coupled HM analysis using zero-thickness interface elements with double nodes,Part II: Verification and applicationINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 18 2008J. M. Segura Abstract In a companion Part I of this paper (Int. J. Numer. Anal. Meth. Geomech. 2008; DOI: 10.1002/nag.735), a coupled hydro-mechanical (HM) formulation for geomaterials with discontinuities based on the finite element method (FEM) with double-node, zero-thickness interface elements was developed and presented. This Part II paper includes the numerical solution of basic practical problems using both the staggered and the fully coupled approaches. A first group of simulations, based on the classical consolidation problem with an added vertical discontinuity, is used to compare both the approaches in terms of accuracy and convergence. The monolithic or fully coupled scheme is also used in an application example studying the influence of a horizontal joint in the performance of a reservoir subject to fluid extraction. Results include a comparison with other numerical solutions from the literature and a sensitivity analysis of the mechanical parameters of the discontinuity. Some simulations are also run using both a full non-symmetric and a simplified symmetric Jacobian matrix. On top of verifying the model developed and its capability to reflect the conductivity changes of the interface with aperture changes, the results presented also lead to interesting observations of the numerical performance of the methods implemented. Copyright © 2008 John Wiley & Sons, Ltd. [source] The probabilistic key-group methodINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2004A. R. Yarahmadi Bafghi Abstract Key-block approaches are widely used in the analysis of rock slopes. The key-group method improves such analyses by taking into account groups of blocks instead of single blocks. Nevertheless, these stability analyses are usually carried out within a context where uncertainty may be a difficult problem to overcome. In the present paper, we propose introducing probabilistic approaches into the key-group method in order to account for uncertainty in the mechanical parameters of the problem to be solved. Both the first-order, second-moment method (FOSM) and the advanced second-moment method (ASMM) are considered herein and compared with Monte-Carlo simulations through the use of five theoretical case studies. Lastly, the probabilistic key-group method (PKGM) is qualified. Copyright © 2004 John Wiley & Sons, Ltd. [source] Determining soil permeability from pressuremeter testsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 1 2003D. Rangeard This paper presents a methodology for identifying soil permeability from pressuremeter test. On the first part we present a numerical analysis of the permeability effects on the test results. We demonstrate that different drainage conditions arise during test, as a function of the loading rate and the soil permeability. We also studied the pore pressure dissipation during strain holding stages. Based on this analysis of these tests, we propose a general procedure to identify simultaneously mechanical parameters and permeability from pressuremeter tests with strain holding test stages. This procedure was applied on tests performed on natural Saint,Herblain clay. An apparatus called pressio-triax was developed for this purpose. The values of the mechanical parameters as well as of the permeability value were found to agree very well with the values of the same parameters obtained from conventional laboratory tests. Copyright © 2002 John Wiley & Sons, Ltd. [source] How do COPD and healthy-lung patients tolerate the reduced volume ventilation strategy during OLV ventilation.ACTA ANAESTHESIOLOGICA SCANDINAVICA, Issue 9 2010P. MICHELET Background: Although a strategy of tidal volume (Vt) reduction during the one-lung ventilation (OLV) period is advised in thoracic surgery, the influence of the pre-operative respiratory status on the tolerance of this strategy remains unknown. Therefore, the aim of this study was to compare the pulmonary function between chronic obstructive pulmonary disease (COPD) and healthy-lung patients during the operative and the post-operative period. Methods: Forty-eight patients undergoing a planned lobectomy for cancer and presenting either a healthy lung function (n=24) or a moderate COPD stage (n=24) were ventilated without external positive end-expiratory pressure (PEEP) and received 9 ml/kg Vt during the two-lung ventilation (TLV) period, secondary reduced to 6 ml/kg during the OLV period. Lung function was assessed by peroperative gas exchange, venous admixture, respiratory mechanical parameters and post-operative spirometric measurements. Results: Although the PaO2 was superior in the healthy-lung group during the TLV, once the OLV was established, no difference was observed between the two groups. Moreover, the PaO2/FiO2 was proportionally more impaired in the healthy-lung group compared with the COPD group (50 ± 13 vs. 72 ± 19% of the baseline values after exclusion and 32 ± 15 vs. 51 ± 25% after the thoracotomy, P<0.05 for each) as well as the venous admixture. In the post-operative period, a higher decrease was observed in the healthy-lung group for the forced vital capacity and the forced expiratory volume. Conclusions: Reducing Vt to 6 ml/kg without the adjunction of external PEEP during OLV is associated with better preservation of lung function in the case of moderate COPD than in the case of healthy-lung status. [source] Change of properties during storage of a UDMA/TEGDMA dental resinJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 2 2004Jong Keun Lee Abstract The aim of this study was to evaluate the changes in viscoelastic properties of a UDMA-based dental resin as a function of time after initial light exposure. Specimens of a UDMA/TEGDMA (70:30 wt%) resin were irradiated by a visible-light-curing unit. Immediately after the irradiation, the light-cured specimen was stored in the dark for different times from 1 to 120 h at 37 °C, and characterized by means of DMA, DSC, and FTIR spectroscopy. The irradiated specimen exhibited a bimodal shape in the form of two rapid declines in log E, corresponding to glass transition with a plateau between the two declines. Two distinct peaks were seen in tan , versus temperature. The thermal reaction of the incompletely cured sample with residual groups trapped by the fast reaction during irradiation is responsible for the plateau. After storage, significant changes were observed in dynamic mechanical parameters, DSC exotherm, and degree of conversion. Storage modulus continued to increase during the 4 h of storage and leveled off thereafter. Peak heights of tan , versus temperature were also influenced by storage. Degree of conversion increased from 75 ± 2% immediately after irradiation to 87 ± 3% after 120 h storage. The changes of the properties of this dental resin system when stored at 37 °C after irradiation are clinically important in terms of stability, durability, and performance after initial polymerization. © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 68B: 216,221, 2004 [source] Mechanical implications of estrogen supplementation in early postmenopausal womenJOURNAL OF BONE AND MINERAL RESEARCH, Issue 6 2010Felix W Wehrli Abstract Whereas the structural implications of drug intervention are well established, there are few data on the possible mechanical consequences of treatment. In this work we examined the changes in elastic and shear moduli (EM and SM) in a region of trabecular bone in the distal radius and distal tibia of early postmenopausal women on the basis of MRI-based micro-finite-element (µFE) analysis. Whole-section axial stiffness (AS) encompassing both trabecular and cortical compartments was evaluated as well. The study was conducted on previously acquired high-resolution images at the two anatomic sites. Images were processed to yield a 3D voxel array of bone-volume fraction (BVF), which was converted to a µFE model of hexahedral elements in which tissue modulus was set proportional to voxel BVF. The study comprised 65 early postmenopausal women (age range 45 to 55 years), of whom 32 had chosen estrogen supplementation (estradiol group); the remainder had not (control group). Subjects had been scanned at baseline and 12 and 24 months thereafter. At the distal tibia, EM and SM were reduced by 2.9% to 5.5% in the control group (p,<,.05 to <.005), but there was no change in the estradiol subjects. AS decreased 3.9% (4.0%) in controls (p,<,.005) and increased by 5.8% (6.2%) in estradiol group subjects (p,<,.05) at 12 (24) months. At the distal radius, EM and SM changes from baseline were not significant, but at both time points AS was increased in estradiol group subjects and decreased in controls (p,<,.005 to <.05), albeit by a smaller margin than at the tibia. EM and SM were strongly correlated with BV/TV (r2,=,0.44 to 0.92) as well as with topologic parameters expressing the ratio of plates to rods (r2,=,0.45 to 0.82), jointly explaining up to 96% of the variation in the mechanical parameters. Finally, baseline AS was strongly correlated between the two anatomic sites (r2,=,0.58), suggesting that intersubject variations in the bone's mechanical competence follows similar mechanisms. In conclusion, the results demonstrate that micro-MRI-based µFE models are suited for the study of the mechanical implications of antiresorptive treatment. The data further highlight the anabolic effect of short-term estrogen supplementation. © 2010 American Society for Bone and Mineral Research [source] APPLICATION OF A COMPRESSION-RELAXATION TEST FOR THE CHARACTERIZATION OF BURLAT SWEET CHERRYJOURNAL OF TEXTURE STUDIES, Issue 1 2001PEDRO L. MARQUINA Mechanical parameters of Burlat sweet cherries (Prunus avium) were studied as a function of ripening during three consecutive years by using a penetration test, a compression test between two plates, and a compression-relaxation test. The latter yields the "apparent secant modulus," i. e. the ratio of the initial maximum compression force over the applied strain. This modulus is one of the most useful mechanical parameters to discriminate between batches because its value is clearly related to the variety and degree of ripeness. Thus, the compression-relaxation test consistently allowed the differentiation of cherries in five degrees of ripeness. [source] VARIATIONS IN FLEXURAL AND COMPRESSIVE FRACTURE BEHAVIOR OF A BRITTLE CELLULAR FOOD (DRIED BREAD) IN RESPONSE TO MOISTURE SORPTIONJOURNAL OF TEXTURE STUDIES, Issue 5 2000Y. P. CHANG Mechanical properties of dried bread (a cellular baked product) equilibrated at different water activities (Aw) were measured using three-point bending and uniaxial compression to compare their responses to moisture sorption. The glass-to-rubber transition was clearly demarcated in all the mechanical property-Aw curves, although there were differences in critical Aw (0.32,0.56) at which the dramatic changes in mechanical properties occurred. The role of water appeared to be strictly that of a plasticizer where flexural mechanical parameters were concerned, leading to reduced modulus and fracture stress but increased fracture strain with increasing Aw. Uniaxial compression tests revealed moisture-induced mechanical antiplasticization effects on the material in the glassy state which resulted in maximum compressive fracture stress but minimum fracture strain over the Aw range from 0,0.56. Compressive modulus apparently was not affected much by moisture sorption up to an Aw of 0.43, above which it decreased sharply. [source] Analysis of the possibility to control complex semiconductors properties by shock wave treatmentPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2003Vitaly Yakovyna Abstract This paper is dedicated to the experimental investigation of laser-induced shock waves impact on electrical, photoelectric and mechanical parameters of narrow-gap Hg1,xCdxTe alloys. A mechanism of defect structure rebuilding under the laser shock waves effect is developed. The proposed mechanism manifests itself in one of two dominant ways depending upon the processing mode. The two modes considered involve inducing shock waves by either a single laser pulse or a multi-spike laser pulse. [source] A metabolic approach to the treatment of dilated cardiomyopathy in BIO T0,2 cardiomyopathic Syrian hamstersBIOFACTORS, Issue 1-4 2005Rino Mancinelli Abstract Mechanisms underlying dilated cardiomyopathy (DCM) are poorly understood and effective therapy is still unavailable. The aim of this study was to examine the heart ultrastructure and dynamic of BIO T0,2 cardiomyopathic hamsters, an animal model of DCM, and to study in these animals, the effects of a co-formulation (HS12607) of propionyl-L-carnitine, coenzyme Q10 and omega-3 fatty acids on cardiac mechanical parameters. Sarcomere length, Frank-Starling mechanism and force-frequency relations were studied on isolated ventricular papillary muscle from age-matched BIO F1B normal Syrian hamsters, BIO T0,2 control and BIO T0,2 HS12607-treated cardiomyopathic Syrian hamsters. At the optimum length to maximum active force, electron microscopy of left ventricular papillary muscle revealed that seven out of ten muscles studied showed shorter sarcomeres (1.20 ± 0.29,m), and the remaining three showed longer sarcomeres (2.80 ± 0.13,m), compared to those of normal hamsters (2.05± 0.06,m, n=10). Severe alterations of the Frank-Starling mechanism, force-frequency relations and derivative parameters of contractile waves were also observed in vitro in the BIO T0,2 control hamsters. Long-term (8 weeks) treatment with HS12607 prevented alterations in sarcomere length in the BIO T0,2 cardiomyopathic hamsters; the Frank-Starling mechanism and force-frequency relations were also significantly (P<0.05) improved in these hamsters. Therefore results of the present study strongly suggest the need for clinical studies on metabolic therapeutic intervention in the effort to stop the progression of dilated cardiomyopathy. [source] | |||||||||||||