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Bending Stresses (bending + stress)
Selected AbstractsA method for measuring bending stresses based on electromagnetic actuation and Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2007Yongfeng Ren Abstract Bending stress and fracture strength of micromachined structures are the parameters determining the function and life span of microelectromechanical systems (MEMS) and are also indispensable data for MEMS design. This paper reports the results of a study in which a bending stress measurement method based on electromagnetic actuation and Raman spectroscopy has been examined. In this study, an eight-cantilever mass structure is chosen as the experimental object. The results have indicated that it can accurately measure the bending stresses and fracture strength. Copyright © 2006 John Wiley & Sons, Ltd. [source] Strength estimation of ceramic,metal joints with various interlayer thicknessFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2003M. TAKAHASHI ABSTRACT Residual stresses generated by the mismatch of thermal expansion coefficients of ceramics and metals affect the strength of ceramic,metal joints. An interlayer metal can be inserted between the ceramic and metal in order to relax this stress. An analysis was carried out of the residual stresses produced during joint-cooling and in 4-point bending tests. The effects of interlayer thickness on ceramic,metal joint strength were then studied by considering a superimposed stress distribution of the residual stress and the bending stress. Finally, joint strength was estimated from fracture mechanics and strength probability analysis by considering the residual stress distribution, defect size and position of pre-existing defects in the ceramic parts. As a result of this study, we suggest an optimum material selection and interlayer thickness for ceramic,metal joint structures. This approach is generally suitable for the design of electrical and mechanical structures. [source] Processing of urea-formaldehyde-based particleboard from hazelnut shell and improvement of its fire and water resistanceFIRE AND MATERIALS, Issue 8 2009M. Gürü Abstract The purpose of this study was to manufacture urea-formaldehyde-based particleboard from hazelnut shell and eliminate its disadvantages such as flammability, water absorption, swelling thickness by using fly ash and phenol-formaldehyde. Synthesized urea-formaldehyde and grained hazelnut shells were blended at different ratios ranging from 0.8 to 3.2 hazelnut shell/urea-formaldehyde and dried at 70°C in an oven until constant weight was reached. In addition, other parameters affecting polymer composite particleboard from hazelnut shell and urea-formaldehyde were investigated to be the amount of fly ash, amount of phenol formaldehyde and the effects of these parameters on bending stress, limit oxygen index, water absorption capacity and swelling in the thickness. The optimization results showed that the maximum bending strength was 4.1N/mm2, at urea-formaldehyde ratio of 1.0, reaction temperature of 70°C, reaction time of 25,min, hazelnut shell/urea-formaldehyde resin of 2.4 and mean particle size of 0.1,mm. Although the limited oxygen index and smoke density of composite particleboard without fly ash has 22.3 and 1.62, with fly ash of 16% (w/w) according to the filler has 38.2 and 1.47, respectively. Water absorption and increase in the swelling thickness exponentially decreased with increasing phenol formaldehyde. Copyright © 2009 John Wiley & Sons, Ltd. [source] Regional variation of intracortical porosity in the midshaft of the human femur: age and sex differencesJOURNAL OF ANATOMY, Issue 2 2005C. David L. Thomas Abstract This study investigated age and sex differences in patterns of porosity distribution in the midshaft of the human femur. Cross-sections were obtained from 168 individuals from a modern Australian population. The sample comprised 73 females and 95 males, aged between 20 and 97 years. Microradiographs were made of 100-µm sections and pore and bone areas were determined using image processing software. Initially the sample was divided by age: young (20,44 years), middle (45,64 years) and old (65+ years), but it was found that analysis on the basis of the ratio of medullary area to total subperiosteal area gave clearer results. The cortex was divided into three rings radially and into octants circumferentially and the porosity of each segment was calculated. Results showed that a pattern with raised porosity in the posterior and anterolateral regions, and with greater porosity in the inner parts of the cortex, becomes more pronounced with age. In males this pattern develops steadily; in females there are much greater differences between the middle and older groups than earlier in life. The patterns observed are consistent with progressive bone loss occurring along a neutral axis of the cortex where bending stress is lowest and the mechanical advantage of the bone is least. [source] Rissbildung von biegebeanspruchten Bauteilen aus Ultrahochfestem FaserbetonBETON- UND STAHLBETONBAU, Issue 9 2009Günter Heinzle Dipl.-Ing. Versuche; Berechnungs- und Bemessungsverfahren Abstract Das Konstruieren und Bemessen von Bauwerken aus faserbewehrtem UHPC erfordert sehr detailliertes Wissen über das Zugtragverhalten von Faserbeton. Es ist beeinflusst von der Fasergeometrie, der Fasermenge, der Schubverbundfestigkeit zwischen Faser und Matrix, der Matrixfestigkeit, dem Schwinden und der Faserorientierung. Leutbecher beschreibt ein Modell für reine Zugbeanspruchungen, indem all diese Parameter Eingang finden. Im hier vorliegenden Artikel wird dieses Modell für Biegebeanspruchungen erweitert und anhand von Biegeversuchen an Platten aus UHPC verifiziert. Dabei werden sowohl Faserbewehrung als auch konventionelle Stabbewehrung berücksichtigt. Crack Formation of Flexural Members made of UHPFRC For the design and planning of buildings made of fibre reinforced ultra high performance concrete one needs very detailed knowhow about the tensile carrying behaviour of fibrated concrete. It is affected by various parameters such as the fibre geometry, the content of fibres, the bond strength between fibre and binder matrix, the strength of the matrix, the shrinkage of the concrete and the orientation of the fibres. All these parameters are considered in a theoretical model for UHPFRC under tension (Leutbecher). In the paper presented here the range of validity of this model is extended to bending stress. Experimental investigations on UHPC-plates under bending complete and verify the theoretical results. The tests cover fibre reinforcement as well as conventional passive reinforcement. [source] Instability investigation of cantilevered seacliffsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2008Adam P. Young Abstract Wave action is a fundamental mechanism in seacliff erosion, whereby wave undercutting creates an unstable cantilevered seacliff profile and can lead to large catastrophic cliff failures, thus threatening coastal infrastructure. This study investigated the instability of two such failures that occurred in Solana Beach, California, by combining terrestrial LIDAR scanning, cantilever beam theory and finite element analysis. Each landslide was detected by evaluating the surface change between subsequent high resolution digital terrain models derived from terrestrial LIDAR data. The dimensions of failed cantilever masses were determined using the surface change measurements and then incorporated into failure stress analysis. Superimposing stress distributions computed from elastic cantilever beam theory and finite element modeling provided a method to back-calculate the maximum developed tensile and shear stresses along each failure plane. The results of the stress superposition revealed that the bending stresses caused by the cantilevered load contributed the majority of stress leading to collapse. Both shear and tensile failure modes were investigated as potential cliff failure mechanisms by using a comparison of the back-calculated failure stresses to material strengths found in laboratory testing. Based on the results of this research, the tensile strength of the cliff material was exceeded at both locations, thus causing the cliffs to collapse in tension. Copyright © 2008 John Wiley & Sons, Ltd. [source] Fully Flexible Solution-Deposited ZnO Thin-Film TransistorsADVANCED MATERIALS, Issue 38 2010Keunkyu Song Solution-processed, fully flexible ZnO thin-film transistors (TFTs) on semitransparent substrates are demonstrated. Our devices show exceptional and unprecedented stablity against various bending stresses, i.e., bending, rolling, wearing, and folding, exhibiting no degradation at tensile strains up to 6.35%. [source] Periapical biomechanics and the role of cyclic biting force in apical retrograde fluid movementINTERNATIONAL ENDODONTIC JOURNAL, Issue 9 2005A. Kishen Abstract Aim, To investigate the stress distribution pattern in the periapical region caused by biting forces and to study the role of cyclic biting loads on periapical fluid movement. Methodology, In the first part, a digital photoelastic experiment was conducted to study stress distribution in the periapical region. In the second, 20 maxillary central incisors were selected and divided into three main groups: normal intact teeth (group 1), tooth specimens in which the root canal was enlarged and maintained wet (group 2), and tooth specimens in which the root canal was enlarged and maintained dry (group 3). The tooth specimens were placed in a polycarbonate support with a cavity filled with a sponge soaked in methylene blue solution to simulate a periapical defect with exudate. During testing, the specimens were placed in a water bath at 37 °C, and were loaded cyclically with a load of 20 N, at a rate of 72 cycles min,1, to a maximum of 20 000 cycles. The specimens were then sectioned and evaluated for retrograde fluid movement using light microscopy. The data were analysed using one-way anova (post hoc tests). Results, Digital photoelastic experiments showed that the compression of teeth produced bending stresses in the periapical region. Testing with cyclic loads demonstrated retrograde fluid movement into the apical portion of the root canal and extraradicular region in all groups. There was a significant difference amongst the apical retrograde fluid movement displayed by different groups (<0.01). Group 2, in which the root canal was enlarged and maintained wet showed maximum retrograde fluid movement, whilst group 3, in which the root canal was enlarged and maintained dry showed the least retrograde fluid movement. Conclusions, Biting forces would cause bending of the periapical bone and cyclic biting forces would contribute to retrograde fluid movement into the root canal space and extraradicular region. [source] Optimal setpoint chasing in dynamic positioning of deep-water drilling and intervention vesselsINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 13 2001Asgeir J. Sørensen Abstract Conventional controller designs for dynamic positioning of ships and floating marine structures have so far been based on the principle on automatic positioning in the horizontal-plane about desired position and heading co-ordinates defined by the operator. A three degrees-of-freedom multivariable controller either of linear or nonlinear type, normally with feedback signals from surge, sway and yaw position and velocities, has been regarded as adequate for the control objective. For floating structures with small waterplane area such as semi-submersibles, feedback from roll and pitch angular rotation velocity may also be included to avoid thrust-induced roll and pitch motions that are caused by the hydrodynamic and the geometrical couplings between the horizontal and vertical planes. However, for certain marine operations this control philosophy may not be the most appropriate approach ensuring safety and cost effectiveness. For drilling and work-over operations the main positioning objective is to minimize the bending stresses along the riser and the riser angle magnitudes at the well head on the subsea structure, and at the top joint as well. A positioning control strategy solely based on manual setting of the desired position co-ordinates may not be the most optimal solution for these applications. In this paper a new hybrid dynamic positioning controller, that also accounts for riser angle offsets and bending stresses is proposed. It is shown that a significant reduction in riser angle magnitude can be achieved. Simulations with a drilling semi-submersible demonstrate the effect of the proposed control strategy. Copyright © 2001 John Wiley & Sons, Ltd. [source] A method for measuring bending stresses based on electromagnetic actuation and Raman spectroscopyJOURNAL OF RAMAN SPECTROSCOPY, Issue 2 2007Yongfeng Ren Abstract Bending stress and fracture strength of micromachined structures are the parameters determining the function and life span of microelectromechanical systems (MEMS) and are also indispensable data for MEMS design. This paper reports the results of a study in which a bending stress measurement method based on electromagnetic actuation and Raman spectroscopy has been examined. In this study, an eight-cantilever mass structure is chosen as the experimental object. The results have indicated that it can accurately measure the bending stresses and fracture strength. Copyright © 2006 John Wiley & Sons, Ltd. [source] Relative fatigue life estimation of cylindrical hollow rollers in general pure rolling contactLUBRICATION SCIENCE, Issue 1 2008Wisam M. Abu Jadayil Solid and hollow cylindrical rollers in pure rolling contact have been modelled. The two rollers are subjected to a combined normal and tangential loading. The tangential loading is one-third of the normal loading value. The finite element package, ABAQUS, is used to study the stress distribution and the resulting deformations in the bodies of the rollers. Then the Ioannides,Harris fatigue life model for rolling bearings is applied on the ABAQUS numerical results to investigate the fatigue life of the solid and hollow rollers. Using the fatigue life of the solid rollers as the reference fatigue life, the relative fatigue lives of hollow rollers are determined. Four main different hollowness percentages are been studied: 20, 40, 60 and 80%. The hollowness percentage is the ratio of the diameter of the hole to the outer diameter of the cylinder. For each of those hollowness percentages, two cases are studied , when the two rollers in contact are hollow and when one hollow roller is in contact with a solid roller. This study includes two main models: Model 1, where the two cylindrical rollers in contact are of the same size, and Model 2, where the two rollers in contact are not of the same size. The estimated relative fatigue lives of hollow rollers showed a great improvement of the fatigue life compared with solid rollers under the same loading conditions. This was a result of the redistribution of stresses in the contact zone in the case of hollow rollers. Redistribution of stresses over a larger volume of the roller body decreased the peak stress and reduced the volume under risk. Increasing the hollowness percentage from 20 to 60% increased the flexibility of the roller, and better stress distribution was achieved, which resulted in improving the fatigue life. Although 80% of hollowness rollers have more flexibility than 60% of hollowness rollers, the bending stresses (,b) on the inner surface of the rollers tend to decrease the fatigue life. Copyright © 2007 John Wiley & Sons, Ltd. [source] | |||||||||||||