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Load Transfer (load + transfer)
Selected AbstractsIn situ Study of Internal Load Transfer in a Novel Metal/Ceramic Composite Exhibiting Lamellar Microstructure Using Energy Dispersive Synchrotron X-ray Diffraction,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Siddhartha Roy Freeze casting offers a new technique to fabricate ceramic preforms for metal/ceramic composites. Internal load transfer under external compressive loading in such composites has been studied for the first time using energy dispersive synchrotron X-ray diffraction. The results show that load transfer takes place from the soft metallic alloy to the hard ceramic which has been explained in the light of generalized Hooke's law and classical laminate theory. [source] Influence of Attachment Systems on Load Transfer of an Implant-Assisted Maxillary OverdentureJOURNAL OF PROSTHODONTICS, Issue 4 2004Mete I. Fanuscu DDS Purpose: This photoelastic study compared the load transfer characteristics of 2 retention mechanisms in an implant-assisted overdenture prosthesis. Materials and Methods: Four implants were incorporated into a photoelastic model of a moderately resorbed edentulous human maxilla. Two retention mechanisms were studied by changing components on the same model and the palateless overdenture. The retention mechanisms studied were bar splint with anterior clip and distal resilient attachments, and solitary ball/O-ring attachments. Loads, ranging from 1.4 to 14.4 kg, were applied to the palatal incline of central incisors and buccal incline of premolars with and without balancing contacts. Stresses developed around all the implants under each loading condition were photographed in the field of a circular polariscope. Results: With both retention mechanisms, protrusive and laterotrusive loads without balancing contacts caused instability of the overdenture, producing minimal stress around the implants in the supporting structure. High intensity stresses indicating intrusion of the posterior implants were noted when the bar/distal resilient attachment overdenture had balancing contacts for protrusive and laterotrusive loads. The posterior implants of ball/O-ring attachment overdenture exhibited high intensity stresses indicating not only intrusion, but also bending, when the occlusion was balanced. Conclusions: Balanced occlusion was required in both retention mechanisms for stability of the implant-assisted overdenture when clinically acceptable loads were applied. The protrusive and laterotrusive loads were not distributed equitably in either mechanism, since highest stresses occurred at the posterior implants. [source] In situ Study of Internal Load Transfer in a Novel Metal/Ceramic Composite Exhibiting Lamellar Microstructure Using Energy Dispersive Synchrotron X-ray Diffraction,ADVANCED ENGINEERING MATERIALS, Issue 6 2009Siddhartha Roy Freeze casting offers a new technique to fabricate ceramic preforms for metal/ceramic composites. Internal load transfer under external compressive loading in such composites has been studied for the first time using energy dispersive synchrotron X-ray diffraction. The results show that load transfer takes place from the soft metallic alloy to the hard ceramic which has been explained in the light of generalized Hooke's law and classical laminate theory. [source] ,Arching' effect in elastic polycrystals: implications for the variability of fatigue livesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 4 2002S. Pommier ABSTRACT The paper deals with a study of heterogeneous stress and strain distribution in polycrystals in relation with elastic anisotropy of grains. A similitude with the arching effect widely studied in granular materials is proposed and this concept is extended to heterogeneous polycrystals in which the load transfer is not binary in the way it is in granular media but may vary significantly and suddenly from one grain to another according to the crystal orientation to the load direction. Experiments and 3D finite element analyses show that though the individual orientation of grains is random, the strain and stress distribution is not. A network is formed inside the polycrystal whose scale is larger than the grain size. The load percolation network consists in heavily loaded links whose direction is coincident with the direction of the principal stresses. So, the typical scale for the variability of the local stresses is not the grain size but the size of the load percolation network. Since this scale is found to be rather large in particular for iron, zinc and copper, this effect should contribute significantly to the variability of the fatigue lives of notched vs. smooth components. [source] Bonded aircraft repairs under variable amplitude fatigue loading and at low temperaturesFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 1 2000Vlot Bonded repairs can replace mechanically fastened repairs for aircraft structures. Compared to mechanical fastening, adhesive bonding provides a more uniform and efficient load transfer into the patch, and can reduce the risk of high stress concentrations caused by additional fastener holes necessary for riveted repairs. Previous fatigue tests on bonded Glare (glass-reinforced aluminium laminate) repairs were performed at room temperature and under constant amplitude fatigue loading. However, the realistic operating temperature of ,40 °C may degrade the material and will cause unfavourable thermal stresses. Bonded repair specimens were tested at ,40 °C and other specimens were tested at room temperature after subjecting them to temperature cycles. Also, tests were performed with a realistic C-5A Galaxy fuselage fatigue spectrum at room temperature. The behaviour of Glare repair patches was compared with boron/epoxy ones with equal extensional stiffness. The thermal cycles before fatigue cycling did not degrade the repair. A constant temperature of ,40 °C during the mechanical fatigue load had a favourable effect on the fatigue crack growth rate. Glare repair patches showed lower crack growth rates than boron/epoxy repairs. Finite element analyses revealed that the higher crack growth rates for boron/epoxy repairs are caused by the higher thermal stresses induced by the curing of the adhesive. The fatigue crack growth rate under spectrum loading could be accurately predicted with stress intensity factors calculated by finite element modelling and cycle-by-cycle integration that neglected interaction effects of the different stress amplitudes, which is possible because stress intensities at the crack tip under the repair patch remain small. For an accurate prediction it was necessary to use an effective stress intensity factor that is a function of the stress ratio at the crack tip Rcrack tip including the thermal stress under the bonded patch. [source] Molecular-Level Dispersion of Graphene into Poly(vinyl alcohol) and Effective Reinforcement of their NanocompositesADVANCED FUNCTIONAL MATERIALS, Issue 14 2009Jiajie Liang Abstract Despite great recent progress with carbon nanotubes and other nanoscale fillers, the development of strong, durable, and cost-efficient multifunctional nanocomposite materials has yet to be achieved. The challenges are to achieve molecule-level dispersion and maximum interfacial interaction between the nanofiller and the matrix at low loading. Here, the preparation of poly(vinyl alcohol) (PVA) nanocomposites with graphene oxide (GO) using a simple water solution processing method is reported. Efficient load transfer is found between the nanofiller graphene and matrix PVA and the mechanical properties of the graphene-based nanocomposite with molecule-level dispersion are significantly improved. A 76% increase in tensile strength and a 62% improvement of Young's modulus are achieved by addition of only 0.7,wt% of GO. The experimentally determined Young's modulus is in excellent agreement with theoretical simulation. [source] Assessment of conservative load transfer for fluid,solid interface with non-matching meshesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 15 2005R. K. Jaiman Abstract We present a detailed comparative study of three conservative schemes used to transfer interface loads in fluid,solid interaction simulations involving non-matching meshes. The three load transfer schemes investigated are the node-projection scheme, the quadrature-projection scheme and the common-refinement based scheme. The accuracy associated with these schemes is assessed with the aid of 2-D fluid,solid interaction problems of increasing complexity. This includes a static load transfer and three transient problems, namely, elastic piston, superseismic shock and flexible inhibitor involving large deformations. We show how the load transfer schemes may affect the accuracy of the solutions along the fluid,solid interface and in the fluid and solid domains. We introduce a grid mismatching function which correlates well with the errors of the traditional load transfer schemes. We also compare the computational costs of these load transfer schemes. Copyright © 2005 John Wiley & Sons, Ltd. [source] Analysis of load transfer and stress distribution by splinted and unsplinted implant-supported fixed cemented restorationsJOURNAL OF ORAL REHABILITATION, Issue 9 2010J. NISSAN Summary, Controversy remains over the rehabilitation of implant-supported restorations regarding the need to splint adjacent implant-supported crowns. This study compared the effects of simulated occlusal loading of three implants restored with cemented crowns, splinted versus unsplinted. Three adjacent screw-shaped implants were passively inserted into three holes drilled in a photo-elastic model. Two combinations of cemented restorations were fabricated; three adjacent unsplinted and three adjacent splinted crowns. Strain gauges were connected to the implant necks and to the margins of the overlaying crowns. Fifteen axial static loads of 20-kg loadings were carried out right after each other via a custom-built loading apparatus. Strain gauges located on the implant neck supporting splinted restoration demonstrated significantly (P < 0·001) more strain (sum of strains = 3348·54 microstrain) compared with the single crowns (sum of strains = 988·57 microstrain). In contrast, significantly (P < 0·001) more strain was recorded on the strain gauges located on the restoration margins of the single crowns (sum of strains = 756·32 microstrain) when compared with splinted restorations (sum of strains = 186·12 microstrain). The concept of splinting adjacent implants to decrease loading of the supporting structures may require re-evaluation. The clinical relevance of these findings needs further investigation. [source] The effects of partial and total interosseous membrane transection on load sharing in the cadaver forearmJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2001Michael F. Shepard This study was performed to examine the effects of partial and total transection of the interosseous membrane (IOM) on load transfer in the forearm. Twenty fresh frozen forearms were instrumented with custom designed load cells placed in the proximal radius and distal ulna. Simultaneous measurements of load cell forces, radial head displacement relative to the capitellum, and local tension within the central band of the IOM were made as the wrist was loaded to 134 N with the forearm at 90° of elbow flexion and in neutral pronation supination. For valgus elbow alignment (radial head contacting the capitellum), mean force carried by the distal ulna was 7.1% of the applied wrist force and mean force transferred from radius to ulna through the IOM was 4.4%. For varus elbow alignment (mean 2.0 mm gap between the radial head and capitellum), mean distal ulna force was 28% and mean IOM force was 51%. Section of the proximal and distal one-thirds of the IOM had no significant effect upon mean distal ulnar force or mean IOM force. Total IOM section significantly increased mean distal ulnar force for varus elbow alignment in all wrist positions tested. The mean level of applied wrist force necessary to close the varus gap (89 N) decreased significantly after both partial IOM section (71 N) and total IOM section (25 N). The IOM became loaded only when the radius displaced proximally relative to the ulna, closing the gap between the radius and capitellum. As the radius displaced proximally, the wrist becomes increasingly ulnar positive, which in turn leads to direct loading of the distal ulna. This shift of force to the distal ulna could present clinically as ulnar sided wrist pain or as ulnar impaction after IOM injury. © 2001 Orthopaedic Research Society. Punlished by Elsevier Science Ltd. All rights reserved. [source] Creep Resistant Polymer Nanocomposites Reinforced with Multiwalled Carbon NanotubesMACROMOLECULAR RAPID COMMUNICATIONS, Issue 8 2007Jinglei Yang Abstract Poly(propylene) (PP) nanocomposites filled with shorter- and longer-aspect-ratio multiwalled carbon nanotubes (MWNTs) were compounded using a twin-screw extruder and an injection moulding machine. It is shown that with only 1 vol.-% of MWNTs, creep resistance of PP can be significantly improved with reduced creep deformation and creep rate at a long-term loading period. Additionally, the creep lifetime of the nanocomposites has been considerably extended by 1,000% compared to that of a neat PP. Three possible mechanisms of load transfer were considered that could contribute to the observed enhancement of creep resistance, which are: (1) fairly good interfacial strength between MWNTs and polymer matrix, (2) increasing immobility of amorphous regions due to nanotubes acting as restriction sites, and (3) high aspect ratio of MWNTs. DSC results showing crystallinity changes in the specimens before and after creep deformation present evidence to confirm these mechanisms. Our results should lead to improved grades of creep resistant polymer nanocomposites for engineering applications. [source] Enhanced strength of portland cement products via reinforcing polypropylene/fiberglass structures obtained from a novel processing techniquePOLYMER COMPOSITES, Issue 5 2003Yuanheng Zhang An uninterrupted filament winding process was used to fabricate structures made of polypropylene and glass fiber that provide superior reinforcement to Portland cement structures. Fabricated polypropylene/fiberglass composite tubes were filled with a cement mixture and some were reinforced with internal tapes. Three-point bending experiments, microscopic observation, and image analysis were used as tools to study various processing variables and their effect on the mechanical properties of the tubes. The temperature of the mandrel and wetting strongly affected the composite's mechanical properties. Increased temperatures diminished the void content within the composite and produced a unique "fuzzy" inner surface for the cylindrical tube. The development of this "fuzzy" inner surface improved the strength and fatigue properties of the cement filled composite tube by providing efficient load transfer to the glass fibres. Also the surface to volume ratio of the steel rebar geometry when compared to that of the polypropylene/fibreglass structure explains the superior load transfer to the glass. It was found that a tube reinforced with 15 internal tapes filled with a cement mixture recorded a maximum tensile stress of 71 MPa (10,000 psi) with excellent damage tolerance, more than a 10-fold increase over the upper bound value for steel reinforced cement obtained from the rule of mixtures. The tube continued to be load bearing to strains of 0.4, which is more than 40 times the failure strain of glass. These large failure strains are the result of the shear yielding of polypropylene that coats the glass fibres and allows them to move within the cement. [source] Load transfer characteristics of unilateral distal extension removable partial dentures with polyacetal resin supporting componentsAUSTRALIAN DENTAL JOURNAL, Issue 1 2009T Jiao Abstract Background:, To photoelastically examine load transfer by unilateral distal extension removable partial dentures with supporting and retentive components made of the lower stiffness polyacetal resins. Methods:, A mandibular photoelastic model, with edentulous space distal to the right second premolar and missing the left first molar, was constructed to determine the load transmission characteristics of a unilateral distal extension base removable partial denture. Individual simulants were used for tooth structure, periodontal ligament, and alveolar bone. Three designs were fabricated: a major connector and clasps made from polyacetal resin, a metal framework as the major connector with polyacetal resin clasp and denture base, and a traditional metal framework I-bar removable partial denture. Simulated posterior bilateral and unilateral occlusal loads were applied to the removable partial dentures. Results:, Under bilateral and left side unilateral loading, the highest stress was observed adjacent to the left side posterior teeth with the polyacetal removable partial denture. The lowest stress was seen with the traditional metal framework. Unilateral loads on the right edentulous region produced similar distributed stress under the denture base with all three designs but a somewhat higher intensity with the polyacetal framework. Conclusions:, The polyacetal resin removable partial denture concentrated the highest stresses to the abutment and the bone. The traditional metal framework I-bar removable partial denture most equitably distributed force. The hybrid design that combined a metal framework and polyacetal clasp and denture base may be a viable alternative when aesthetics are of primary concern. [source] | |||||||||||||