Home About us Contact
|
Home About us Contact | ||
|
|
||
Failure Load (failure + load)
Selected AbstractsJoint properties of cast Fe-Pt magnetic alloy laser welded to gold alloysJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2006Ikuya Watanabe Abstract This study investigated the joint properties of a cast Fe-Pt magnetic alloy (Fe-36 at % Pt) laser welded to three gold alloys. The gold alloys used were ADA Type II and Type IV gold alloys, and an Ag-based (Ag-Au) gold alloy. Cast plates (0.5 × 3.0 × 10 mm) were prepared for each alloy. After the cast Fe-Pt plates were heat treated, they were butted against each of the three alloys and then laser welded with Nd:YAG laser at 200 V. Homogeneously welded specimens were also prepared for each alloy. Tensile testing was conducted at a crosshead speed of 1 mm/min. Failure load (N) and elongation (%) were recorded. After tensile testing, the fractured surfaces were examined with the use of SEM. The failure-load values of the group of alloys welded homogeneously were ranked in the order of: Ag-Au alloy > Type IV alloy > Type II alloy > Fe-Pt alloy. The Type IV alloy welded to Fe-Pt alloy had the highest failure-load value among the three alloys tested. The elongation results tended to follow a similar pattern. The results of this study indicated that Type IV gold alloy is a suitable alloy for metal frameworks to which cast Fe-Pt magnetic alloy is laser welded. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source] Fracture Resistance of Endodontically Treated Teeth: Three Walls versus Four Walls of Remaining Coronal Tooth StructureJOURNAL OF PROSTHODONTICS, Issue 1 2009Siriporn Arunpraditkul DDS Abstract Purpose: The purpose of this study was to evaluate the fracture resistance of endodontically treated teeth between those with four walls and those with three walls of remaining coronal tooth structure and the effect of the site of the missing coronal wall. Materials and Methods: Thirty-two endodontically treated second mandibular premolars were decoronated, leaving 3 mm above the cementoenamel junction (CEJ). A 0.5-mm-wide chamfer was prepared 1 mm above the CEJ. The teeth were randomly divided into four groups. Group 1 had four walls of coronal tooth structure, whereas groups 2, 3, and 4 had only three walls, missing the buccal, lingual, and mesial wall, respectively. The cast dowel and cores and crowns (Ni,Cr alloy) were cemented with zinc phosphate cement. A compressive load was applied 45° to the long axis, 2 mm below the buccal cusp, with an Instron machine until failure at a crosshead speed of 5 mm/min. Failure load (kg) and mode of failure were recorded. Data were analyzed with one-way ANOVA and Scheffé tests (p < 0.05). Results: Group 1 had the highest fracture resistance (1190.3 ± 110.5 kg), significantly different from the other groups (p < 0.05) (group 2: 578.5 ± 197.4 kg; group 3: 786.6 ± 132.8 kg; group 4: 785.4 ± 289.9 kg). There were no significant differences among the test groups. The mode of failure in group 1 was a horizontal root fracture, whereas that of the other groups was either vertical or oblique fracture. Conclusions: Teeth with four walls of remaining coronal dentine had significantly higher fracture resistance than teeth with only three walls. The site of the missing coronal wall did not affect the fracture resistance of endodontically treated teeth. [source] Numerical and experimental investigation of mixed-mode fracture parameters on silicon nitride using the Brazilian disc testFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2010G. LEVESQUE ABSTRACT Engineering applications of ceramics can often involve mixed-mode conditions involving both tensile and shear loading. Mixed-mode fracture toughness parameters are evaluated for applicability to ceramics using the Brazilian disc test on silicon nitride. Semi-elliptical centrally located surface flaws are induced on the disc specimens using Vickers indentation and compression loaded to fracture with varying levels of mode mixity. The disc specimens are modelled via 3D finite element analysis and all three modes of stress intensity factors computed along the crack front, at failure load. We present a numerical and experimental investigation of four widely used mixed-mode fracture criteria and conclude that the critical strain energy release rate criterion is simple to implement and effective for silicon nitride under mixed-mode conditions. [source] Application of interface finite elements to three-dimensional progressive failure analysis of adhesive jointsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 5 2003J. P. M. GONÇALVES ABSTRACT The paper presents a new model for three-dimensional progressive failure analysis of adhesive joints. The method uses interface elements and includes a damage model to simulate progressive debonding. The interface finite elements are placed between the adherents and the adhesive. The damage model is based on the indirect use of fracture mechanics and allows the simulation of the initiation and growth of damage at the interfaces without considering the presence of initial flaws. The application of the model to single lap joints is presented. Experimental tests were performed in aluminium/epoxy adhesive joints. Linear elastic and elastoplastic analyses were performed and the predicted failure load for the elastoplastic case agrees with experimental results. [source] Engineering Strong Intergraphene Shear Resistance in Multi-walled Carbon Nanotubes and Dramatic Tensile ImprovementsADVANCED MATERIALS, Issue 5 2010Mehdi Estili Strong intergraphene shear resistance is engineered in multi-walled carbon nanotubes (MWCNTs) by embedding the nanotubes into a compressive-stressing ceramic environment to exploit the exceptional strength of its inner graphene walls during tensile loading. A dramatic enhancement in the tensile failure load of MWCNT is achieved in the ceramic environment and a new "multi-wall" failure mechanism is discovered. [source] Bearing capacity of two interfering footingsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 3 2008Jyant Kumar Abstract By using an upper bound limit analysis in conjunction with finite elements and linear programming, the ultimate bearing capacity of two interfering rough strip footings, resting on a cohesionless medium, was computed. Along all the interfaces of the chosen triangular elements, velocity discontinuities were employed. The plastic strains were incorporated using an associated flow rule. For different clear spacing (S) between the two footings, the efficiency factor (,,) was determined, where ,, is defined as the ratio of the failure load for a strip footing of given width in the presence of the other footing to that of a single isolated strip footing having the same width. The value of ,, at S/B = 0 becomes equal to 2.0, and the maximum ,, occurs at S/B = ,Scr/B. For S/B,Scr/B, the ultimate failure load for a footing becomes almost half that of an isolated footing having width (2B + S), and the soil mass below and in between the two footings deforms mainly in the downward direction. In contrast, for S/B>Scr/B, ground heave was noticed along both the sides of the footing. As compared to the available theories, the analysis provides generally lower values of ,, for S/B>Scr/B. Copyright © 2007 John Wiley & Sons, Ltd. [source] Tendon surface modification by chemically modified HA coating after flexor digitorum profundus tendon repairJOURNAL OF BIOMEDICAL MATERIALS RESEARCH, Issue 1 2004Chao Yang Abstract Carbodiimide derivatized HA (cd-HA) is less soluble in water than normal HA, and therefore has an increased tissue residence time. The purpose of this study was to study the effect of cd-HA gel on gliding and repair integrity during simulated repetitive motion of a repaired tendon in vitro. A total of 36 flexor digitorum profundus (FDP) tendons from six adult mongrel dogs were used and divided into three groups of control, simple HA, and cd-HA. The gliding resistance between the FDP and the proximal pulley, FDS, and bone was measured before laceration and after modified Kessler technique repair at 1, 5, 10, 50, 100, 200, 300, 400, and 500 cycles. After gliding testing, failure load, tendon stiffness, and resistance to gap formation were measured. The results showed from the first cycle to the 10th cycle, there were no significant differences in gliding resistance between the three testing groups (p > 0.05). From the 50th cycle onwards, the friction was significantly lower in the cd-HA gel group than in the control group (p < 0.05). Neither breaking strength, nor tendon stiffness, nor resistance to gap formation of the repairs were significantly different between the three groups (p > 0.05). © 2003 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 68B: 15,20, 2004 [source] Rutin Inhibits Ovariectomy-Induced Osteopenia in RatsJOURNAL OF BONE AND MINERAL RESEARCH, Issue 11 2000Marie-Noëlle Horcajada-Molteni Abstract Several studies suggest that polyphenols might exert a protective effect against osteopenia. The present experiment was conducted to observe the effects of rutin (quercetin-3- O -glucose rhamnose) on bone metabolism in ovariectomized (OVX) rats. Thirty 3-month-old Wistar rats were used. Twenty were OVX while the 10 controls were sham-operated (SH). Among the 20 OVX, for 90 days after surgery 10 were fed the same synthetic diet as the SH or OVX ones, but 0. 25% rutin (OVX + R) was added. At necropsy, the decrease in uterine weight was not different in OVX and OVX + R rats. Ovariectomy also induced a significant decrease in both total and distal metaphyseal femoral mineral density, which was prevented by rutin consumption. Moreover, femoral failure load, which was not different in OVX and SH rats, was even higher in OVX + R rats than in OVX or SH rats. In the same way, on day 90, both urinary deoxypyridinoline (DPD) excretion (a marker for bone resorption) and calciuria were higher in OVX rats than in OVX + R or SH rats. Simultaneously, plasma osteocalcin (OC) concentration (a marker for osteoblastic activity) was higher in OVX + R rats than in SH rats. High-performance liquid chromatography (HPLC) profiles of plasma samples from OVX + R rats revealed that mean plasma concentration of active metabolites (quercetin and isorhamnetin) from rutin was 9.46 + 1 ,M, whereas it was undetectable in SH and OVX rats. These results indicate that rutin (and/or its metabolites), which appeared devoid of any uterotrophic activity, inhibits ovariectomy-induced trabecular bone loss in rats, both by slowing down resorption and increasing osteoblastic activity. [source] Bone Structural and Mechanical Properties Are Affected by Hypotransferrinemia But Not by Iron Deficiency in MiceJOURNAL OF BONE AND MINERAL RESEARCH, Issue 2 2000Elise A. Malecki Abstract Hypotransferrinemia is a genetic defect in mice resulting in <1% of normal plasma transferrin (Tf) concentrations; heterozygotes for this mutation (+/hpx) have low circulating Tf concentrations. We used this mutant mouse in conjunction with dietary iron deficiency to study the influence of Tf and iron on bone structural and mechanical properties. Twenty-one weanling wild-type BALB/cj +/+ mice and 21 weanling +/hpx mice were fed iron-deficient or iron-adequate diets for 8 weeks. Twelve hpx/hpx mice were fed the iron-adequate diet. Hypotransferrinemia resulted in increased tibia iron and calcium concentrations, lower femur failure load, and extrinsic stiffness. Because the femurs of the hpx/hpx mice were disproportionately small, these bones actually had increased tissue material properties (ultimate stress [US] and modulus of elasticity) than those of wild-type mice. This is the first report on the effect of dietary iron deficiency on bone structural and mechanical properties. Dietary iron deficiency in +/+ and +/hpx mice decreased tibia iron concentrations but had no effect on tibia calcium and phosphorus concentrations or femur structural or mechanical properties. Because the bones of the hpx/hpx mice were small, but had superior tissue mechanical properties, we conclude that Tf is important for normal bone mineralization. (J Bone Miner Res 2000; 15: 271,277) [source] Early bone in-growth ability of alumina ceramic implants loaded with tissue-engineered boneJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 4 2006Yasuaki Tohma Abstract To enhance early bonding of an alumina ceramic implant to bone, we evaluated a method of seeding the implant surface with bone marrow mesenchymal cells that differentiated to osteoblasts and bone matrix prior to implantation. The usefulness of the method was evaluated in Japanese white rabbits. In our study, an alumina ceramic test piece loaded with differentiated osteoblasts and bone matrix by a tissue engineering technique was implanted into rabbit bones. Three weeks after the procedure, evaluation of mechanical bonding and histological examination were performed. Histological examination of the noncell-loaded implant surfaces showed no bone infiltration into the implant gap. However, the cell-loaded implant surfaces exhibited new bone infiltration into the implant gap with mechanical bonding. In the mechanical test, the average failure load was 0.60 kgf for the noncell-loaded side and 1.49 kgf for the cell-loaded side. Preculturing mesenchymal cells on the surface of the alumina ceramic prior to implantation increased the debonding strength by two and half times. The present findings indicate early bonding between the implant and bone three weeks after the procedure. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [source] Comparison of Repair Methods for Ceramic-Fused-to-Metal CrownsJOURNAL OF PROSTHODONTICS, Issue 5 2006Mutlu Özcan DMD Purpose: The objective of this study was to evaluate the effect of four repair methods on the fracture load of repaired ceramic-fused-to-metal crowns. Materials and Methods: Metal-ceramic crowns were fractured, and the failure load was measured. The fractured metal-ceramic crowns (n = 9) were assigned randomly to the following treatment groups: (1) hydrofluoric acid (9.5%) etching, (2) air-particle abrasion (50 ,m Al2O3), (3) silica coating (30 ,m SiOx), and (4) the application of a layer of glass fiber-reinforced composite (FRC) (thickness: 0.12 mm) on the repair surface. The crowns were repaired with a highly filled resin composite and subjected to 3 repair cycles (n = 27). All specimens were stored in water at 37°C for 24 hours and then thermocycled (6000 cycles, 5°C to 55°C). The fracture load values for final failure of intact and repaired crowns were measured with a universal testing machine, and failure types were recorded. Results: No significant differences ( p > 0.05) were found between the final failure values for the groups treated with 9.5% hydrofluoric acid (376 N) and airborne particle abrasion with either Al2O3 (432 N) or SiOx (582 N) followed by silanization, respectively. Significantly, higher ( p < 0.0001) final failure values (885 N) were obtained with the use of the FRC layer when compared with the other repaired groups. There was no significant difference ( p > 0.05) between the final fracture load of intact crowns (872 N) and those repaired with FRC (885 N) (One-way ANOVA with repeated measures, Bonferroni test). No significant difference in fracture loads was found between the 1st, 2nd, and 3rd repair cycles (558 N, 433 N, 485 N, respectively). Failure sites were predominantly at the alloy/veneering resin interface in Group 1; Groups 2 and 3 both showed more cohesive failures than Group 1. In the case of FRC, the failure pattern was exclusively cohesive between the two laminates of FRC layer. Conclusions: The conditioning methods (Groups 1 to 3) of the repair surfaces did not show differences between each other; each resulted in mean fracture loads at lower levels than that of the intact crowns. Addition of an FRC layer increased the fracture load to the level of intact crowns. This suggests that the use of FRC in repairs of metal-ceramic crowns might be a viable option. [source] Bemessungsvorschlag für Holz/Beton-Verbundbalken unter Beachtung abgestufter VerbindungsmittelabständeBAUTECHNIK, Issue 3 2004Jörg Schmidt Dr.-Ing. Die Abstände der Verbindungsmittel von Holz/Beton-Verbundbalken werden i. allg. vorrangig aus Kostengründen entsprechend dem Querkraftverlauf abgestuft. Das Tragvermögen gemäß Bemessungsgrundlagen nach DIN 1052 bzw. EC 5 mit linear ermittelten Schnittgrößen (Näherungsverfahren/,-Verfahren) wird gegenüber Balken ohne die o. g. Abstufung deutlich reduziert. Da das tatsächliche Last-Verformungsverhalten jedoch deutliche Nichtlinearitäten aufweist und die Verbundsteifigkeit hinsichtlich des Tragvermögens nur einen geringen Einfluß besitzt, wird in diesem Beitrag der Einfluß der Abstufung der Verbindungsmittelabstände auf das Tragverhalten von Verbundbalken mittels nichtlinearer FE-Analysen untersucht. Im Ergebnis ist festzustellen, daß der Sicherheitsabstand zwischen Gebrauchslast gemäß E DIN 1052 und Versagenslastniveau mit zunehmendem Abstufungsgrad zunimmt, weil das tatsächliche Tragvermögen weniger , als durch das derzeitige Bemessungsmodell unterstellt , reduziert wird. Somit weisen also die Systeme, deren Verbinderabstände mehrmals abgestuft sind, den größten Sicherheitsabstand auf, könnten also noch wirtschaftlicher bemessen werden. Deshalb wird im Ergebnis der Untersuchungen ein neuer Bemessungsvorschlag unterbreitet und verifiziert, der die Nichtlinearitäten berücksichtigt, einen gleichmäßigen Sicherheitsabstand zum Versagenslastniveau gewährleistet und eine deutlich wirtschaftlichere Bemessung erlaubt. Design proposal for timber/concrete composite beams with graded connnector distances. The distance of connections of timber/concrete composite beams is often graded for economical reasons according the shear force distribution. The load-carrying capacity of composite beams according to DIN 1052 respectively E DIN 1052 with internal forces, which are linearly determined, (,-procedure) are clearly reduced compared to beams without graded distances of connectors. The actual load-bearing behaviour distinctly shows non-linearities. The influence of the gradations of the connectors on the load-bearing behaviour of composite beams is investigated, because the influence of the stiffness of connections on the load-bearing capacity of composite beams is small. The paper presents a comparison between failure loads determined by FE-analysis and the working loads according to the current design rule. It is shown that the decrease of load-bearing capacity is smaller than assumed by current code of practice. Structures with several different distances of connections have the largest safety-factor. These systems can more economically be designed. As the result of the investigations, a new design proposal is presented, which takes non-linearities into account and guarantees a constant safety-zone between failure load and working load. These proposal permits an economic design of timber/concrete composite beams. [source] In vitro fracture behavior of maxillary premolars with metal crowns and several post-and-core systemsEUROPEAN JOURNAL OF ORAL SCIENCES, Issue 3 2006Wietske A. Fokkinga The in vitro fracture behavior of severely damaged premolars, restored with metal crowns with limited ferrule and several post-and-core systems, was investigated. Crowns of maxillary premolars were removed and canals were prepared with Gates Glidden drills and with Parapost drills. Groups of 11 samples were each treated with cast post-and-cores (Parapost XP, Wironium Plus) (group 1), prefabricated metal posts (Parapost XH) (group 2), prefabricated glass fiber posts (Parapost FiberWhite) (group 3), and custom-made glass fiber posts (EverStick Post) (group 4). Posts and composite cores and metal crowns in groups 2, 3, and 4 were adhesively cemented. Post-and-cores and crowns in group 1 were cemented with phosphate cement. Thermocycling was performed (6,000×, 5,55 °C). Two static load tests (30°) were applied. During the first load test (preloading) no failures occurred. Failure modes from the second load test were categorized into favorable and unfavorable failures. Mean failure loads among the four groups (group 1, 1845 N; group 2, 1718 N; group 3, 1812 N; and group 4, 1514 N) were not significantly different. Unfavorable failures were root fractures and favorable failures were postcrown displacements. No differences in frequencies of unfavorable/favorable failures were seen among the groups. The results suggest that different post-and-core systems have no influence on the fracture behavior of severely damaged premolars restored with metal crowns with limited ferrule. [source] Association of Geometric Factors and Failure Load Level With the Distribution of Cervical vs.JOURNAL OF BONE AND MINERAL RESEARCH, Issue 6 2006Trochanteric Hip Fractures Abstract We experimentally studied the distribution of hip fracture types at different structural mechanical strength. Femoral neck fractures were dominant at the lowest structural strength levels, whereas trochanteric fractures were more common at high failure loads. The best predictor of fracture type across all failure loads and in both sexes was the neck-shaft angle. Introduction: Bone geometry has been shown to be a potential risk factor for osteoporotic fractures. Risk factors have been shown to differ between cervical and trochanteric hip fractures. However, the determinants of cervical and trochanteric fractures at different levels of structural mechanical strength are currently unknown. In addition, it is not known if the distribution of fracture types differs between sexes. The aim of this experimental study on excised femora was to investigate whether there exist differences in the distribution of cervical and trochanteric fractures between different structural mechanical strength levels and different sexes and to identify the geometric determinants that predict a fracture type. Materials and Methods: The sample was comprised of 140 cadavers (77 females: mean age, 81.7 years; 63 males: mean age, 79.1 years) from whom the left femora were excised for analysis. The bones were radiographed, and geometrical parameters were determined from the digitized X-rays. The femora were mechanically tested in a side impact configuration, simulating a sideways fall. After the mechanical test, the fracture patterns were classified into cervical and trochanteric. Results: The overall proportion of cervical fractures was higher in females (74%) than in males (49%) (p = 0.002). The fracture type distribution differed significantly across load quartiles in females (p = 0.025), but not in males (p = 0.205). At the lowest load quartiles, 94.7% of fractures in female and 62.5% in males were femoral neck fractures. At the highest quartiles, in contrast, only 52.6% of fractures in females and 33.3% in males were cervical fractures. Among geometric variables, the neck-shaft angle was the best predictor of fracture type, with higher values in subjects with cervical fractures. This finding was made in females (p < 0.001) and males (p = 0.02) and was consistent across all failure load quartiles. Conclusions: Femoral neck fractures predominate at the lowest structural mechanical strength levels, whereas trochanteric fractures are more common at high failure loads. Females are more susceptible to femoral neck fractures than males. The best predictor of fracture type across all structural strength levels and both sexes was the neck-shaft angle. [source] Bone Strength at Clinically Relevant Sites Displays Substantial Heterogeneity and Is Best Predicted From Site-Specific Bone DensitometryJOURNAL OF BONE AND MINERAL RESEARCH, Issue 1 2002Felix Eckstein Ph.D. Abstract In this study we test the hypotheses that mechanical bone strength in elderly individuals displays substantial heterogeneity among clinically relevant skeletal sites, that ex situ dual-energy X-ray absorptiometry (DXA) provides better estimates of bone strength than in situ DXA, but that a site-specific approach of bone densitometry is nevertheless superior for optimal prediction of bone failure under in situ conditions. DXA measurements were obtained of the lumbar spine, the left femur, the left radius, and the total body in 110 human cadavers (age, 80.6 ± 10.5 years; 72 female, 38 male), including the skin and soft tissues. The bones were then excised, spinal and femoral DXA being repeated ex situ. Mechanical failure tests were performed on thoracic vertebra 10 and lumbar vertebra 3 (compressive loading of a functional unit), the left and right femur (side impact and vertical loading configuration), and the left and right distal radius (fall configuration, axial compression, and 3-point-bending). The failure loads displayed only very moderate correlation among sites (r = 0.39 to 0.63). Ex situ DXA displayed slightly higher correlations with failure loads compared with those of in situ DXA, but the differences were not significant and relatively small. Under in situ conditions, DXA predicted 50-60% of the variability in bone failure loads at identical (or closely adjacent) sites, but only around 20-35% at distant sites, advocating a site-specific approach of densitometry. These data suggest that mechanical competence in the elderly is governed by strong regional variation, and that its loss in osteoporosis may not represent a strictly systemic process. [source] Generation of tendon-to-bone interface "enthesis" with use of recombinant BMP-2 in a rabbit modelJOURNAL OF ORTHOPAEDIC RESEARCH, Issue 11 2007Yusuke Hashimoto Abstract The anatomical structure at bone-tendon and bone-ligament interfaces is called the enthesis. Histologically, the enthesis is characterized by a transitional series of tissue layers from the end of the tendon to bone, including tendon, fibrocartilage, calcified fibrocartilage, and bone. This arrangement yields stronger direct connection of the soft tissues to bone. In surgical repair, the enthesis has proven difficult to reproduce, and the success of ligament-bone bonding has depended on the fibrous attachment that forms after any ligament reconstructions. In this study, we attempted to generate a direct-insertion enthesis in two stages. First, recombinant human bone morphogenetic protein-2 (rhBMP-2) was injected into the flexor digitorum communis tendon in the rabbit hind limb to induce ectopic ossicle formation. In a second step, the resultant tendon/ossicle complex was then surgically transferred onto the surface of the rabbit tibia to generate a stable tendon-bone junction. One month following surgery, histomorphological examination confirmed direct insertion of tendon-bone structures in the proximal tibia of the rabbit. Ultimate failure loads of the BMP-2-generated tendon-bone junction were significantly higher than in the control group (p,<,0.01). These findings suggest that it is possible to successfully regenerate a direct tendon-to-bone enthesis. Use of this approach may enable successful reconstruction of joints rendered unstable after ligamentous rupture or laxity after anterior cruciate ligament injury. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 25:1415,1424, 2007 [source] | ||||||||||||||||