Push-out Model Research Articles

Statistical modeling and safety analysis for developing design resistance of deconstructable HSFGB shear connectors in composite beam

In recent years, the high-strength friction-grip bolt (HSFGB) shear connectors in steel-concrete composite beams as deconstructable connectors are of great research interest since they are aligned with sustainable construction. However, the design strength equation for this type of connector has not yet been provided by the design codes such as AISC and Eurocode 4. In this paper, with regard to the reliability aspect, the design strength equation of HSFGB shear connectors is investigated which is projected into a partial safety factor according to Eurocode 4. Accordingly, the three-dimension finite element (FE) push-out model of the composite connection is developed and verified via experimental results to predict the load-slip behavior and failure modes in this type of bolted shear connector. Then One-Factor-at-a-Time (OFAT) method as a sensitivity analysis and Plackett-Burman (PB) design method as a screening analysis are utilized to identify the effective factors of the ultimate strength of HSFGB connectors. Finally, based on a complete database of all existing experimental findings, the results obtained from 55 three-dimension finite element models conducted in this paper, and appropriate statistical analysis, a high-precision equation for predicting ultimate strength is provided. Then the value of the partial safety factor is determined through a reliability study in accordance with EN1990, which provides an acceptable level of safety for the proposed design equation based on Eurocodes. Reliability analysis found that a partial factor of 1.52 was justified for the design strength of HSFGB connectors, which differed from the partial factor of 1.25 stated in the EC for welded stud shear connectors.

A uniform model of computational conceptual blending

We present a mathematical model for the cognitive operation of conceptual blending that aims at being uniform across different representation formalisms, while capturing the relevant structure of this operation. The model takes its inspiration from amalgams as applied in case-based reasoning, but lifts them into category theory so as to follow Joseph Goguen’s intuition for a mathematically precise characterisation of conceptual blending at a representation-independent level of abstraction. We prove that our amalgam-based category-theoretical model of conceptual blending is essentially equivalent to the pushout model in the ordered category of partial maps as put forward by Goguen. But unlike Goguen’s approach, our model is more suitable to capture computational realisations of conceptual blending, and we exemplify this by concretising our model to computational conceptual blends for various representation formalisms and application domains.

Bovine teeth can reliably substitute human dentine in an intra-tooth push-out bond strength model?

To investigate the reliability of using bovine teeth as an alternative to human teeth in an intra-tooth push-out model by comparing the bond strength of three root canal sealers in both tooth substrates. From human and bovine incisors (12 per group), one 1-mm disc was obtained from each root. On each disc, three standard 0.8-mm-diameter holes were drilled through the dentine. After irrigation, the holes were filled with one of three root canal sealers: AH Plus, MTA Fillapex or Total Fill BC Sealer. Tooth slices were kept in contact with sterile gauze moistened in PBS solution (pH=7.2) for 7days at 37°C, and finally, a push-out load was applied until sealer dislocation. The bonded interface area was calculated to obtain data in MPa. The push-out data for each sealer and the overall push-out data for human and bovine teeth were compared (Mann-Whitney U). Kruskal-Wallis was used to study the sealers behaviour at each of the dental substrates. Multiple comparisons were performed using Mann-Whitney U after Bonferroni correction (P<0.05). Dentine substrate did not influence the push-out of either individual sealers or overall sealers tested (Mann-Whitney U, P>0.05). In both human and bovine samples, AH Plus performed better than BC Sealer and MTA Fillapex, whilst BC Sealer also provided a superior push-out compared to MTA Fillapex (Mann-Whitney U, P<0.05). When using an intra-tooth model, bovine teeth did not significantly influence the bond strength of sealers.

Mechanism study on the low cycle fatigue behavior of group studs shear connectors in steel-concrete composite bridges

Clustering the stud shear connectors with a narrow spacing to form group studs is useful for the concrete slab prefabrication in steel-concrete composite bridges. But the existing test and analysis results have shown that arranging studs in group tends to be unfavorable to the stud static and fatigue performance. The current fatigue design of the group studs may still experience an overestimation or an underestimation problem since the fatigue mechanism study on group studs is rare. Therefore, a parametric push-out analysis was carried out for explaining the fatigue behavior of group studs, particularly the low cycle fatigue aspect with the fatigue life lower than 2millioncycles. There were 12 static and cyclic push-out models in the analysis. Meanwhile, a series of static push-out tests were also introduced to verify the analysis works. According to the static analysis results, the unequal stud shear forces in the group studs, which were indicated by the analyzed static failure mode, resulted in the reductions of stud shear stiffness and strength. According to the low cycle cyclic analysis results, the fatigue damage initiated at the bottom point of the stud root section in the push load direction, which can be called the fatigue critical point. The low cycle fatigue life reduction of group studs, which was evaluated by the analysis results and the introduced multi-axial fatigue damage criterion, can be explained by the uneven cyclic tensile strain and stress distributions on every individual fatigue critical point in the group studs.

ANALYSIS ON EFFECT OF PLATE SPACING ON SHEAR STIFFNESS OF PERFOBOND CONNECTORS

In order to discuss the reasonable plate spacing of perfobond connector, the influence of plate spacing on the shear stiffness of perfobond connector is analyzed through the push-out model test and based on the theory of elastic foundation beam. The calculation formula for perfobond shear stiffness is proposed, which accounts for the influence of plate spacing. Research results indicate that the plate spacing has little effect on shear capacity and peak slip of perfobond connector but changes the shear stiffness. Shear stiffness approximately linearly increases as the plate spacing increases, gradually approaching the single plate shear stiffness. The main influence factor for the shear stiffness of perfobond connector is the spacing-diameter ratio, which is suggested to be no less than 3.3 when multi perfobonds are arranged in parallel.

FEM analysis on failure development of group studs shear connector under effects of concrete strength and stud dimension

Group studs, arranging studs in group, has been applied as shear connectors in steel and concrete composite structures for over 50years. Concrete strength and stud dimension are the crucial factors affecting the failure appearance of shear studs in push-out test, which mainly consists of stud shear fracture, stud bending deformation and local concrete crush. Since the detailed failure development has rarely been concerned, a parametrical push-out FEM analysis with damage plasticity models on failure development of group studs with effects of concrete strength and stud dimension was executed. In this study, concrete compressive strength of 30MPa, 40MPa and 50MPa, shank diameters including 13mm, 16mm, 19mm and 22mm and stud heights including 80mm and 100mm were the parameters. In general, it was found that when under effect of concrete strength, shear stiffness of stud with large shank diameter performed more stable while its shear strength may be influenced more apparently. Meanwhile, the analyzed concrete damage, stiffness degradation and ultimate deformation of stud were discussed as well. The failure development of push-out model was reflected by the development of equivalent stud bending arm in terms of shear transfer between steel and concrete through studs, which experienced three steps due to the degradations of concrete and stud modulus. It also shows that models with lower concrete compressive strength or more flexible stud in combination with high concrete strength can lead to relatively obvious stud bending deformation.

Significant effect of a carbon layer coating on interfacial bond strength between bone and Ti implant

We investigated the degree of osseointegration in carbon-coated oxygen-diffused titanium implants (C-ODTi) by means of biomechanical tests of the femoral bones of rabbits. C-ODTi possesses interstitial oxygen atoms into the host titanium lattice and an upper nanometric surface layer of anatase-TiO 2 covered with 20 nm carbon layer. Interface shear strength was determined by using a transcortical push-out model at 4, 12 and 24 weeks after implantation. Implants with different surfaces were prepared, including a carbon coating and an abrasion treatment. There was a significant improvement in the bone-bonding shear strength for the C-ODTi. The highest shear strength values were observed in the C-ODTi group at 24 weeks and differed significantly from those of the control group at the same experimental time ( p < 0.05). After the in vivo evaluation it was concluded that the coating of a carbon layer on the surface of titanium implant was effective for improving the biocompatibility of titanium, which was evidenced by the superior interface shear strength.

On the mechanical stability of porous coated press fit titanium implants: A finite element study of a pushout test

Pushout tests can be used to estimate the shear strength of the bone implant interface. Numerous such experimental studies have been published in the literature. Despite this researchers are still some way off with respect to the development of accurate numerical models to simulate implant stability.In the present work a specific experimental pushout study from the literature was simulated using two different bones implant interface models. The implant was a porous coated Ti–6Al–4V retrieved 4 weeks postoperatively from a dog model. The purpose was to find out which of the interface models could replicate the experimental results using physically meaningful input parameters.The results showed that a model based on partial bone ingrowth (ingrowth stability) is superior to an interface model based on friction and prestressing due to press fit (initial stability).Even though the present study is limited to a single experimental setup, the authors suggest that the presented methodology can be used to investigate implant stability from other experimental pushout models. This would eventually enhance the much needed understanding of the mechanical response of the bone implant interface and help to quantify how implant stability evolves with time.

Titanium metals form direct bonding to bone after alkali and heat treatments

In this article we evaluated the bone-bonding strengths of titanium and titanium alloy implants with and without alkali and heat treatments using the conventional canine femur push-out model. Four kinds of smooth cylindrical implants, made of pure titanium or three titanium alloys, were prepared with and without alkali and heat treatments. The implants were inserted hemitranscortically into canine femora. The bone-bonding shear strengths of the implants were measured using push-out test. At 4 weeks all types of the alkali- and heat-treated implants showed significantly higher bonding strength (2.4–4.5 MPa) than their untreated counterparts (0.3–0.6 MPa). At 12 weeks the bonding strengths of the treated implants showed no further increase, while those of the untreated implants had increased to 0.6–1.2 MPa. Histologically, alkali- and heat-treated implants showed direct bonding to bony tissue without intervening fibrous tissue. On the other hand, untreated implants usually had intervening fibrous tissue at the interface between bone and the implant. The early and strong bonding to bone of alkali- and heat-treated titanium and its alloys without intervening fibrous tissue may be useful in establishing cementless stable fixation of orthopedic implants.

An energy-based analytical push-out model applied to characterise the interfacial properties of knitted glass fibre reinforced PET

Abstract In this study, the interfacial properties of weft-knitted glass fibre (GF)-polyethylene terephthalate (PET) composites were examined. On thin polished cut-outs of knitted GF/PET composite parts, push-out experiments were carried out at different temperatures using a push-out device set up in a SEM. Load–displacement curves were digitally recorded. FEM results suggested that crack initiation was located at or near the top of the free specimen surface. To interpret the load–displacement curves from the push-out experiments a new energy-based model was proposed. The model follows the principle of minimal energy and includes the effects of friction, Poisson expansion of the fibre, and energy release of the debonded part of the fibre. Crack progression was calculated applying the concept of interfacial surface fracture energy. With the proposed analytical model, the interfacial properties of GF/PET were extracted. The model is compared with existing approaches.

Control of Interfacial Properties through Fiber Coatings: Monazite Coatings in Oxide–Oxide Composites

Fiber pushout tests were used to quantify the effects of fiber coating thickness on the mechanical properties of two model composite systems: a monazite‐coated (LaPO4‐coated) alumina (Al2O3) fiber in an Al2O3 matrix and a LaPO4‐coated yttrium aluminum garnet (YAG) fiber in an Al2O3 matrix. Interface properties were quantified using the Liang and Hutchinson (LH) pushout model and mechanistically rationalized by considering the change in residual thermal stresses with changes in the coating thickness. Measures of the pure Mode II interfacial fracture energy, the coefficient of friction, and a radial clamping pressure are extracted by fitting the LH equations to the experimental results. Using the approach that has been developed herein, a methodology is available for measuring the interfacial properties, predicting the effect of coating thickness, and selecting the coating thickness to

Unified HBT base push-out and base-collector capacitance model

The presence of electron space-charge in the collector region of a transistor has the effect of offsetting the collector doping thereby giving a reduced effective doping concentration. This effect can modify the base-collector junction capacitance and for high current densities will give rise to base push-out. This paper describes the implementation of a unified junction capacitance and push-out model for the microwave HBT biased in the forward active mode. The threshold functions for pushout and full collector depletion are given and their significance for device and circuit design is discussed. An approximate description of the effect of pushout on the HBT forward time constant is described which accounts for the substantially increased diffusion constant in the pushout region.

Analyses of fiber push-out tests performed on Nicalon/SiC composites with tailored interfaces

The interfacial properties of Nicalon fiber-reinforced SiC composites with tailored (i.e. weak or strong) interfaces are characterized using single-fiber push-out tests. A simple analysis is proposed to include the surface roughness of the fiber in the push-out model. Specifically, the roughness effect is characterized by the difference between the fiber push-out stress and the fiber reseating stress, which is obtained from fiber push-back tests. A method is developed to analyze the loading stress vs fiber-end displacement relation (i.e. the push-out curve) during the push-out process to evaluate the interfacial properties. The push-out curve for composites with weak fiber bonding can readily be analyzed by the existing push-out model incorporated with the roughness effect. However, premature catastrophic debonding at the interface is required to interpret the push-out curves for composites with strong fiber bonding.

Analyses of fibre push-out test based on the fracture mechanics approach

Theoretical analyses based on the concept of fracture mechanics have been developed to evaluate the interfacial properties of ceramic matrix composites in single fibre push-out tests. Two different fibre push-out models, i.e. single fibre-matrix model and three-cylinder model, were presented for different specimen geometries. The interfacial debonding and fibre push-out stresses were analyzed similar to the fibre pull-out test ( Zhou et al., J. Mater. Sci. 27, 3155–3166 and 29, 5541–5550). In the three-cylinder model, the push-out of a single fibre in a specimen with multiple fibres was treated as a three-cylinder composite in which a fibre is located at the centre of a coaxial cylindrical shell of the matrix matrerial which in turn is surrounded by a transversely isotropic elastic material with elastic properties of the bulk composite. The radius of the matrix cylinder in this case is related to the volume fraction of the fibre which significantly affects the behaviour of interfacial debonding and fibre push-out. A simple methodology is presented on the basis of these analyses to determine the interfacial properties, including interfacial fracture toughness G ic, residual clamping stress q 0 and coefficient of interfacial friction μ, from the experimental results of maximum debond stress σ d ∗ (or initial debond stress σ d 0) and initial frictional push-out stress σ fr measured in a fibre push-out test. The effects of the fibre volume fraction, the transversely isotropic property and the Poisson expansion of the fibre are all considered in the analyses.

Analysis of Fiber Frictional Sliding in Fiber Bundle Pushout Test

A simple theoretical model is developed to analyze the fiber frictional sliding resistance in a fiber bundle pushout test. The effect of the radial constraint imposed by the neighboring fibers on the stress transfer and frictional pushout stress is included in this analysis. Comparisons of theoretical results of this study and those of two existing fiber pushout models (i.e., single‐fiber pushout and three–cylinder) are also presented. For SiC–RBSN and SiC–glass composites with short embedded fiber lengths less than 1 mm, there is little difference between all these models. However, for larger embedded fiber lengths, the present model gives the highest frictional pushout stress caused by the more realistic radial constraint condition used in the analysis.

Ｂｉｏｉｎｅｒｔセラミックスの生体内固着力の検討

We have previously demonstrated that there was no significant difference between the affinity of bone to bionert ceramics and stainless steel in a histological study. In this study, the bone-implant interface shear strength of alumina ceramics (Al2O3), zirconia ceramics (ZrO2), stainless steel (SUS316L) and sintered hydroxyapatite (HA) were compared in 13 dogs using a transcortical push-out model of the femur 4 and 12 weeks after implantation. The interface shear strength of HA was significantly greater than that of alumina ceramics, zirconia ceramics and stainless steel (P<0.001). There was no significant difference between bioinert ceramics and stainless steel. Young's modulus of stainless steel is higher than that of cortical bone, but Young's modulus of bioinert ceramics is much higher than both cortical bone and stainless steel. With the stimulus of weight-bearing, the shearing stress along the interface becomes greater as the difference between Young's modulus of the implant and that of bone increases, and functional compatibility is believed to decline. Consequently, bioinert ceramics offer little advantage in terms of biomechanical compatibility to bone over metal alloys. We recommend a review of the use of bioinert ceramics at the bone-implant interface in orthopaedic prostheses.

Micromechanical characterisation of fibre/matrix interfaces

Theoretical analyses for the single fibre pull-out and push-out models under monotonic loading are given which are based on a shear-lag analysis in a fracture mechanics approach considering non-constant friction at the debonded interface as a result of fibre Poisson contraction (or expansion). The solutions allow the determination of typical fibre/matrix interfacial properties such as the interfacial fracture toughness, G ic, the coefficient of friction, μ, and the residual clamping stress, q 0. Under cyclic loading the interfacial properties are expected to degrade as a result of repetitive abrasion, and a power law function is assumed between μ and the number of elapsed cycles, N. However, G ic is assumed to be unaffected and a fracture mechanics based debond criterion is derived for the relationship between the external applied stress, the debond length and the reduced friction coefficient for both fibre pull-out and fibre push-out. In addition, the relative displacements between the free fibre end and the matrix top are obtained for cyclic fatigue when the fibre is loaded and unloaded. A relationship obtained for the protrusion (or intrusion) length in fibre pull-out (or push-out) experiments allows the severity of the interface frictional degradation to be evaluated and characterised. Similarities and differences in the frictional degradation behaviour between fibre pull-out and push-out are also identified.

Bone-implant interface mechanics of in vivo bio-inert ceramics

We have previously demonstrated that there was no significant difference between the affinity of bone to bio-inert ceramics and stainless steel in a histological study. In this study, the bone-implant interface shear strength of alumina ceramics (AI 2O 3), zirconia ceramics (ZrO 2), stainless steel (SUS316L) and sintered hydroxyapatite (HA) were compared in 19 dogs using a transcortical push-out model of the femur 4 and 12 wk after implantation. The interface shear strength of HA was significantly greater than that of alumina ceramics, zirconia ceramics and stainless steel ( P < 0.001). There was no significant difference between bio-inert ceramics and stainless steel.

A physically based base pushout model for submicrometer BJTs in the presence of velocity overshoot

By using a two-dimensional relaxation time approximation device simulator, base pushout phenomena for submicrometer bipolar junction transistors (BJTs) are analyzed. From the numerical analysis, it was clarified that, under the base pushout condition, the electron velocity exceeds the saturation velocity in most of the epi-collector region. Considering this velocity overshoot effect with two-dimensional carrier behavior, a base pushout model was developed. This model is applicable to the BJT equivalent circuit model. The model utility was verified for a 0.8 mu m emitter-width BIT, and excellent agreement with measured I-V characteristics was obtained over wide injection conditions. Scaling effects on the velocity overshoot are also calculated, based on the constant current scaling. It is shown that the base pushout is suppressed due to the increased velocity overshoot level as the device sizes are scaled down. >

Experimental Coating Defects in Hydroxylapatite-Coated Implants

Defects in hydroxyapatite (HA)-coated metallic implant systems, including cracks, flakes, or scratches, may occur at the time of surgery or in time because of in vivo loading. Such defects may affect the bone-implant interface response because of increased local metallic corrosion and ion release. Using a canine transcortical push-out model, the interface mechanics and histology of HA-coated titanium and cobalt-chromium-molybdenum alloy implants with and without coating defects were evaluated. The coating defects extended through the HA material to the underlying metallic substrate. Interface mechanical testing and undecalcified histologic techniques were used to evaluate differences in interface response at three, five, six, ten, 12, and 32 weeks postimplantation. There were no statistically significant differences between the HA-coated implants with and without defects for either interface shear strength or stiffness; however, both HA-coated implant types developed significantly greater interface strength and stiffness when compared to uncoated metallic implants. Histologically, in all areas away from the defect, a progression to nearly complete mineralization of osseous tissue directly onto the HA-coated surface was observed with no interpositional fibrous tissue layer. At early time periods (up to six weeks) in the area of the coating defect, bone apposition and mineralization appeared to stop at the edge of the HA coating. At later time periods (greater than ten weeks), the area of the defect was filled with mineralized osseous tissue in approximately one-half of the specimens. A thin fibrous interpositional layer was observed at the interface of the exposed metal substrate.