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1.
In Steel–Concrete–Steel (SCS) sandwich structure, mechanical shear connectors are commonly used to transfer longitudinal shear forces across the steel–concrete interface. In this paper, novel shear connectors such as J-hook and cable shear connectors are proposed and their performance to achieve composite strength of SCS sandwich structures is investigated. The use of these connectors together with ultra-lightweight cement composite core reduces the overall weight of SCS sandwich system making it suitable for the construction of marine and offshore structures. Static tests were carried out on SCS sandwich beams with J-hook, cable shear connectors and headed studs. Their ultimate strengths were reported and their respective failure modes were discussed. An analytical method to predict the ultimate strength of the Steel–Concrete–Steel sandwich beams with various types of shear connectors was developed and its accuracy was ascertained by comparing with the test results. Deign recommendations are made on minimum connector spacing to prevent shear cracking of concrete core and local buckling of face plates. 相似文献
2.
Bonding between the adherents represents a key point when dealing with the reinforcement of concrete structures by using FRPs. Bonding depends on mechanical and physical properties of concrete, composite and adhesive as well as on the surface treatment of the concrete substrate. A very important topic for civil engineering applications is related to the durability of the bond in harsh environments. In the present paper some specimens were first subjected to freeze–thaw cycles and then experimental debonding tests were performed in order to investigate the effects of the bonding length and environmental conditions. First, the effects of environmental conditions on bond strength is discussed. Finally, the experimental data are compared to the design formulae proposed by the Italian Recommendations CNR DT200/2004 and critical considerations are presented. 相似文献
3.
The paper is focused on shear bond strength–masonry compressive strength relationships and the influence of bond strength
on stress–strain characteristics of masonry using soil–cement blocks and cement–lime mortar. Methods of enhancing shear bond
strength of masonry couplets without altering the strength and modulus of masonry unit and the mortar are discussed in detail.
Application of surface coatings and manipulation of surface texture of the masonry unit resulted in 3–4 times increase in
shear bond strength. After adopting various bond enhancing techniques masonry prism strength and stress–strain relations were
obtained for the three cases of masonry unit modulus to mortar modulus ratio of one, less than one and greater than one. Major
conclusions of this extensive experimental study are: (1) when the masonry unit modulus is less than that of the mortar, masonry
compressive strength increases as the bond strength increases and the relationship between masonry compressive strength and
the bond strength is linear and (2) shear bond strength influences modulus of masonry depending upon relative stiffness of
the masonry unit and mortar. 相似文献
4.
Ishihara S Goshima T Kanekasu K McEvily AJ 《Journal of materials science. Materials in medicine》2002,13(5):449-455
Four-point bending static and fatigue tests were carried out on bone–cement bonds. The effects of the pressurization and the washing of the bone joint face on the bond strength were investigated. The results are summarized as follows. When the bond surface of cancellous bone is washed prior to the application of the bone cement, both the static and fatigue strengths of the bond are increased relative to the corresponding properties of unwashed bone–cement bonds. From observations of bone–cement interfaces as well as the fracture surfaces of bone–cement specimens, it has been determined that bone cement was able to infiltrate into fine holes present in washed cancellous bone. However, such infiltration occurred to a much lesser degree in the case of unwashed cancellous bone. Increasing the molding pressure during the time of cement application to the bone from 39200 to 117600 Pa had a beneficial effect on the bending strength and fatigue properties, particularly in the case of washed bone cement specimens. An increase in molding pressure also resulted in a reduction in the amount of scatter in test results. 相似文献
5.
J. Q. Xue L. T. Dang J. Zhang C. B. Tang Y. Gao B. Gao 《Materials Science & Technology》2015,31(2):248-253
AbstractCasting of titanium can be successfully used in prosthodontic applications, but it demands special machines and protection gas to avoid oxidation of the metal. The aims of this study are to investigate the bond compatibility between porcelain and titanium using three-point bending, oxide adherence and thermal expansion tests, and to compare the results with those of a conventional titanium–porcelain system. Titanium alloy surfaces were modified with Nb, YG8 and silicon electrode by electrospark surface modification process. The effect of electrospark surface depositing (ESD) layers on bond strength of titanium to porcelain was evaluated comparatively. Some reasons about bond strength of titanium to porcelain were discussed. Results indicate that ESD modified layer prepared in atmosphere using Si electrode can obtain the strongest bonding to porcelain. The ESD modified layer show metallurgical bond to Ti substrate. In addition, the facts that rough surface can help to improve physic bond, similar nature can also help to chemical link and compact ESD layer represent good high temperature oxidation resistance are the reasons that enhance good bond strength of titanium to porcelain. 相似文献
6.
B. Henriques D. Soares F.S. Silva 《Materials science & engineering. C, Materials for biological applications》2012,32(8):2374-2380
The purpose of this study was to evaluate the effect of preoxidation cycle on the shear bond strength (SBS) of CoCrMoSi alloy–porcelain dental composites. The porcelain was fired onto three types of metal surfaces: non-preoxidized, preoxidized and, preoxidized followed by grinding. The bond strength of metal–porcelain composites was investigated by the means of a shear test. The metal–ceramic interfaces and the fractured surfaces were analyzed using Optical Microscopy, Stereomicroscopy and SEM/EDS. Data was analyzed with Shapiro–Wilk test to test the assumption of normality. The t-test was used to compare shear bond strength results (p < 0.05). The analysis of the three types of surfaces was performed prior to porcelain firing. It was also performed a complementary analysis of an alumina-blasted preoxidized CoCrMoSi surface. The greater metal–porcelain adhesion was obtained for non-preoxidized specimens.Non-preoxidized specimens showed significantly (p < 0.05) higher shear bond strength than preoxidized/ground specimens, 115.5 ± 7.5 MPa and 74.8 ± 8.5 MPa, respectively. Porcelain showed no adhesion to preoxidized specimens. All preoxidized specimens exhibited adhesive failure type while non-preoxidized presented both adhesive and mixed failure types. Preoxidation heat treatment revealed a detrimental effect on the adhesion of CoCrMoSi–porcelain composites for dental restorations. Hence, in order to enhance CoCrMoSi–porcelain adhesion, the preoxidation heat treatment conditions, as performed in this study, should not be performed. 相似文献
7.
Behavior of rectangular concrete columns confined with FRP composites depends on several parameters, including unconfined concrete strength, confinement level, aspect ratio of cross-section (defined as the depth/width of the cross-section), and the sharpness of the section corners. For modeling the cyclic stress–strain behavior of FRP-confined rectangular concrete columns, effect of column parameters on the cyclic behavior of these columns should be examined properly. In this paper, effects of unconfined concrete strength, confinement level and the aspect ratio of cross-section are studied. The test database includes 10 prisms from recent study of authors and 18 prisms from a new experiment. Results of tests show that some aspects of cyclic behavior of FRP-confined concrete prisms such as envelope curve and stress deterioration are unaffected by the considered parameters. Results also indicate that the plastic strain decreases as the unconfined concrete strength increases, but it is independent of the aspect ratio and the confinement level. While the reloading path in all specimens was almost linear, the unloading path was highly nonlinear and was affected by unconfined concrete strength. 相似文献
8.
Saturated surface-dry condition of fine aggregate has been well defined in mortar and concrete production as the dry mass
percentage moisture content where aggregate particles are saturated. However in soil–cement concrete construction, no mix
design based on the saturated surface-dry condition of soil was attempted partly because the control of soil moisture on site
is difficult. We have proposed the definition and testing methods of the saturated surface-dry condition of soil in the previous
papers. In this paper, we introduce the concept of effective unit water to the soil–cement concrete mix design and propose
a mix design method for soil-sand-cement systems. Strength and density of the soil–cement concretes were determined and discussed.
A number of mixes were proportioned with accurate control of composition (C/W, soil/sand ratio, free water, etc.) and consistency. It was found that strength can be determined by C/W for a wide variety of clayey soils in various soil/sand ratios except for a soil with very high content of organic material.
A set of nomograms for C/W versus strength and soil/sand versus strength were presented for future proportioning. 相似文献
9.
Jiang Wu Jian Zhou Wen Zhao Bo Gao 《Materials science & engineering. C, Materials for biological applications》2013,33(1):140-144
The purpose of this study was to compare the bonding characteristics of titanium porcelain Duceratin bonded to Ti–24Nb–4Zr–7.9Sn (TNZS) alloy and commercial pure titanium (cp Ti). The bond strengths between porcelain and TNZS were tested by a three-point flexural device. The same tests for the cp Ti were used as for the control. Coefficient of thermal expansion (CTE) of TNZS was evaluated with a push-rod dilatometer. Interfacial characterization was carried out by X-ray energy-dispersive spectrometry (EDS) analysis operating in line scan mode. Additionally, microstructure characterizations of TNZS and cp Ti after debonding fracture were analyzed by scanning electron microscope (SEM) and EDS. The porcelain bond strength of TNZS alloy was 31.51 MPa, showing a significant increase relatively to that of cp Ti (23.89 MPa) (P < 0.05). Mean CTE values of TNZS alloy was 9.51 × 10? 6/°C exceeding the porcelain by 0.81 × 10? 6/°C, attesting to a better mechanical performance. Interfacial characterization showed the mutual diffusion of Ti, Si, O and Sn along the TNZS–ceramic interface. Both SEM and EDS results revealed that fracture modes of TNZS specimens exhibited a mixed mode of cohesive and adhesive failures. The results demonstrated that TNZS could be a good alternative for the metal–ceramic restoration in the future. 相似文献
10.
This paper will focus on the study of reinforced concrete beams stored in a chloride environment for a period of 14–23 years
under service loading. According to the experimental results, a Serviceability Limit State (SLS) criteria is proposed based
on an excessive steel–concrete bond reduction. Corrosion of reinforcement in chloride environment leads to a specific local
steel cross-section loss as well as a steel–concrete bond loss. Experimental results have shown that, in the first stage of
corrosion propagation period, the deflection is more sensitive to chloride-induced corrosion than the ultimate capacity due
to the effect of the tension steel–concrete bond loss even if both are correlated. Given this high sensibility of the bending
stiffness to corrosion pitting attacks, it appears that a Serviceability Limit State (SLS) criteria based on excessive deflection
of structural members is an adequate factor for SLS assessment. Later in corrosion propagation period, when the bond is already
significantly reduced, only the ultimate capacity is affected by the steel cross-section loss. This does not affect the serviceability,
because pitting attacks are very localised with an insignificant influence on the global deflection. Then, once the steel–concrete
bond is lost in critical parts of the beams (high bending moment areas), pitting corrosion propagation does not affect anymore
serviceability (stiffness reduction, bending or corrosion cracks patterns) but still leads to an ultimate capacity reduction,
which is not acceptable. As a result, excessive steel–concrete debonding can be considered as the SLS criteria. 相似文献
11.
《Composites Part A》2001,32(3-4):435-443
Three techniques of bond strength determination in micromechanical tests—fibre strain profile analysis by means of Raman spectroscopy, “kink” force determination in a traditional pull-out test, and crack length monitoring in a microbond test—were used for investigation of interfacial debonding in epoxy–glass fibre and epoxy–aramid fibre systems. Crack propagation was characterised by local interfacial parameters—critical energy release rate, Gic, and ultimate interfacial shear strength (IFSS), τult. The comparison of the results showed good agreement both between different techniques and between stress-based and energy-based failure criteria. Sizing of glass fibres caused more pronounced variations in the IFSS than for aramid fibres due to different interfacial failure patterns. The strength of “real” epoxy–glass composites with sized and unsized fibres correlates well with the bond strength determined from the micromechanical tests. 相似文献
12.
Bond–slip relationship of externally-bonded (EB) fiber reinforced polymer (FRP) joints can be determined by either directly or indirectly from a pull-off test. The indirect analytical method is gaining popularity and has been recommended in recent literature because of the more consistent and accurate results it yields. To date, loaded end slip vs applied load curve is used for indirect identification of the bond–slip relationship, ignoring the free end slip. This work shows that ignoring free end slip may result in significant errors in measuring the bond–slip relationship. The analytical method is used in this work to derive closed form solutions for FRP strain, interface slips, and bond strength of EB-FRP joints. The analytical solutions are validated by experimental results. Using the analytical solution, it is clearly shown in the paper that free end slip affects results and should be considered in deriving bond–slip relationship of EB-FRP joints, especially when bond length is short. 相似文献
13.
《Materials Science & Technology》2013,29(1):87-92
AbstractA unidirectional SiC fibre reinforced pure aluminium composite was fabricated by the hot press method. Tensile testing of the SiC–Al was carried out to determine composite and interfacial shear strengths. A Monte Carlo procedure based on the elastic–plastic finite element method, involving the interfacial layer around the fibres, was constructed to simulate the tensile testing and to calculate the strength and Weibull parameters for the SiC–Al composite. The effect of the interfacial shear strength on the composite strength and its reliability is discussed. The results show that the composite strength and the Weibull shape parameter increase with increasing interfacial shear strength. The contribution of the interfacial shear strength to the composite strength and reliability is efficient when the interfacial shear strength is lower than the matrix shear strength. It is concluded that both composite strength and reliability are closely related to the fibre fracture process. 相似文献
14.
Krzysztof J. Leśnicki Jin-Yeon Kim Kimberly E. Kurtis Laurence J. Jacobs 《Materials and Structures》2013,46(3):497-509
A newly developed nondestructive evaluation technique, Nonlinear Impact Resonance Acoustic Spectroscopy (NIRAS), is applied to concrete specimens in an ongoing assessment of aggregate alkali reactivity during standard concrete prism testing. NIRAS measures the nonlinearity in a specimen caused by the inception and growth of microcracks throughout the sample and debonding at the aggregate/cement interface. NIRAS is used to exploit the nonlinear effect of excitation amplitude dependent resonance frequency changes, which are related to nonlinearity measurements of concrete samples cast with aggregates of varying reactivity. To relate microstructural changes to changes in nonlinearity and expansion, sample characterization is performed with uranyl-acetate staining. The results demonstrate the utility of NIRAS for not only assessing the potential for ASR under standardized test conditions, but for more general damage characterization in concrete and assessment of “job mixtures.” NIRAS can distinguish reactive from nonreactive aggregates without ambiguity, as supported by sample characterization results. 相似文献
15.
The problem of debonding of FRP plates glued over a concrete element is studied making use of boundary integral equations. Mode II cohesive crack model is adopted for the interface, whereas linear elasticity is used for the two materials outside the process zone. Symmetric Galerkin boundary element method is used, adopting the arc-length technique to follow the equilibrium path beyond its critical point. It is shown that, due to the presence of a softening branch in shear stress-slip law, the behavior of a specimen undergoing debonding may be strongly non-linear, and is associated with a very brittle failure mechanism. For bond lengths longer than minimum anchorage length, a snap-back branch typically occurs after the attainment of the maximum force. Two different test setups have been numerically simulated and results in good agreement with experimental tests are found. 相似文献
16.
Timber–concrete composite beams and slabs require interlayer connectors, which provide composite action in the cross-section.
A range of mechanical connectors is available on the market with an extensive variety of stiffness and strength properties,
which are fundamental design parameters for the composite structure. Another crucial parameter is the cost of the connector,
including the labour cost, that if too high may prevent the use of the composite system. In order to reduce the construction
cost and make timber–concrete structures more widespread on the market, it is believed that a high degree of prefabrication
should be achieved. For a simple and cost effective construction process, the use of “dry” connections, which do not require
the pouring and curing of concrete on site, may represent a possible solution. This paper reports the outcomes of an experimental
programme aimed to investigate a number of different mechanical “dry–dry” connectors previously embedded into a prefabricated
concrete slab. Direct shear tests on small blocks made of a glulam segment connected with a prefabricated concrete slab were
performed. The shear force-relative slip relationships were measured and all the relevant mechanical properties such as slip
moduli and shear strengths were calculated. It was found that some of the new developed connection systems for prefabricated
concrete slab can perform as satisfactorily as those for cast-in-situ slabs, with the additional benefit of being relatively
inexpensive. 相似文献
17.
Ryoichi Monzen Takasumi Hosoda Yusaku Takagawa Chihiro Watanabe 《Journal of Materials Science》2011,46(12):4284-4289
The effects of addition of 0.01 and 0.03 wt% Mg on the bend formability and strength of a Cu–1.8 wt% Be–0.21 wt% Co alloy
aged at 320 °C for 30 min have been investigated metallographically. The addition of Mg to the Cu–Be–Co alloy enhances the
bend formability and strength of the alloy. The enhancement of strength is caused by the increase in volume fraction of
g\textI¢ \gamma_{\text{I}}^{\prime } precipitates in the Cu matrix. In bending of the alloys with and without 0.01 and 0.03 wt% Mg, a number of micro necks first
arise along grain boundaries, and part of them grows, resulting in surface wrinkles, which finally lead to surface cracking.
The cracking is initiated from voids formed by destruction of bar-like γ precipitates in discontinuous precipitation (DP)
cells and propagates along grain boundaries. The addition of Mg decreases the width of DP cells, resulting in better bend
formability. This arises because smaller stress concentration due to less inhomogeneous deformation develops in cells and,
as a result, destruction of the γ precipitates in cells occurs less easily as the cell width decreases. 相似文献
18.
The aim of this study is to investigate the role of 0–2 mm fine aggregate on the compressive and splitting tensile strengths of recycled concrete aggregate (RCA) concrete with normal and high strengths. Normal coarse and fine aggregates were substituted with the same grading of RCAs in two normal and high strength concrete mixtures. In addition, to keep the same slump value for all mixes, additional water or superplasticizer were used in the RCA concretes. The compressive and splitting tensile strengths were measured at 3, 7 and 28 days. Test results show that coarse and fine RCAs, which were achieved from a parent concrete with 30 MPa compressive strength, have about 11.5 and 3.5 times higher water absorption than normal coarse and fine aggregates, respectively. The density of RCAs was about 20% less than normal aggregates, and, hence, the density of RCA concrete was about 8–13.5% less than normal aggregate concrete. The use of RCA instead of normal aggregates reduced the compressive and splitting tensile strengths in both normal and high strength concrete. The reduction in the splitting tensile strength was more pronounced than for the compressive strength. However, both strengths could be improved by incorporating silica fume and/or normal fine aggregates of 0–2 mm size in the RCA concrete mixture. The positive effect of the contribution of normal sand of 0–2 mm in RCA concrete is more pronounced in the compressive strength of a normal strength concrete and in the splitting tensile strength of high strength concrete. In addition, some equation predictions of the splitting tensile strength from compressive strength are recommended for both normal and RCA concretes. 相似文献
19.
Steel–concrete–steel (SCS) sandwich panels are an effective means for protecting personnel and infrastructure facilities from the effects of external blast and high-speed vehicle impact. In conventional SCS construction, the external steel plates are connected to the concrete infill by welded shear stud connectors. This paper describes a programme of research in which the non-composite SCS panels with axially restrained connections were studied experimentally and numerically. High fidelity finite element models for axially restrained steel–concrete–steel panels subjected to impact loading conditions were developed using LS-DYNA. The simulation results were validated against the dynamic testing experimental results. The numerical models were able to predict the initial flexural response of the panels followed by the tensile membrane resistance at large deformation. It was found that the strain rate effects of the materials and the concrete material model could have significant effect on the numerically predicted flexural strength and tensile membrane resistance of the panels. 相似文献
20.
《Materials Science & Technology》2013,29(11):1331-1334
AbstractSintered Al2O3 was joined to Ni–Cr steel by the active metal brazing route with Ag–Cu–Zr brazing alloys containing Sn or Al. A single ZrO2 layer with a monoclinic structure was formed at the Al2O3 /brazement interface by the migration of Zr in the molten brazing alloy to the Al2O3 surface, followed by a redox reaction between the Al2O3 and Zr. The remainder of the brazement formed a Cu–Ag eutectic alloy. Precipitates CuZr2 and Cu–Zr–Al were formed in the brazements of the Ni–Cr steel/ Al2O3 joints brazed with Ag–Cu–Zr alloys and Al containing Ag–Cu–Zr alloys, respectively. On the other hand, no precipitates were formed in the brazement of the Ni–Cr steel/Al2O3 joints brazed with Sn containing Ag–Cu–Zr alloys. The Ni–Cr steel/ Al2O3 joints brazed with Sn containing Ag–Cu–Zr alloys showed much higher fracture shear strengths than those brazed with Ag–Cu–Zr alloys or Al containing Ag–Cu–Zr alloys. 相似文献