Composite Strips Research Articles

Effect of particle size on microstructure and mechanical properties of composites produced by ARB process

In the present work, Al/10 vol.% SiC metal matrix composite (MMC) was manufactured by accumulative roll bonding (ARB) process. The silicon carbide particles with two various particle sizes of 40 and 2 μm were used. Effect of particle size on microstructure (by scanning electron microscopy) and mechanical properties (tensile strength and elongation) at various ARB cycles was investigated. It was found that the microstructural evolution in MMC with 40 μm particle size was more salient compared to the MMCs with 2 μm particle size. Also, the composite strip with 40 μm particle size became uniform with high bonding quality and without any porosity sooner than the strip of 2 μm particle size. Moreover, when the number of cycles was increased, the tensile strength for both samples was improved. The tensile strength of the composite strip with 40 μm particle size was more than the composite strip with 2 μm up to the seventh cycle. By increasing the number of cycles after the seventh cycle, the value of tensile strength of MMC with 40 μm particle size became saturated and then decreased, and its tensile strength became less than that of the composite with 2 μm particle size for the ninth and eleventh cycles. Up to the seventh cycle, when the number of ARB cycles was increased, the elongation of composite strips was decreased, but after the ninth cycle, the tensile elongation for both samples was improved.

Investigation of the temperature field induced in the process of friction of a composite pad and a homogeneous disc

The analytical model for the determination of transient temperature field and heat fluxes in friction elements of brakes (pad/disc) is presented. It is assumed that one friction element is composed of a multi-layer composite strip, and the second element is a homogeneous semi-space. The solution to a non-stationary thermal problem of friction is obtained for a tribosystem with heat generation on a surface of contact and convective heat exchange with an environment on outer surface of a strip. The influences of composite parameters, for example, reinforcement fraction in the cross-section of periodic cells and the ratio of the conductivities of matrix and fibers, on the maximal temperature are studied.

Roll Casting of Al-SiC<sub>p</sub> Composite Strip

Roll casting of Al-SiCp composite alloy strip was tried using a vertical type high speed twin roll caster equipped with mild steel rolls. The Al-20vol% SiCp and Al-30vol%SiCp alloy could be roll-cast to the strip. The casting speed was 30m/min. The thickness of as-cast strip was thinner than 2.5mm. The SiCp powder was dispersed uniformly at the thickness direction. The as-cast strip could be thin down to 1mm by the hot rolling and the cold rolling without broken.

Development of an innovative seismic strengthening technique for traditional load-bearing masonry walls

Traditional non-reinforced masonry walls are particularly prone to failure when subjected to out-of-plane loads and displacements caused by earthquakes. Moreover, singularities such as openings in facades may trigger local collapse, for either in-plane or out-of plane motion. Bearing in mind all the former limitations, STAP, with the scientific support of ICIST and LNEC, has been developing a reduced intrusiveness seismic strengthening methodology for traditional masonry structures. The technique consists in externally applying Glass Fibre Reinforced Polymer (GFRP) composite strips to one or both faces of walls. Connection between GFRP composite strips and masonry substrate is enhanced through specifically detailed anchorages or confinement connectors. This technique has been developed and studied through an extensive series of experimental tests, which are briefly reviewed. This paper focuses more deeply on the latest experimental program, aimed at the characterization of the masonry-GFRP composite interface behaviour. This testing program comprised 29 masonry specimens, strengthened with externally bonded GFRP composite strips with anchorages. The testing variables were the number and spacing of anchorages as well as the loading history type: monotonic or repeated. Results clearly show that the use of anchorages dramatically enhances bond behaviour and that its number and spacing have a significant effect on deformation capacity and a less pronounced effect on strength. Based on experimental evidence, this paper also provides a calculation model and ULS safety assessment procedure for out-of-plane strength of reinforced masonry walls. This calculation model leads to interaction curves on strengthened masonry walls subjected to compression and out-of-plane flexure.

Biomimetic flexible/compliant sensors for a soft-body lamprey-like robot

This paper focuses on the development of biomimetic sensory abilities for an undulatory soft-body lamprey-like robot, which has been designed to replicate the locomotion mechanisms of living lamprey in order to address useful applications wherever locomotion in unstructured environments is required. The compliant sensory elements are piezo-resistive and made from compliant material called a quantum tunneling composite by mixing micro/nano carbon black particles into a highly soft silicone rubber matrix. The relationship of the composite strip between piezo-resistivity and mechanical strain is investigated by a universal strain–stress tensiometer through resistivity monitoring. Increasing and decreasing resitivity both appears during elongation and retraction, suggesting that piezo-resistivity in the composite material is governed by both percolation theory and quantum tunneling effects. Dynamic tests on the bench shows that the compliant stretch receptor is able to follow the stimulations under fairly wide frequency ranges, exceeding initial estimations. In addition, the compliant artificial stretch receptor has enough sensitivity to detect the local actuations and the actions generated by neighboring actuators in the segmented robotic structure. Finally, the experiments on biomimetic cilia-based cupula receptor show that a low cost flexible/compliant biomimetic sensor is able to detect medium fluidic speeds ranging from 0.05 m/s to 0.6 m/s.

Static Analysis of Reinforced Concrete Beams Strengthened with CFRP Composites/ Analiza Statyczna Belek Zelbetowych Wzmocnionych Tasmami Kompozytowymi

Abstract This paper presents the possibility to apply numerical simulation in static analysis of reinforced concrete structure strengthened with carbon fibre reinforced polymer composite strips (CFRP). Reinforced concrete beams, with strengthening in form values CFRP made of carbon fibres and epoxy resin, featuring various width, as well as non-strengthened bent beams, were analysed. The simply supported beams arranged in a free support scheme were subjected to two concentrated forces within full range of loading (until collapse). The numerical analysis was performed through application of the Finite Elements Method (FEM), and the calculation model applied took into account the geometric and physical nonlinearity. The problem was solved by application of the quasi-static strategy method of calculations using ABAQUS software. While analysing the results, we focused on the run of changes in structure displacement and development of material damage, up to the point of destruction of the beam

Buckling-driven debonding in stiff block: compliant joint structural assemblies patched with composite materials

The initiation, growth, and stability of buckling driven debonding in structural assemblies of stiff blocks, compliant joints, and adhesively bonded composite layers are analytically investigated. The model is developed with focus on masonry walls externally strengthened with composite materials where static and, mainly, dynamic loads may induce compression in the strengthening layers triggering a buckling driven debonding near the joints. The model introduces the interfacial nonlinearity (debonding) through a cohesive interface approach. The geometrical nonlinearity is introduced through the kinematics of intermediate class of deformation (large deflections, moderate rotations, small strains), and the material nonlinearity of the masonry construction is introduced through the constitutive law for the mortar joints. A numerical study of the debonding process in strengthened masonry walls is presented. The study uses the periodicity of the wall for sub-structuring and examines configurations that include composite strips or sheets, strengthening on one face of the wall or on both faces, and compliant mortar materials. Emphasis is placed on the localized debonding near the joint, its stability characteristics, and the possibility to detect the debonding process before it reaches the point of instability.

A Resonant Vibrating Tactile Probe for Biomedical Applications Based on IPMC

In this paper, a vibrating tactile probe is presented. The probe exploits the dependence of its resonant frequency on the varying load and hence on the contacted material. This methodology allows the recognition of different materials by observing the electrical quantities involved in the probe dynamics. More specifically, two ionic polymer-metal composite (IPMC) strips are used, one as actuator and one as sensor, that work together for the recognition of materials. The actuator forces the system into resonant conditions that, as stated before, change with the mechanical properties of the contacted material. The output signal produced by the IPMC sensor contains the information required for the estimation of the contacting material. The sensing capabilities could be exploited in various biomedical applications, such as catheterism and surgical resection of tumors. The model and the experimental validation of the proposed probe are reported. For each material, different surveys were collected to estimate the uncertainty of the resonant frequency and hence to obtain the characteristic diagram of the device along with its uncertainty. The reported results show that the developed probe can be used to distinguish among different materials.

Unreinforced Concrete Masonry Walls Strengthened with CFRP Sheets and Strips under Pendulum Impact

Impact tests using drop-weight pendulum on nine 1.2-m-high full-scale concrete masonry block walls were conducted to investigate the out-of-plane impact behavior of unreinforced masonry (URM) walls externally strengthened with carbon-fiber-reinforced polymer (CFRP) composites. Three strengthening schemes on one side of the wall were studied: continuous unidirectional and continuous woven sheets, discrete strips in a vertical pattern, and discrete strips in orthogonal and diagonal patterns. All walls were vertically positioned resting on a knife-edge support with one face leaning against two steel rollers close to the upper and lower edges of the wall. The impact load was applied at the wall center through a drop-weight pendulum impact tester with various drop heights. Test results revealed that using composite laminates or strips could significantly improve the impact performance of URM walls. The wall strengthened with continuous woven sheets performed better than the one with unidirectional sheet. With ...

Failure characteristics of FRP-strengthened masonry walls under out-of-plane loads

The failure behavior of masonry walls strengthened with composite materials and subjected to out-of-plane loading up to failure is analytically and experimentally investigated. Emphasis is placed on realistically supported strengthened walls under conditions that restrict the elongation and allow the development of the arching action. A combined experimental–theoretical characterization of the behavior of the strengthened wall throughout the entire loading process and a quantification of their failure criteria are presented. The experimental phase includes loading to failure of a full-scale masonry wall strengthened with composite strips and a full-scale control specimen. A series of tests for the characterization of the mechanical properties of the materials and interfaces involved is also reported. In the theoretical phase, an enhanced analytical model that accounts for the behavior of the various materials, interfaces, and components under the entire spectrum of load levels is presented. The results and the theoretical–experimental comparison provide insight into the failure behavior of the strengthened wall and throw light on some of its unique failure mechanisms.

Roll Casting of Net Inserted Aluminum Alloy Strip

The net-inserted metal matrix composite strip could be cast by a twin roll caster at only one process. The caster for composite strip was assembled by combination of the open-top melt drag type and the downward melt drag type caster. The matrix was Al-12mass%Si, and inserted net was made from SUS304 stainless steel. The diameter of the wire of the net was 0.29 mm, and distance between the wires was 0.98 mm (#20). The roll speed was 30 m/min. The net was not reacted with the matrix, and there was not gap between the matrix and the net. The mechanical property of the net-inserted composite strip was affected by the direction of the wire of the net. When the angle of the wire against the tensile direction was 45 degrees, elongation of the composite became better than that of the matrix from 14% up to 23%. This reason was improvement of the local contraction of the composite strip. The net-inserted composite strip could be cold rolled. The reduction of the net was smaller than that of the strip. The reduction of the wire at rolling direction was larger than that of the wire at lateral direction.

Estimation of heat flux and temperature distributions in a composite strip and homogeneous foundation

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown time-dependent heat flux and temperature distributions for the system composed of a multi-layer composite strip and semi-infinite foundation, from the knowledge of temperature measurements taken within the strip. It is assumed that no prior information is available on the functional form of the unknown heat flux; hence the procedure is classified as the function estimation in inverse calculation. Results show that an excellent estimation on the time-dependent heat flux can be obtained for the test case considered in this study.

504 傾斜機能層が挿入された積層複合中空球の非定常熱弾性解析(GS-3 熱応力・熱弾性(1))

Functionally graded materials (FGMs) are inhomogeneous materials, in which the properties vary continuously from one surface to the other. Typically, these materials are made from a mixture of ceramic and metal. The characteristics of ceramic yield the high-temperature resistance due to their excellent and thermal property, but have a serious defect such as brittleness. The characteristics of metal, on the other hand, prevent fracture caused by stresses due to their mechanical strength. FGMs are the material which can have both properties. In the future, we expect that FGMs are used in the various engineering applications. A functionally graded interlayer can reduce the thermal stresses caused by the material constant mismatch between a ceramic and a metal. And it is well-known that the thermal stress distributions in a transient state can show large value compared with the one in a steady state. Then, the analytical studies concerned with transient thermoelasticity become important. The transient thermoelastic problems of laminated composite strip and laminated hollow cylinder with an interlayer of functionally graded material were analyzed exactly [1,2]. In this paper, we analyze the transient thermoelastic problem for a laminated composite hollow sphere with an interlayer of functionally graded material, and obtain the exact solution for the one-dimensional temperature change and thermoelastic response. 2. Analysis

A composite Latin rectangle and nonstandard strip block design

Considered is an unusual split plot design. The whole plot part is a Latin rectangle design, while the split plot part derives from a nonstandard strip block design. For the strip block part, there are two treatment factors that are randomized to strips across the whole plot experimental units, not to strips within each whole plot experimental unit. The result is five split plot error terms, not three as in a standard strip block design. The mixed model analysis and optimal exact tests for all treatment effects are developed geometrically. The analysis is illustrated by example and concluding remarks on replicated designs are offered.

Transient Thermoelastic Analysis for a Laminated Composite Strip with an Interlayer of Functionally Graded Material

This paper is concerned with the theoretical treatment of transient thermal stress problem involving a laminated composite thick strip with an interlayer of functionally graded material due to nonuniform heat supply in the width direction. The thermal and thermoelastic constants of the interlayer of functionally graded material are assumed to vary exponentially in the thickness direction. We obtain the exact solution for the two-dimensional temperature change in a transient state, and thermal stresses of a simple supported strip under the state of plane strain. Some numerical results for the temperature change, the displacement and the stress distributions are shown in figures. Furthermore, the influence of the thickness and position of the interlayer is investigated.

Fatigue behaviour of CFRP concrete joints under shear

This paper proposes a new methodology for determining stiffness and degradation of stiffness at the interface between externally bonded carbon-fibre-reinforced polymer (CFRP) and structural concrete under cyclic shear loading. In this paper an experimental programme consisting of 14 push-off specimens has been conducted. The CFRP composite strips were used to strengthen concrete externally at a known failure plane to resist shear stresses in shear friction. The test set-up and supports were designed such that there is a direct shear at the CFRP-to-concrete interface. This paper describes the experimental set-up and test parameters. Experimental results for cyclic bond stress–slip behaviour, mathematical formulations for stiffness of interface and its degradation as the number of cycles increased have been obtained and discussed.

Transient Thermoelastic and Piezothermoelastic Problems of Functionally Graded Materials

This paper is concerned with the theoretical treatment of transient thermoelastic problems involving functionally graded thick plate, laminated composite strip with an interlayer of functionally graded material, and functionally graded hollow cylinder, and transient piezothermoelastic problems involving functionally graded piezoelectric cylindrical panel. The thermal, thermoelastic and piezoelectric constants of the functionally graded materials are expressed as power functions of the radial coordinate variable or exponential functions of the thickness coordinate variable. The exact solutions for the two-dimensional temperature change in a transient state, and thermoelastic or piezothermoelastic response under the state of plane strain are presented herein. Some numerical results are shown in figures.

Tensile testing of thin films supported on compliant substrates

Elastic properties of thin films are routinely measured by straining them on a flexible carrier substrate. Stress–strain characteristics for the film/substrate composite strip are obtained and a simple mixture theory is used to extract the elastic properties of the film by assuming a uniform one-dimensional tensile stress distribution within the film thickness. In this paper, we examine the validity of using this simple theory by determining the three-dimensional elastic stress field in a composite strip. Three sample geometries and loading configurations are considered. In case A, the film is coated on one side of the carrier substrate while in case B, the carrier substrate is coated on both sides. For both case, the external load is applied only on the substrate. In case C, the geometry was the same as case A, but the external load was applied to both the film and the substrate. For film to substrate moduli ratios less than 5, the mixture theory provided adequate results with errors less than 10% for all cases considered. However, for case A, the rule of mixtures theory tends to significantly overestimate the tensile stress in the film for moduli ratio exceeding 5. An error analysis is also presented which provides guidance regarding the minimum film thickness necessary to attain results with a given accuracy. Overall the results presented in this paper provide researchers with rules to design the sample geometry and film thickness to accurately determine the elastic properties of thin films using the composite film/strip experiment. These rules are exemplified by measuring the elastic properties of a thin sputtered Al film and a hexagonal honeycomb structured Si/polymer composite film produced through an evaporation induced self-assembly process. In both cases, films are deposited on a flexible Kapton substrate and strained using a home-built film tester.

Antiplane deformation of a cracked composite strip

We obtain the analytic solution of an antiplane problem of the theory of elasticity for a cracked layer made of a composite material whose cross section is formed by a periodic array of repeated rectangular elements. Each element, in turn, contains four rectangular cells of different types. A crack is located on one of the interfaces of materials of these cells. The distributions of displacements on the outer surfaces of the layer are regarded as given. The numerical analyses are performed for the stress intensity factors depending on the mechanical properties of materials and the sizes of the cells.

Fabrication of Al/SiC P composite strips by repeated roll-bonding (RRB) process

In the present study, Al/SiC P composites were fabricated in the form of strips by repeated roll-bonding process, referred as RRB process, at room temperature, successfully. In this process, at first the SiC powders dispersed between the aluminum strips, the strips stacked over each other, and then they were fastened at both end by steel wires and roll-bonded in a few cycles, with a specific draft percentage of reduction, where the strips were annealed before every roll-bonding process. Microstructure of the fabricated composites after seven RRB cycles, showed a well-distributed SiC particles inside the layers with no significant remained porosities between them. The results also proved that the tensile strength of the composites increased with the number of RRB cycles and reached a maximum value of 123 MPa after seventh cycle which is 1.5 times higher than that of the monolithic aluminum produced by the same method.