Debonding Of Reinforcement Research Articles

Reliability Analysis of Fatigue Crack Growth in Plain Concrete

Civil engineers know that fatigue indicates themajority of structural failures. In plain and reinforced concrete structures, fatigue might account for excessivedeformation, excessive of crack widths, de-bonding ofreinforcement and rupture of the reinforcement, all of thesecan lead to structural collapse. Fatigue crack propagation can be a method to predict a remaining life of structures.Herein some works that have been done will be shown inorder to analyse the fatigue crack growth for plain concretespecimens. The goals of this study are to estimate the criticalcrack length and remaining life of a plain concrete specimen, determine the state of the specimen either havingfailed or being safe using first order reliability method(FORM) and assess which parameter has most influence onthe reliability index

Robustness assessment of precast concrete connections using component-based modelling

Employing highly optimised precast concrete product-based building solutions increases on-site productivity through elimination of formwork and reduction in propping as well as reducing waste, accidents and embodied carbon. The construction related benefits of precast concrete product-based building solutions are maximised by eliminating structural topping and designing connections between members for ease of assembly. A key challenge in the design of precast concrete buildings is the achievement of robustness under accidental loading. In this paper, sudden column removal is used to assess the robustness of a precast-concrete building system without structural topping. In this case, the development of an alternative load path under sudden column removal relies on the joint response. Joint behaviour is replicated using a component-based design procedure which captures localised failure modes. Robustness is evaluated using a ductility-centred approach and quantified in terms of the pseudo-static resistance. Two types of connection are considered for the provision of continuity at a critical half-lapped joint. The first is a plated connection which was designed initially to meet the tying requirements outlined in Eurocode 2. Under sudden column removal the plated connection’s deformational capacity is limited, which in turn reduces the pseudo-static resistance. An alternative bracketed coupler connection is proposed in which the ductility supply is controlled through debonding of reinforcement. The design concept for the bracketed connection is validated with test results from two full scale sub-assemblies. The experimental results are used to validate a component-based numerical model which is subsequently used to investigate the influence of boundary conditions, and debonding length on the pseudo-static resistance following sudden column loss. The paper shows that the pseudo-static resistance can be significantly enhanced by flexure and compressive membrane action. Consequently, the authors suggest that connection design in precast concrete structures without topping should be based on a realistic assessment of the ability of the structure to develop alternative load paths following instantaneous column removal rather than simplified tying rules.

Seismic response of precast bridge columns with composite non-proprietary UHPC filled ducts ABC connections

Accelerated bridge construction (ABC) utilizes advanced planning, new construction techniques and innovative detailing to expedite construction of new bridges or rehabilitation and replacement of old deteriorated bridges. ABC has been widely used in low seismic regions and mostly implemented in the superstructure elements but much less considered for substructure elements such as column-base connections, especially in moderate and high seismic regions. While robust seismic ABC connections have been developed using ultra-high performance concrete (UHPC), sole sourcing of robust commercial UHPC mixes is causing bidding issues and limiting the wide adoption of such seismic ABC connections. Thus, validating alternative solutions that use non-proprietary materials could help overcome such challenges. This paper presents experimental and analytical investigation of the structural and seismic behavior of precast bridge columns with non-proprietary UHPC-filled ducts column-to-footing connections. For this study, a recently developed non-proprietary UHPC mix at the University of Nevada, Reno (UNR) is used. Two large-scale column models, varied only in reinforcement debonding, were tested at UNR under combined axial and cyclic lateral loading to evaluate their seismic performance. The column models were compared with reference cast-in-place column models and another column model incorporating proprietary commercial UHPC-filled duct connection from previous studies. The test results showed that the column models were emulative of conventional connections. Analytical modeling for the two tested columns was also conducted and shown to successfully reproduce the local and global behaviors of column models with acceptable accuracy when bond-slip and bar debonding effects are properly considered.

Seismic behavior of precast concrete beam-column joints with steel strand inserts under cyclic loading

This paper experimentally investigated the seismic behavior of 9 full-scale reinforced concrete (RC) joints—8 precast RC joints and 1 cast-in-place RC joint—under cyclic loading. The precast concrete (PC) joints were divided into 3 types: cast-in-place, precast beam cast-in-place column, and fully precast with assembly. With the presence additional reinforcement at the joint core and debonding of reinforcement in some joints, the PC joints differed with other types of joints. The experimental results, such as hysteretic behavior, energy dissipation capacity and stiffness degradation, were analyzed, which showed that the PC joints with steel strands anchored into the joint core zone could meet the seismic code requirements. Additionally, a finite elementanalysis of the new type of PC joint was performed numerically, and the predicted seismic performance was in very good agreement with the experimental results. Finally, a skeleton model of the PC joint was established through parameter analysis.

A novel approach towards prediction of subsurface damage during machining metal matrix composites

Metal matrix composites (MMCs) are utilized in various industries due to their unique characteristics. Despite their spreading applications in different fields, the MMC manufacturing industry is still facing a major challenge, particularly the prediction and improvement of the quality and integrity of machined surfaces. This paper is focused on subsurface damage, which is considered to be an important aspect of surface integrity of machined parts. A novel model for prediction of the depth of damage beneath the machined surface is presented and discussed. The model is developed through investigation of plastic deformations along with the fracture and debonding of reinforcements. Comparison with data from machining experiments is performed to verify the accuracy of model predictions.

Seismic performance of RC short columns with buckling restraint reinforcement

This paper considers the application of the buckling restraining concept in reinforced-concrete (RC) columns subjected to seismic-type loading. The main objective of the experimental study is to investigate the seismic performance of RC short columns with buckling-restrained casing provided to the main reinforcement at the critical region. The debonding of reinforcement by providing a rebar restraining collar is carried out at the plastic hinge region where maximum bending moment occurs. The columns are subjected to quasi-static cyclic lateral loading combined with a constant axial loading to simulate seismic-type loading. The performance of these columns is compared – in terms of ultimate load, ductility, load displacement envelope and energy dissipation capacity – with that of counterpart short columns designed as per Indian Standard code IS:456-2000 and ductile detailing as per IS:13920-2016. The main variables selected in this investigation are the axial load ratio and the length of the buckling-restrained casing of reinforcement. The test results indicate that the columns with buckling-restrained casings have improved performance in terms of lateral load-carrying capacity, energy dissipation characteristics and reduced stiffness degradation relative to columns without casing.

Effect Hybrid Filler on the Properties of Epoxy Resin

Composites are materials which are widely used in aerospace industry for its high strength to weight ratio, where most of the alloys add weight as penalty. These composites are made up of two phases namely matrix phase and reinforcement phase. Matrix is the most important phase as it has to hold the reinforcement and to distribute the loads to the reinforcement i.e., the matrix should be adhesive and as well strong enough to resist de-bonding of reinforcement due to load acting on it. To improve certain properties of the matrix system fillers are added to it. Some filler may improve certain properties, while others reduce certain properties and improve some other properties. Combination of two or more fillers (hybrid filler system) can also be added to the matrix in certain proportion to improve its property. This work mainly concentrates on the effects addition of 1% by weight of hybrid fillers on the properties of the matrix system. Two selected filler system is mixed in the predefined proportion and added to the matrix system to prepare specimen. These specimens were tested for its flexural properties and compared with the neat matrix system.

A Comparative Study on the Dry Sliding Wear Behavior of Mild Steel and 6061Al-15wt.%SiCp Composite

Alumina-steel sliding contacts are often encountered in industrial applications. Aluminum metal matrix composite (AlMMC) is considered as a suitable replacement for ferrous materials. However, Alumina-steel/AlMMC tribological system has not been readily investigated. Accordingly, in this research work, the dry sliding wear characteristic of 6061Al-15wt.%SiCp composite and mild steel against an alumina disk is investigated and compared at three loads (10, 30, and 50 N). In mild steel, the wear mechanism envisages a mild adhesive wear at low load (10 N), while abrasive wear and oxidative wear at higher loads (30 and 50 N). The overall wear rate linearly increased with increasing load. In 6061Al-15wt.%SiCp composite, at all loads, the basic wear mechanism involves abrasive wear with de-bonding of SiC particles and oxidative wear. A non-linear relationship between wear rate and load indicates higher severity of wear loss. Particularly at higher load, the 6061Al-15wt.%SiCp composite suffers from extensive wear loss (26 times higher wear rate at 50 N load) as compared to mild steel. This indicates the unsuitability of using 6061Al-15wt.%SiCp composite as a replacement for mild steel under severe abrasive wear situation. The higher wear severity of 6061Al-15wt.%SiCp composite is attributed to the following: (i) de-bonding of reinforcement (SiC) particles reducing the material strength and subsequent removal of matrix material by micro-chipping mechanism; and (ii) an intense oxidation of 6061Al matrix under frictional heat and subsequent removal of oxide layer.

Micromechanical modeling of nanocomposites considering debonding of reinforcements

Abstract This paper deals with a constitutive model of particulate-reinforced nanocomposites which can describe the debonding damage, elasto-plastic behavior of matrix and particle size effects on deformation and damage. An incremental damage model of particulate-reinforced composites based on the Mori–Tanaka’s mean field concept, considering the particle size in nanoscale is further developed to consider the debonding of reinforcements in nanocomposites. The applicability of the proposed theory is investigated for nanocomposites consisting of Al2O3 nanoparticles with different size embedded in magnesium alloy (AZ31 and ZK60A) and pure magnesium (Mg) matrix. Based on the present model, analysis of stress–strain response for Al2O3–AZ31 nanocomposite under uniaxial tension is carried out. The effects of particle size and adhesive energy of nanoparticles at interface on stress–strain response of Al2O3–AZ31 nanocomposite is obtained. Moreover, in this paper the effect of debonding of reinforcements on effective Young’s modulus and toughness of the particulate reinforced nanocomposites is demonstrated. When the debonding damage starts to occur, the stress–strain curve for the damaged nanocomposite deviate to lower stress from those for the perfect composite. The influences of adhesive energy at interface and particle size on the stress–strain curve are considerable. Composites with lower adhesive energy at interface and larger particle size have poor toughness due to lower area under the stress–strain curve. In addition, Progressive debonding leads to a loss of stiffness in nanocomposites.

Micromechanical modeling of smart composites considering debonding of reinforcements

Using the information of the microstructure, this paper presents the development of an incremental constitutive law governing the response of an electro-magneto-thermo-mechanical smart composite. In this development, different shapes of reinforcements that have magneto-electro-thermo-elastic properties that differ from the matrix material are considered. Shapes such as ellipsoidal (spherical, prolate and oblate) particles, elliptical and circular cylindrical fibers, disk and ribbon can be treated provided that the corresponding Eshelby tensor is used. The debonding of the reinforcements from the matrix is also a part of the microscopic process considered. The developed incremental constitutive law not only predicts the macroscopic and microscopic electro-magneto-thermo-mechanical-elastic behavior of composites while considering the debonding process, but it also characterizes their different macroscopic effective properties such as permittivity, permeability, stiffness moduli, pyroelectricity, pyromagnitivity and thermal expansion coefficient in different directions. Moreover, the developed constitutive law is applicable to porous materials and composites with multiple reinforcements and porosities. In the two examples considered below, particular attention is devoted to assessing the effects of both the shape and the concentration of the inclusion and/or porosity and the damage evolution on the multiphysical microscopic and macroscopic behaviors and the effective properties. The first example sheds light on obtaining the macroscopic effective properties, taking into account the piezoelectric BaTiO 3 continuous fibers embedded in the piezomagnetic CoFe 2O 4 matrix. While in the second example, mechanical loading is considered, epoxy is taken as the matrix material and the response of the composite is presented while the evolution of damage in terms of debonding is taking place.

Abrasive wear behaviour of laser sintered iron–SiC composites

Direct metal laser sintering (DMLS) is one of the popular rapid prototyping technologies for producing metal prototypes and tooling of complex geometry in a short time. However, processing of metal matrix composites (MMCs) by laser sintering is still in infant stage. Thermal cracks and de-bonding of reinforcements are reported while processing MMCs by laser sintering process. There are reports on use of metallic-coated ceramic reinforcements to overcome these problems. The present investigation is aimed at using nickel-coated SiC in developing iron composites by DMLS technique and to characterize its abrasive wear behaviour. Microstructure, microhardness, and abrasive wear tests have been carried out on both DMLS iron and its composites sintered at a laser scan speed of 100 mm/s. Abrasion wear tests have been carried out using a pin-on-disc type machine. SiC abrasive papers of grit size 60, 80, and 150 having an average particle size of 268, 192, and 93 μm, respectively, have been used. Load was varied between 5 and 25 N in steps of 5, while the sliding distance and sliding velocity of 540 m and 2.5 m/s, respectively was adopted for all the tests. Optical, scanning electron micrograph and surface roughness observation of worn surfaces have been undertaken. An increase in microhardness and a decrease in density of the laser sintered iron–SiC composites was observed with increase in SiC content. The abrasive wear resistance of composites increases with increased content of SiC in iron matrix. For a given grit size of SiC abrasive paper, at all the loads studied, iron–SiC composites exhibit excellent abrasive wear resistance. Increase in abrasive wear was observed with the increase in abrasive particle size.

Damage of 6061/SiCw composite by thermal cycling

The unreinforced 6061 alloy and a 6061/SiC composite, at the beginning of the T6 temper, were submitted to thermal cycling (up to 2000 cycles) in the temperature ranges 25–180 °C and 25–220°C. The microstructure of these materials was studied by scanning electron microscopy and mercury intrusion porosimetry. Mechanical and thermomechanical properties were also investigated. Tensile strength, hardness, Charpy impact resistance, fracture toughness, density, specimen dimensions and thermal expansion were compared before and after thermal cycling. The unreinforced alloy showed an increase of ductility with cycling. This behaviour was chiefly due to overageing and partial annealing. The composite material, following the thermal treatment, did not only undergo overageing and annealing of its metal matrix; void coalescence, crack formation and reinforcement debonding were also observed. The development of these defects basically resulted in a marked decrease of tensile strength, yield strength, Charpy impact energy and fracture toughness.

Toughening of Intermetallics by Coated Ductile Reinforcements

AbstractThe effects of reinforcement debonding and work hardening on ductile reinforcement toughening of γ-TiAl have been examined. Debonding has been varied by either the development of a brittle reaction product layer or by depositing a thin oxide coating between the reinforcement and matrix. The role of work hardening has been explored by comparing Nb reinforcements that exhibits high work hardening with solution hardened Ti-Nb alloy that exhibits negligible work hardening. It is demonstrated that a high work of rupture is encouraged by extensive debonding when the reinforcement exhibits high work hardening. Conversely, debonding is not beneficial when the reinforcement exhibits low work hardening.