Tensile Strain Capacity Prediction of Engineered Cementitious Composites (ECC) Using Soft Computing Techniques

Plain concrete is strong in compression but brittle in tension,having a low tensile strain capacity that can significantly degrade the long-term performance of concrete structures,even when steel reinforcing is present.In order to address these challenges,short polymer fibers are randomly dispersed in a cement-based matrix to forma highly ductile engineered cementitious composite(ECC).Thismaterial exhibits high ductility under tensile forces,with its tensile strain being several hundred times greater than conventional concrete.Since concrete is inherently weak in tension,the tensile strain capacity(TSC)has become one of the most extensively researched properties.As a result,developing a model to predict the TSC of the ECC and to optimize the mixture proportions becomes challenging.Meanwhile,the effort required for laboratory trial batches to determine the TSC is reduced.To achieve the research objectives,five distinct models,artificial neural network(ANN),nonlinear model(NLR),linear relationship model(LR),multi-logistic model(MLR),and M5P-tree model(M5P),are investigated and employed to predict the TSCof ECCmixtures containing fly ash.Data from115 mixtures are gathered and analyzed to develop a new model.The input variables include mixture proportions,fiber length and diameter,and the time required for curing the various mixtures.The model’s effectiveness is evaluated and verified based on statistical parameters such as R2,mean absolute error(MAE),scatter index(SI),root mean squared error(RMSE),and objective function(OBJ)value.Consequently,the ANN model outperforms the others in predicting the TSC of the ECC,with RMSE,MAE,OBJ,SI,and R2 values of 0.42%,0.3%,0.33%,0.135%,and 0.98,respectively.

Effect of Curing Age on Tensile Properties of Fly Ash Based Engineered Geopolymer Composites(FA-EGC)by Uniaxial Tensile Test and Ultrasonic Pulse Velocity Method

Tensile properties of fly ash based engineered geopolymer composites(FA-EGC)at different curing ages were studied by uniaxial tensile test and ultrasonic pulse velocity(UPV)methods,which included uniaxial tensile properties,the correlation between ultrasonic pulse velocity and tensile properties,and characteristic parameters of microcracks.The experimental results show that obvious strain hardening behavior can be found in FA-EGC at different curing ages.With the increase of curing age,the tensile strength increases,the tensile strain decreases and the toughness becomes worse.The UPV of FA-EGC increases with curing age,and a strong correlation can be found between tensile strength and UPV.With the increase of curing age,the average crack width of FA-EGC decreases and the total number of cracks increases.This is because the strength of geopolymer increases fast at early age,thus the later strength development of FA-EGC tend to be stable.At the same time,the bond strength between fiber and matrix,and the friction of fiber/matrix interface continue to increase with curing age,thus the bridging effect of fiber is gradually strengthened.In conclusion,the increase of curing age is beneficial to the development of tensile properties of FA-EGC.

Microstructural characterization and mechanical properties of(TiC+TiB)/TA15 composites prepared by an in-situ synthesis method

Titanium matrix composites reinforced with ceramic particles are considered a promising engineering material due to their combination of high specific strength,low density,and high modulus.In this study,the TA15-based composites reinforced with a volume fraction of 10% to 25%(TiB+TiC)were prepared using powder metallurgy and casting technique.Microstructural characterization and phase constitution were examined using optical microscopy(OM),scanning electron microscopy(SEM),and X-ray diffraction(XRD).In addition,the microhardness,room temperature(RT)and high temperature(HT)tensile properties of the composites were evaluated.Results revealed that the reinforcements are distributed uniformly even in the composites with a high volume of TiB and TiC.However,as the volume fraction exceeds 15%,TiB and TiC particles become coarsening and exhibit rod-like and dendritic-like morphology.Microhardness increases gradually from 321.2 HV for the base alloy to a maximum of 473.3 HV as the reinforcement increases to 25vol.%.Tensile test results indicate that a reinforcement volume fraction above 20% is beneficial for enhancing tensile strength and yield strength at high temperatures,but it has an adverse effect on room temperature elongation.Conversely,if the reinforcement volume fraction is below 20%,it can improve high-temperature elongation when the temperature exceeds 600℃.

Influence of B4C and ZrB2 reinforcements on microstructural,mechanical and wear behaviour of AA 2014 aluminium matrix hybrid composites

Considering their affordability and high strength-to-weight ratio,lightweight aluminium alloys are the subject of intensive research aimed at improving their properties for use in the aerospace industry.This research effort aims to develop novel hybrid composites based on AA 2014 alloy through the use of liquid metallurgy stir casting to reinforce dual ceramic particles of Zirconium Diboride(ZrB_(2))and Boron Carbide(B4C).The weight percentage(wt%)of ZrB_(2) was varied(0,5,10,and 15),while a constant 5 wt%of B4C was maintained during this fabrication.The as-cast samples have been assessed using an Optical Microscope(OM)and a Scanning Electron Microscope(SEM)with Energy Dispersive Spectroscopy(EDS).The properties such as hardness,tensile strength,and wear characteristics of stir cast specimens were assessed to examine the impact of varying weight percentages of reinforcements in AA 2014 alloy.In particular,dry sliding wear behaviour was evaluated considering varied loads using a pin-on-disc tribotester.As the weight%of ZrB_(2) grew and B4C was incorporated,hybrid composites showed higher hardness,tensile strength,and wear resistance.Notably,the incorporation of a cumulative reinforcement consisting of 15 wt%ZrB_(2) and 5 wt%B4C resulted in a significant 31.86%increase in hardness and a 44.1%increase in tensile strength compared to AA 2014 alloy.In addition,it has been detected that wear resistance of hybrid composite pin(containing 20 wt%cumulative reinforcement)is higher than that of other stir cast wear test pins during the whole range of applied loads.Fractured surfaces of tensile specimens showed ductile fracture in the AA 2014 matrix and mixed mode for hybrid composites.Worn surfaces obtained employing higher applied load indicated abrasive wear with little plastic deformation for hybrid composites and dominant adhesive wear for matrix alloy.Hence,the superior mechanical and tribological performance of hybrid composites can be attributed to dual reinforcement particles being dispersed well and the effective transmission of load at this specific composition.

Microstructure,interfacial reaction behavior,and mechanical properties of Ti_3AlC_(2)reinforced Al6061 composites

The interfacial reaction behavior of Al and Ti_3AlC_(2)at different pouring temperatures and its effect on the microstructure and mechanical properties of the composites were investigated.The results show that the addition of3.0 wt.%Ti_3AlC_(2)refines the average grain size ofα(Al)in the composite by 50.1%compared to Al6061 alloy.Morphological analyses indicate that an in-situ Al_(3Ti)transition layer of-180 nm in thickness is generated around the edge of Ti_3AlC_(2)at 720℃,forming a well-bonded Al-Al_(3Ti)interface.At this processing temperature,the ultimate tensile strength of A16061-3.0 wt.%Ti_3AlC_(2)composite is 199.2 MPa,an improvement of 41.5%over the Al6061 matrix.Mechanism analyses further elucidate that 720℃is favourable for forming the nano-sized transition layer at the Ti_3AlC_(2)edges.And,the thermal mismatch strengthening plays a dominant role in this state,with a strengthening contribution of about 74.8%.

TENSILE STRENGTH OF RANDOM ORIENTED SHORT FIBER COMPOSITE

This paper shows a calculation model and a method for predicting the tensile strength of the random distributed short fiber composite.On the basis of Renjie Mao's model,the longitudinal tensile strength of the aligned short fiber composite is formulated.Considering the transverse tensile strength and in plane shear strength of the unidirectional fiber composite,and the stress transformation relations of two couples of axes,the stress of the unidirectional fiber composite when it is loaded at an arbitrary angle is obtained.With the aid of an equivalence relation,the calculation formulation of the tensile strength of the random short fiber reinforced composite is deduced.

Carbon Fiber Breakage Mechanism in Aluminum(Al)/Carbon Fibers(CFs) Composite Sheet during Accumulative Roll Bonding(ARB) Process

We put forward a method of fabricating Aluminum(Al)/carbon fibers(CFs) composite sheets by the accumulative roll bonding(ARB) method. The finished Al/CFs composite sheet has CFs and pure Al sheets as sandwich and surface layers. After cross-section observation of the Al/CFs composite sheet, we found that the CFs discretely distributed within the sandwich layer. Besides, the tensile test showed that the contribution of the sandwich CFs layer to tensile strength was less than 11% compared with annealed pure Al sheet. With ex-situ observation of the CFs breakage evolution with-16%,-32%, and-45% rolling reduction during the ARB process, the plastic instability of the Al layer was found to bring shear damages to the CFs. At last, the bridging strengthening mechanism introduced by CFs was sacrificed. We provide new insight into and instruction on Al/CFs composite sheet preparation method and processing parameters.

Effect of glass fibre(GF) addition on microstructure and tensile property of GF/Pb composites fabricated by powder metallurgy

GF/Pb compositeswerefabricated by the method of powder metallurgy, and the density, microstructure and tensile propertywerecharacterized considering the size and content ofglass fibre （GF）. The results show that relative densities decrease with increasing GF fraction, and the 50μm-GF reinforced specimens exhibit a better densification than the 300μm-GF reinforced ones. The GF particles distribute quite uniformly inPb matrix, and the composites fabricated at low sintering temperature （〈200℃） possess fine-grain microstructure. The addition of GF significantly improves the strength of the Pb composites, and the ultimate tensile strength of the Pb composite reinforcedwith the addition of 50μm-0.5% GF（mass fraction）is about 30MPa higher than that of GF-free sample. For all composites groups, increasing the reinforcement content from 0.5%to 2%（mass fraction）results in a decrease in both tensile strength and ductility.

Tensile Properties of Weft Knitted Fabric Reinforced Composites

Seven kinds of weft knitted fabrics from glass fiber yarns were used as reinforcement to make fabric/epoxy composite laminates. Tensile tests were carried out to examine and compare the mechanical properties in course and wale direction of these composites. On the basis of experimental results, attempts have been made to analyze some main factors influencing stress-strain curve, ultimate tensile strength and initial elastic modulus of specimens.

Tensile Properties of Surface-Treated Glass Fiber Reinforced PTFE Composite with Rare Earth Elements

The optimum amount of rare earth elements (RE) for treating glass fiber surface and its effect on the tensile properties of glass fiber reinforced polytetrafluoroethylene (GF/PTFE) composites were investigated. The tensile properties of GF/PTFE composites with different surface treatment conditions were measured. The fracture surface morphologies were observed and analyzed by SEM. The results indicate that rare earth elements can effectively promote the interfacial adhesion between the glass fiber and PTFE, owing to the effects of rare earth elements on the compatibility. The tensile properties of GF/PTFE composites can be improved considerably when the content of RE in surface modifier is 0.2%～0 4%, and the optimum performance of GF/PTFE composites is obtained at 0.3%RE content.

Effect of Bi modification treatment on microstructure,tensile properties,and fracture behavior of cast Al-Mg_2Si metal matrix composite

Bi has a good modification effect on the hypoeutectic Al-Si alloy, and the morphology of eutectic Si changes from coarse acicular to fine fibrous. Based on the similarity between Mg2Si and Si phases in crystalline structure and crystallization process, the present study investigated the effects of different concentrations of Bi on the microstructure, tensile properties, and fracture behavior of cast Al-15wt.%Mg2Si in-situ metal matrix composite. The results show that the addition of the proper amount of Bi has a significant modification effect on both primary and eutectic Mg2Si in the Al-15wt.%Mg2Si composite. With an increase in Bi content from 0 to lwt.%, the morphology of the primary Mg2Si is changed from irregular or dendritic to polyhedral shape; and its average particle size is significantly decreased from 70 to 6 μm. Moreover, the morphology of the eutectic Mg2Si phase is altered from flake-like to very short fibrous or dot-like. When the Bi addition exceeds 4.0wt.%, the primary Mg2Si becomes coarse again. However, the eutectic Mg2Si still exhibits the modified morphology. Tensile tests reveal that the Bi addition can improve the tensile strength and ductility of the material. Compared with those of the unmodified composite, the ultimate tensile strength and percentage elongation after fracture with 1.0wt.% Bi increase 51.2% and 100%, respectively. At the same time, the Bi addition changes the fracture behavior from brittle to ductile.

Effects of compocasting process parameters on microstructural characteristics and tensile properties of A356-SiC_p composites

The effects of compocasting process parameters on some structural and tensile characteristics of the A356-10% SiCp (volume fraction) composites were studied. Semisolid stirring was carried out at temperatures of 590, 600 and 610 °C with stirring speeds of 200, 400 and 600 r/min for 10, 20 and 30 min. The distribution of the SiC particles within the matrix, porosity content and tensile properties of the obtained samples were examined. The structural evaluations show that by increasing the stirring time and decreasing the stirring temperature, the uniformity in the particle distribution is improved;however, by increasing the stirring speed the homogeneity firstly increases and then declines. It is also found that by increasing all of the processing parameters, the porosity content is enhanced. From the tensile characteristics viewpoint, the optimum values of the speed, temperature and time are found to be 400 r/min, 590 °C and 30 min, respectively. The contribution of the reinforcement distribution uniformity prevails over that of the porosity level to the tensile properties.

Effect of Ultraviolet Aging on the Bonding and Tensile Properties of Polymer-Cement Composite

In this paper,the specimens of polymer-cement composites after 1 d,7 d,15 d,and 30 d aging without aging and UV aging are subjected to fixed extension test and tensile test.By observing the mode of the composite in the fixed-elongation test,and measuring the elastic recovery rate,tensile strength,elongation at break,peak tensile strain,tensile toughness and pre-peak tensile toughness of the composite,the effects of UV aging on the bonding and the tensile properties of the composite were studied.And combining with scanning electron microscopy experiments,the micro-mechanism of the effect of ultraviolet aging on the properties of composite was analyzed.The results showed that the composite had a good bonding property,and no damage was observed after UV aging for 30 days.The UV aging increased the elastic recovery rate and peak tensile within a certain range.The elastic recovery rate and peak tensile strain of the composite increased by 6.60%and 23.55%respectively after UV aging for 15 days.Therefore,the UV aging could enhance the tensile property and the tensile energy consumption performance of the composite.The tensile strength of the composite increased by 65.36%after UV aging for 30 days.The tensile toughness and pre-peak tensile toughness of the composite were increased by 43.29%and 101.83%respectively after UV aging for 15 days.The elongation at break of composite decreased continuously after UV aging due to the photo-oxygen reaction,as well as secondary hydration reaction and cross-linking curing reaction of cement.

Preliminary Study on Tensile and Impact Properties of Kenaf/Bamboo Fiber Reinforced Epoxy Composites

The application of natural fibers as reinforcement in composite material has increased due to environmental concerns,low cost,degradability and health concerns.The purpose of this study is to identify the best type of bamboo fibers to be used as reinforcement for kenaf(K)/bamboo hybrid composite.There were three types of bamboo fibers evaluated in this study which include bamboo mat(B),bamboo fabric(BF)and bamboo powder(BP).Chemical composition of B,BF,BP and K fibers were analyzed in this study.The effect of different types of bamboo fibers on tensile,impact,and morphological properties were investigated.The B/epoxy composites displayed the highest tensile strength(53.03 MPa)while K/epoxy composite had the highest tensile modulus(4.71 GPa).Scanning electron micrographs of B/epoxy composites displayed better fiber/matrix interfacial bonding in comparison to other studied composites.Results showed that impact strength of BF-based composite was highest(45.70 J/m).In conclusion,the tensile strength of B/epoxy composite is superior to the other bamboo reinforced composites and will be further evaluated in the next study.

Prediction of influence of process parameters on tensile strength of AA6061/TiC aluminum matrix composites produced using stir casting

Stir casting was used to produce AA6061/15%TiC （mass fraction） aluminum matrix composites （AMCs）. An empirical relationship was developed to predict the effect of stir casting parameters on the ultimate tensile strength （UTS） of AA6061/TiC AMCs. A central composite rotatable design consisting of four factors and five levels was used to minimize the number of experiments, i.e., castings. The factors considered were stirring speed, stirring time, blade angle and casting temperature. The effect of those factors on the UTS of AA6061/TiC AMCs was derived using the developed empirical relationship and elucidated using microstructural characterization. Each factor significantly influenced the UTS. The variation in the UTS was attributed to porosity content, cluster formation, segregation of TiC particles at the grain boundaries and homogenous distribution in the aluminum matrix.

Effect of cold-rolling on tensile strength of SiCw/Al composite

SiC_w/Al composite was fabricated through a squeeze cast route and coldrolled to about 30 percent, 50 percent and 70 percent reduction In thickness, respectively. Thelength of whiskers in the composite before and after rolling was examined using SEM. Some of therolled composites were recrystallization annealed to remove the work hardening of matrix alloy. Thetensile strength of the rolled and annealed SiC_w/Al composites was examined and then associatedwith the change of the whisker length and the work hardening of matrix alloy. It was found that thetensile strength is a function of the degree of cold rolling. For the cold rolled composites, withthe increase in the degree of cold rolling, the tensile strength increases at first, and decreaseswhen the degree of cold rolling exceeds 50 percent. For the annealed ones, however; the tensilestrength decreases monotonously with the increase in rolling degree. The different changes intensile strength between the rolled and annealed composites could be attributed to the result of thecompetition between the work hardening of matrix resulting from the cold rolling and the worksoftening arising from the change of whisker length.

Effects of Matrix on Tensile Strength of SiCw/Al Composites

Fine grains and high density of dislocations in the matrix increase the tensile strength of SiCw/Al composites.Increased matrix strength leads to the decrease of the critical length of whisker,which makes more whiskers effectively reinforce the matrix,so the tensile strength of the SiCw/Al composite is further increased.

Fabrication characteristics and tensile strength of novel Al2024/SiC/red mud composites processed via stir casting route

The stir casting technique was used to fabricate aluminum2024matrix hybrid composites reinforced with SiC(5%,mass fraction)and red mud(5%-20%,mass fraction)particles.The developed composites were characterized by using scanning electron microscopy(SEM)and electron dispersive spectrum(EDS)techniques.Further,Taguchi’s approach of experimental design was used to examine the tensile strength of the hybrid composites(with minimum number of experiments).It was found that the reinforcing particles were well dispersed and adequately bonded in the hybrid composites.The density and porosity of the hybrid composites were reduced with the increase in reinforcement content.The tensile strength of the composites increased with the increase in the red mud content and the ageing time.The developed model indicated that the red mud content had the highest influence on the tensile strength response followed by the ageing time.Overall,it was found that Al2024/SiC/red mud composites exhibited superior tensile strength(about34%higher)in comparison to the Al2024alloy under optimized conditions.

Monotonic tensile behavior analysis of three-dimensional needle-punched woven C/SiC composites by acoustic emission

High toughness and reliable three-dimensional needled C/SiC composites were fabricated by chemical vapor infiltration （CVI）. An approach to analyze the tensile behaviors at room temperature and the damage accumulation of the composites by means of acoustic emission was researched. Also the fracture morphology was examined by S-4700 SEM after tensile tests to prove the damage mechanism. The results indicate that the cumulative energy of acoustic emission （AE） signals can be used to monitor and evaluate the damage evolution in ceramic-matrix composites. The initiation of room-temperature tensile damage in C/SiC composites occurred with the growth of micro-cracks in the matrix at the stress level about 40% of the ultimate fracture stress. The level 70% of the fracture stress could be defined as the critical damage strength.

In-plane Tensile Behaviors of Bi-axial Warp-Knitted Composites under Quasi-static and High Strain Rate Loading

The in-plane tensile behaviors of bi-axial warp-knitted(BWK) composites under quasi-static and high strain rates loading were experimentally analyzed in this article. The tensile tests were conducted along warp direction( 0°) and weft direction( 90°) at quasi-static rate of 0. 001 s^(-1) and high strain rates ranging from 1 450 to 2 540 s^(-1),respectively. It is found that the significant strain rate sensitivity can be observed in the stress-strain curves of BWK composites. The fracture morphologies of BWK composites demonstrate that the tensile failure modes are shear failure and fiber breakage under the quasi-static testing condition while interface failure and fibers pullout are at high strain rates.