Experimental study on the compressive behaviors of CFRP tube-encased concrete columns

Nine square concrete columns including 6 CFRP/ECCs and 3 concrete columns are prepared,which have cross-section of 200 mm×200 mm and height of 600 mm.The CFRP tubes with fibers oriented at hoop direction were manufactured to have 3 or 5 layers of CFRP with 10 mm, 20 mm,or 40 mm rounding corner radii at vertical edges.A 100 mm overlap in the direction of fibers was provided to ensure proper bond.Uniaxial compression tests were conducted to investigate the compressive behavior.It is evident that the CFRP tube confinement can improve the behavior of concrete core,in terms of axial compressive strength or axial deformability.Test results show that the stress-strain behavior of CFRP/ECCs vary with different confinement parameters,such as the number of confinement layers and the rounding corner radius.

Moisture effect on compressive behavior of concrete under dynamic loading

The effect of moisture content upon compressive mechanical behavior of concrete under impact loading was studied. The axial rapid compressive loading tests of over 50 specimens with five different saturations were executed. The technique "split Hopkinson pressure bar"(SHPB) was used. The impact velocity was 10 m/s with corresponding strain rate of 50 s-1. The compressive behavior of materials was measured in terms of stress-strain curves, dynamic compressive strength, dynamic increase factor(DIF) and critical strain at a maximum stress. The data obtained from test indicate that both ascending and descending portions of stress-stain curves are affected by moisture content. However, the effect is noted to be more significant in ascending portion of the stress-strain curves. Dynamic compressive strength is higher at lower moisture content and weaker at higher moisture content.Furthermore, under nearly saturated condition, an increase in compressive strength can be found. The effect of moisture content on the average DIF of concrete is not significant. The critical compressive strain of concrete does not change with moisture content.

Influence of free-end torsion on compressive behavior of extruded AZ31 rod at various temperatures

The influence of free-end torsion on compressive behavior of an extruded AZ31 rod at various temperatures was studied.Pre-torsion generates a high density of dislocations and a large number of{1012}twins in the matrix,which can largely enhance the compressive yield strength at RT and 100℃.However,with increasing temperature,hardening effect via pre-torsion gradually decreases.When the compressive temperature reaches 300℃,pre-torsion reduces the compressive yield strength.Moreover,initial dislocations and twins via torsion help to refine the sub-structure and accelerate the continuous dynamic recrystallization during compression at 200℃.Thus,twisted sample exhibits more rapid flow softening behavior than the as-extruded sample at 200℃.When compressed at 300℃,the twins and dislocations via torsion were largely eliminated during the holding time,and the discontinuous dynamic recrystallization was enhanced.It is found that the compression curves of twisted sample and as-extruded sample tended to be coincident at 300℃.Related mechanisms were discussed in detail.

Effect of deformation temperature on the hot compressive behavior of metal matrix composites with misaligned whiskers

A multi-inclusion cell model is used to investigate the effect of deformation temperature and whisker rotation on the hot compressive behavior of metal matrix composites with misaligned whiskers. Numerical results show that deformation temperature influences the work-hardening behavior of the matrix and the rotation behavior of the whiskers. With increasing temperature, the work hardening rate of the matrix decreases, but the whisker rotation angle increases. Both whisker rotation and the increase of deformation temperature can induce reductions in the load supported by whisker and the load transferred from matrix to whisker. Additionally, it is found that during large strain deformation at higher temperatures, the enhancing of deformation temperature can reduce the effect of whisker rotation. Meanwhile, the stress-strain behavior of the composite is rather sensitive to deformation temperature. At a relatively lower temperature （150℃）, the composite exhibits work hardening due to the matrix work hardening, but at relatively higher temperatures （300℃ and above）, the composite shows strain softening due to whisker rotation. It is also found that during hot compression at higher temperatures, the softening rate of the composite decreases with increasing temperature. The predicted stress-strain behavior of the composite is approximately in agreement with the experimental results.

Experimental study on axial compressive behaviors of prefabricated composite thermal insulation walls after single-side fire exposure

The axial bearing capacity of prefabricated composite walls composed of inner and outer concrete wythes,expandable polystyrene(EPS)boards and steel sleeve connectors is investigated.An experimental study on the axial bearing capacity of four prefabricated composite walls after fire treatment is carried out.Two of the prefabricated composite walls are normal-temperature specimens,and the others are treated with fire.The damage modes and crack development are observed,and the axial bearing capacity,lateral deformation of the specimens,and the concrete and reinforcing bar strain are tested.The results show that the ultimate bearing capacity of specimens after a fire is less than that of normal-temperature specimens;when the insulation board thicknesses are 40 mm and 60 mm,the decrease amplitudes are 20.8%and 16.8%,respectively.The maximum lateral deformation of specimens after a fire is greater than that of normal-temperature specimens,and under the same level of load,the lateral deformation increases as the insulation board thickness increases.Moreover,the strain values of the concrete and reinforcing bars of specimens after a fire are greater than those of normal-temperature specimens,and the strain values increase as the thickness of insulation board increases.

Experimental Study on the Compressive Behavior of CFRP/ECCs

In this study,nine square concrete columns,including six CFRP/ECCs and three plain concrete control specimen columns,were prepared. The CFRP tubes with fibers oriented in the hoop direction were manufactured with 10,20,or 40 mm rounded corner radii at vertical edges. A 100 mm overlap in the direction of fibers was provided to ensure a proper bond. Uniaxial compression tests were conducted to investigate the compressive behaviors including the axial strength,stress-strain response,and ductility. It is evident that the CFRP tube confinement can improve the compressive behavior of concrete core,in terms of axial compressive strength or axial deformability. Based on the experimental results and some existing test database attained by other researchers,a design-oriented model is developed. The predictions of the model for CFRP/ECCs show good agreement with test results.

Compressive behavior of Zn-22Al closed-cell foams under uniaxial quasi-static loading

Zn-22 Al alloy closed-cell foams were fabricated by melt foaming process using hydride foaming agent. The compressive properties were investigated under quasi-static condition. The structure of the foamed material was analyzed during compression test to reveal the relationship between morphology and compressive behavior. The results show that the stress-strain behavior is typical of closed-cell metal foams and mostly of brittle type. Governing deformation mechanism at plateau stage is identified to be brittle crushing. A substantial increase in compressive strength of Zn-22 Al foams was obtained. The agreement between compressive properties and Gibson-Ashby model was also detected.

In-situ Micro-CT analysis of deformation behavior in sandwich-structured meta-stable beta Ti−35Nb alloy

Beta Ti−35Nb sandwich-structured composites with various reinforcing layers were designed and produced using additive manufacturing(AM)to achieve a balance between light weight and high strength.The impact of reinforcing layers on the compressive deformation behavior of porous composites was investigated through micro-computed tomography(Micro-CT)and finite element method(FEM)analyses.The results indicate that the addition of reinforcement layers to sandwich structures can significantly enhance the compressive yield strength and energy absorption capacity of porous metal structures;Micro-CT in-situ observation shows that the strain of the porous structure without the reinforcing layer is concentrated in the middle region,while the strain of the porous structure with the reinforcing layer is uniformly distributed;FEM analysis reveals that the reinforcing layers can alter stress distribution and reduce stress concentration,thereby promoting uniform deformation of the porous structure.The addition of reinforcing layer increases the compressive yield strength of sandwich-structured composite materials by 124%under the condition of limited reduction of porosity,and the yield strength increases from 4.6 to 10.3 MPa.

Compressive property and energy absorption characteristic of interconnected porous Mg-Zn-Y alloys with adjusting Y addition

In this study,interconnected porous Mg-2Zn-xY alloys with different phase compositions were prepared by various Y additions(x=0.4,3,and 6 wt.%)to adjust the compressive properties and energy absorption characteristics.Several characterization methods were then applied to identify the microstructure of the porous Mg-Zn-Y and describe the details of the second phase.Compressive tests were performed at room temperature(RT),200℃,and 300℃to study the impact of the Y addition and testing temperature on the compressive properties of the porous Mg-Zn-Y.The experimental results showed that a high Y content promotes a microstructure refinement and increases the volume fraction of the second phase.When the Y content increases,different Mg-Zn-Y ternary phases appear:I-phase(Mg_(3)Zn_(6)Y),W-phase(Mg_(3)Zn_(3)Y_(2)),and LPSO phase(Mg_(12)ZnY).When the Y content ranges between 0.4%and 6%,the compressive strength increases from 6.30MPa to 9.23 MPa,and the energy absorption capacity increases from 7.33 MJ/m^(3)to 10.97 MJ/m^(3)at RT,which is mainly attributed to the phase composition and volume fraction of the second phase.However,the average energy absorption efficiency is independent of the Y content.In addition,the compressive deformation behaviors of the porous Mg-Zn-Y are altered by the testing temperature.The compressive strength and energy absorption capacity of the porous Mg-Zn-Y decrease due to the softening effect of the high temperature on the struts.The deformation behaviors at different temperatures are finally observed to reflect the failure mechanisms of the struts.

Compressive behavior and energy absorption of polymeric lattice structures made by additive manufacturing

Lattice structures have numerous outstanding characteristics,such as light weight,high strength,excellent shock resistance,and highly efficient heat dissipation.In this work,by combining experimental and numerical methods,we investigate the compressive behavior and energy absorption of lattices made through the stereolithography apparatus process.Four types of lattice structures are considered:(i)Uniform bodycentered-cubic(U-BCC);(ii)graded body-centered-cubic(G-BCC);(iii)uniform body-centered-cubic with z-axis reinforcement(U-BCCz);and(iv)graded body-centeredcubic with z-axis reinforcement(G-BCCz).We conduct compressive tests on these four lattices and numerically simulate the compression process through the finite element method.Analysis results show that BCCz has higher modulus and strength than BCC.In addition,uniform lattices show better energy absorption capabilities at small compression distances,while graded lattices absorb more energy at large compression distances.The good correlation between the simulation results and the experimental phenomena demonstrates the validity and accuracy of the present investigation method.

Compressive Behavior of Porous Titanium Fiber Materials

Porous titanium fiber materials with the fiber sizes of 70--120 μm in diameter were prepared by vacuum sintering technology. The morphology and compressive properties of porous titanium fiber materials were investigated by using a scanning electron microscope （SEM） and an MST 858 compression testing machine in quasi-static condition. The results show that porous titanium fibers form complex micro-networks. The stress-strain curves of por- ous titanium fiber materials exhibit elastic region, platform region and densification region and no collapse during platform region. The yield strength of porous titanium fiber materials decreases with increasing the porosity and increasing the fiber diameter.

Anisotropic Porous Ti6Al4V Alloys Fabricated by Diffusion Bonding:Adaption of Compressive Behavior to Cortical Bone Implant Applications

In this work, porous Ti6Al4V alloys with 30%-70% porosity for biomedical applications were fabricated by diffusion bonding of alloy meshes. Pore structure was characterized by Micro-CT and SEM. Compressive behavior in the out-of-plane direction and biocompatibility with cortical bone were studied. The results reveal that the fabricated porous Ti6Al4V alloys possess anisotropic structure with square pores in the in-plane direction and elongated pores in the out-of-plane direction. The average pore size of porous Ti6Al4V alloys with 30%-70% porosity is in the range of 240-360 Bin. By tailoring diffusion bonding temperature, aspect ratio of alloy meshes and porosity, porous Ti6Al4V alloys with different compressive properties can be obtained, for instance, Young＇s modulus and yield stress in the ranges of 4-40 GPa and 70-500 MPa, respectively. Yield stress of porous Ti6Al4V alloys fabricated by diffusion bonding is close to that of alloys fabricated by rapid prototyping, hut higher than that of fabricated by powder sintering and space-holder method. Diffusion bonding temperature has some effects on the yield stress of porous Ti6Al4V alloys, but has a minor effect on the Young＇s modulus. The relationship between compressive properties and relative density conforms well to the Gibson-Ashby model. The Young＇s modulus is linear with the aspect ratio, while the yield stress is linear with the square of aspect ratio of alloy meshes. Porous Ti6Al4V alloys with 60%-70% porosity have potential for cortical bone implant applications.

Compressive behavior of hybrid steel-polyvinyl alcohol fiber-reinforced concrete containing fly ash and slag powder:experiments and an artificial neural network model

Understanding the mechanical behavior of hybrid fiber-reinforced concrete(HFRC),a composite material,is crucial for the design of HFRC and HFRC structures.In this study,a series of compression experiments were performed on hybrid steelpolyvinyl alcohol(PVA)fiber-reinforced concrete containing fly ash and slag powder,with a focus on the fiber content/ratio effect on its compressive behavior;a new approach was built to model the compression behavior of HFRC by using an artificial neural network(ANN)method.The proposed ANN model incorporated two new developments:the prediction of the compressive stress-strain curve and consideration of 23 features of components of HFRC.To build a database for the ANN model,relevant published data were also collected.Three indices were used to train and evaluate the ANN model.To highlight the performance of the ANN model,it was compared with a traditional equation-based model.The results revealed that the relative errors of the predicted compressive strength and strain corresponding to compressive strength of the ANN model were close to 0,while the corresponding values from the equation-based model were higher.Therefore,the ANN model is better able to consider the effect of different components on the compressive behavior of HFRC in terms of compressive strength,the strain corresponding to compressive strength,and the compressive stress-strain curve.Such an ANN model could also be a good tool to predict the mechanical behavior of other composite materials.

Compressive Behavior of Wood-based 2-D Lattice Structure under Multivariable Analysis

In order to optimize the out-of-plane compression performance of the wood structure,wood-based 2-D lattice structures were designed and manufactured with oriented strand board as the panel and birch round stick as the core by using a simple insert-glue method.In this experiment,the different thicknesses of the upper and lower panels,the different shavings arrangement directions of the upper and lower panels and the different configurations of the specimens were used to analyze the compression performance of the specimens under multivariable conditions.Through the combination of experimental test and theoretical analysis,we analyzed and compared different failure types of the structure and multiple compression parameters.The results showed that the shavings arrangement direction of the panel has a more important influence on the whole specimen than the thickness of the panel,especially the transverse shavings of the panel can withstand greater shear stress than the longitudinal shavings for a specimen.

High strain rate compressive strength behavior of cemented paste backfill using split Hopkinson pressure bar

The stability of cemented paste backfill(CPB)is threatened by dynamic disturbance,but the conventional low strain rate laboratory pressure test has difficulty achieving this research purpose.Therefore,a split Hopkinson pressure bar(SHPB)was utilized to investigate the high strain rate compressive behavior of CPB with dynamic loads of 0.4,0.8,and 1.2 MPa.And the failure modes were determined by macro and micro analysis.CPB with different cement-to-tailings ratios,solid mass concentrations,and curing ages was prepared to conduct the SHPB test.The results showed that increasing the cement content,tailings content,and curing age can improve the dynamic compressive strength and elastic modulus.Under an impact load,a higher strain rate can lead to larger increasing times of the dynamic compressive strength when compared with static loading.And the dynamic compressive strength of CPB has an exponential correlation with the strain rate.The macroscopic failure modes indicated that CPB is more seriously damaged under dynamic loading.The local damage was enhanced,and fine cracks were formed in the interior of the CPB.This is because the CPB cannot dissipate the energy of the high strain rate stress wave in a short loading period.

Effects of curing age on compressive and tensile stress-strain behaviors of ecological high ductility cementitious composites

To obtain the design parameters of the structure made by ecological high ductility cementitious composites(Eco-HDCC),the effects of curing age on the compressive and tensile stress-strain relationships were studied.The reaction degree of fly ash,non-evaporable water content and the pH value in pore solution were calculated to reveal the mechanical property.The results indicate that as the curing age increases,the peak compressive strength,peak compressive strain and ultimate tensile strength of Eco-HDCC increase.However,the ultimate compressive strain and ultimate tensile strain of Eco-HDCC decrease with the increase in curing age.Besides,as the curing age increases,the reaction degree of fly ash and non-evaporable water content in Eco-HDCC increase,while the pH value in the pore solution of Eco-HDCC decreases.Finally,the simplified compressive and tensile stress-strain constitutive relationship models of Eco-HDCC with a curing age of 28 d were suggested for the structure design safety.

Effect of strain rate and water-to-cement ratio on compressive mechanical behavior of cement mortar

Effects of strain rate and water-to-cement ratio on the dynamic compressive mechanical behavior of cement mortar are investigated by split Hopkinson pressure bar(SHPB) tests. 124 specimens are subjected to dynamic uniaxial compressive loadings.Strain rate sensitivity of the materials is measured in terms of failure modes, stress-strain curves, compressive strength, dynamic increase factor(DIF) and critical strain at peak stress. A significant change in the stress-strain response of the materials with each order of magnitude increase in strain rate is clearly seen from test results. The slope of the stress-strain curve after peak value for low water-to-cement ratio is steeper than that of high water-to-cement ratio mortar. The compressive strength increases with increasing strain rate. With increase in strain rate, the dynamic increase factor(DIF) increases. However, this increase in DIF with increase in strain rate does not appear to be a function of the water-to-cement ratio. The critical compressive strain increases with the strain rate.

Compression behavior of 316L lattice structures produced by indirect additive manufacturing

As a new type of lightweight structure,metallic lattice structure has higher stiffness and strength to weight ratio.To freely obtain 316L lattice structures with designed cell structure and adjustable porosity,additive manufacturing combined with investment casting was conducted to fabricate the 316L lattice structures with Kelvin cell.The compression simulation of 316L lattice structures with different porosities was carried out by using the finite element method.The numerical simulation results were verified by compression experiment,and the simulated results were consistent with the compression tests.The compressive mechanical properties of 316L lattice structures are directly related to porosity and independent of strut diameters.The 316L lattice structures with Kelvin cell have a smooth stress-strain curve and obvious plastic platform,and the hump stress-strain curves are avoided.

Synthesis and compressive fracture behavior of a CuZr-based bulk amorphous alloy with Ti addition

Cu46Zr46A14.8Ti3.2 bulk metallic glass （BMG） was successfully synthesized by copper-mold casting and the mechanical properties at room temperature were measured by compression tests. The structure and thermal characteristics were analyzed by XRD and DSC, and the fracture surface morphology was examined by SEM. The glassy alloy with 4 mm in diameter shows an high fracture strength of 1 960 MPa, with an improvement of about 20% compared to the ultimate compression fracture strength of the Cu46Zr46A18 BMG, which suggests that the Ti addition improves the compression fracture strength. The different degrees of the adiabatic heating induce four types of fracture features： a vein-like structure, an elongated and striated vein pattern, melting and smooth regions. The elongated and striated vein patterns as well as the melting region show that enormous strain energy is released, which causes significant adiabatic heating. Furthernaore, many micro-cracks observed in the smooth region are caused by the strong shear force. In addition, the strong shear force leads to many shear bands as well as the melting in the lateral surface.

High-temperature Compressive Performance of Mg Alloy Foams Coated with Ni-P Layer

Mg/Ni hybrid foams were fabricated by the electroless method.The Ni-P(Nickel-Phosphorous)coatings were deposited on the surface of closed-cell Mg alloy foams.The composition,microstructure and phases of the Ni-P coatings were characterized by scanning electron microscopy(SEM),energy-dispersive X-ray spectroscopy(EDS)and X-ray diffraction(XRD),respectively.The compressive tests were performed on the Mg/Ni hybrid foams at 400℃using the Mg alloy foams as a reference.The experimental results show that the yield strength,plateau stress and energy absorption capacity of the closed-cell Mg alloy foams at high temperature were improved by the Ni-P coating.And there are four main modes for the Mg/Ni hybrid foam failure at 400℃,i e,shearing in cell wall,bending in cell edge,shedding and cracking in Ni-P coating.