Impact Properties of Engineered Cementitious Composites with High Volume Fly Ash Using SHPB Test

The split Hopkinson pressure bar （SHPB） testing with diameter 40 mm was used to investigate the dynamic mechanical properties of engineered cementitious composites （ECCs） with different fly ash content. The basic properties including deformation, energy absorption capacity, strain-stress relationship and failure patterns were discussed. The ECCs showed strain-rate dependency and kept better plastic flow during impact process compared with reactive powder concrete （RPC） and concrete, but the critical compressive strength was lower than that of RPC and concrete. The bridging effect of PVA fiber and addition of fly ash can significantly improve the deformation and energy absorption capacities of ECCs. With the increase of fly ash content in ECCs, the static and dynamic compressive strength lowered and the dynamic increase factor enhanced. Therefore, to meet different engineering needs, the content of fly ash can be an important index to control the static and dynamic mechanical properties of ECCs.

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.

IMPACT PROPERTIES OF METALLOCENE - CATALYZED ETHYLENE-α-OLEFIN COPOLYMERS

The impact properties of two selected metallocene-catalyzed ethylene-butene copolymers and one conventionalcopolymer were evaluated using Izod impact test. It is found that the metallocene-catalyzed copolymer shows superior impactproperties. This result was explained on the basis of the more homogeneous inter-molecular composition distribution andnarrower molecular weight distribution, which leads to more homogeneous morphology with fewer defects. Stepwisecrystallization improves the impact properties, especially in the crack propagation process, to a large extent. This is due to thedecrease of entanglements by stepwise crystallization, which is advantageous for the chain slip and shear. The polymer withheterogeneous intra-molecular composition distribution exhibits a more evident improvement of impact properties understepwise crystallization.

THE IMPACT PROPERTIES OF HYBRID COMPOSITES

In this paper an experimental investigation on the impact behaviour of hybrid composites is conducted by instrumental Charpy impact test. The variation of impact strength and impact toughness index of C/K and C/G hybrid composites of different matrices with hybrid ratio and interface number is revealed. The dynamic hybrid effect is also investigated from different aspects. Meanwhile, the estimating model for impact strength is established and the estimated values are in good agreement with experimented ones. The hybrid effect coefficients based on different definitions are organically related by the model. This provides a basis for the further study of the impact constitutive equation of hybrid composites.

Comparative Study of Tensile and Charpy Impact Properties of X70 and X80 Linepipe Steels After Ultra Fast Cooling Processing

Ultra fast cooling（UFC） processing after hot deformation was conducted on X70 and X80 linepipe steels. Tensile and charpy impact properties of both steels have been investigated in this work. The results have shown that the mechanical properties satisfy all the standard requirements of the X70 and X80 steels. UFC results in a presence of microstructure containing quasi polygonal（QF）, acicular ferrite（AF） and granular bainite（GB）. The alloying elements and UFC enhance the strengthening contribution caused by solid solution, dispersion, dislocation and precipitation strengthening. The size and distribution of precipitates in the linepipe steels are fine and dispersed. MA is also homogeneously dispersed due to UFC. Average grain size in the X80 steel is finer than that in the X70 steel. The volume fractions of secondary phases in the X80 steel are greater than those in the X70 steel. The X80 steel remains finer and more dispersed precipitates compared to the X70 steel. As a result, the tensile properties of X80 steel are higher than those of X70 steel. The Charpy absorbed energies of X70 and X80 steels at-10 ℃ reached 436 and 460 J, respectively. They reached 433 and 461 J at-15 ℃, respectively. This is mainly attributed to the presence of larger amounts of AFs in the X80 steel. A microstructure of AF for the X80 steel results in combining high strength and high toughness.

Improvement of impact properties of Al-Si-Mg alloy via solution treatment and joint modification with Sr and La

An effort to obtain superior impact properties for Al-7Si-0.35 Mg alloy is presented,where modification with 0.02 wt% Sr and 0.1 wt% La as well as solution treatment was jointly employed.The samples were solution treated at 535℃ for 15 min to 12 h.The microstructure,fracture mechanism,and their correlation with the impact properties of the alloy were studied in detail mainly through optical microscopy(OM),scanning electron microscopy(SEM) and oscillography impact test.The results show that the addition of Sr and La refined the eutectic Si particles significantly from~ 2.05 μm(modified with Sr alone) to~ 0.75 μm in as-cast microstructure,leading to a very homogeneous distribution of spheroidized Si particles in the alloy solution treated at 535℃ for 8 h.The alloy exhibits excellent impact toughness up to 75 J·cm^(-2),which is much higher than the maximum impact toughness of the alloys modified by Sr alone(~ 46 J·cm^(-2)).The major reason for this remarkable increase in the impact property is the dramatic increase in crack initiation energy.The dispersoid-free zones(DFZs)near the eutectic regions mainly consist of the ductile Al-matrix,which exhibits excellent ductility.The ductile Al-matrix of the DFZs hinders the crack propagation,resulting in a significant increase in crack propagation energy.

Effects of Nb Addition on Charpy Impact Properties of TiVTa Refractory High‑Entropy Alloy

In the present study,the effects of Nb addition on Charpy impact properties of TiVTa refractory high-entropy alloy with high strength-ductility trade-off were systematically studied by using the instrumented Charpy impact testing machine.The experimental results showed that the impact toughness was remarkably improved by Nb addition in TiVTa to form TiVTaNb alloy.The crack initiation energy and propagation energy of TiVTaNb were 67.3%and 24.9%higher than that of TiVTa,indicating that Nb addition simultaneously reinforced the resistance to crack initiation and propagation.The impact fracture of TiVTaNb exhibited larger bending degree of shear lips,deeper dimples and more secondary cracks which effectively dissipated more impact energy.The deformation mechanism of TiVTa alloy was dominated by dislocation activities.While in TiVTaNb,the deformation mechanism was synergized by dislocation activities and deformation twinning,which were the main contributors for the improved impact properties and the stronger crack resistance of TiVTaNb alloy under impact loading.

Comparison of Impact Properties for Carbon and Low Alloy Steels

The impact properties of hot rolled carbon steel （used for the manufacture of reinforcement steel bars） and the quenched ＆ tempered （Q＆T） low alloy steel （used in the pressure vessel industry） were determined. The microstructure of the hot rolled carbon steel contained ferrite/pearlite phases, while that of the quenched and tempered low alloy steel contained bainite structure. Impact properties were determined for both steels by instrumented impact testing at temperatures between -150 and 200℃. The impact properties comprised total impact energy, ductile to brittle transition temperature, crack initiation and propagation energy, brittleness transition temperature and cleavage fracture stress. The Q＆T low alloy steel displayed much higher resistance to ductile fracture at high test temperatures, while its resistance to brittle fracture at low test temperatures was a little higher than that of the hot rolled carbon steel. The results were discussed in relation to the difference in the chemical composition and microstructure for the two steels.

Microstructure and impact mechanical properties of multi-layer and multi-pass TIG welded joints of Al-Zn-Mg alloy plates

The microstructure and mechanical properties of multi-layer multi-pass TIG welded joints of Al-Zn-Mg alloy plates were studied.The phase constituent and microstructure of different regions of the welded joints were characterized by scanning electron microscopy(SEM),X-ray diffraction(XRD),transmission electron microscopy(TEM)and energy disperse spectrum(EDS),while the mechanical properties were evaluated according to the impact test.A dispersively distributed spherical and needle-likeη(MgZn2)phase was obtained in the welding seam.The phase composition of the heat-affected zone(HAZ)wasα(Al)+η(MgZn2)+Al6Mn,and there were a large number of dispersively precipitated nanoscale particles.The welded joint zone had the highest impact toughness as compared with the other parts of the joint.The MgZn2 phase in the weld zone contributed to the improved toughness of the joint.Al2 MgCu phase in HAZ was proven to act as a crack source during fracture.

Effect of Autogenous Arc Welding Processes on Tensile and Impact Properties of Ferritic Stainless Steel Joints

The effect of autogeneous arc welding processes on tensile and impact properties of ferritic stainless steel conformed to AISI 409M grade is studied. Rolled plates of 4 mm thickness have been used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure, and fracture surface morphology of continuous current gas tungsten arc welding （CCGTAW）, pulsed current gas tungsten arc welding （PCGTAW）, and plasma arc welding （PAW） joints are evaluated and the results are compared. It is found that the PAW joints of ferritic stainless steel show superior tensile and impact properties when compared with CCG-TAW and PCGTAW joints, and this is mainly due to lower heat input, finer fusion zone grain diameter, and higher fusion zone hardness.

Impact Wear Properties of Metal-Plastic Multilayer Composites Filled with Glass Fiber Treated with Rare Earth Element Surface Modifier

The friction and wear properties of metal-plastic multilayer composites filled with glass fiber, which is treated with rare earth element surface modifier, under impact load and dry friction conditions were investigated. Experimental results show that the metal-plastic multilayer composite filled with glass fiber exhibits excellent friction and impact wear properties when using rare earth elements as surface modifier for the surface treatment of glass fiber.

Effect of Welding Processes on Tensile and Impact Properties,Hardness and Microstructure of AISI 409M Ferritic Stainless Joints Fabricated by Duplex Stainless Steel Filler Metal

The effect of welding processes such as shielded metal arc welding, gas metal arc welding and gas tungsten arc welding on tensile and impact properties of the ferritic stainless steel conforming to AISI 409M grade is studied. Rolled plates of 4 mm thickness were used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure and fracture surface morphology of the welded joints have been evaluated and the results are compared. From this investigatio.n, it is found that gas tungsten arc welded joints of ferritic stainless steel have superior tensile and impact properties compared with shielded metal arc and gas metal arc welded joints and this is mainly due to the presence of finer grains in fusion zone and heat affected zone.

Impact vibration properties of locally resonant fluid-conveying pipes

Fluid-conveying pipe systems are widely used in various equipments to transport matter and energy.Due to the fluid–structure interaction effect,the fluid acting on the pipe wall is easy to produce strong vibration and noise,which have a serious influence on the safety and concealment of the equipment.Based on the theory of phononic crystals,this paper studies the vibration transfer properties of a locally resonant(LR)pipe under the condition of fluid–structure interaction.The band structure and the vibration transfer properties of a finite periodic pipe are obtained by the transfer matrix method.Further,the different impact excitation and fluid–structure interaction effect on the frequency range of vibration attenuation properties of the LR pipe are mainly considered and calculated by the finite element model.The results show that the existence of a low-frequency vibration bandgap in the LR pipe can effectively suppress the vibration propagation under external impact and fluid impact excitation,and the vibration reduction frequency range is near the bandgap under the fluid–structure interaction effect.Finally,the pipe impact experiment was performed to verify the effective attenuation of the LR structure to the impact excitation,and to validate the finite element model.The research results provide a technical reference for the vibration control of the fluid-conveying pipe systems that need to consider blast load and fluid impact.

Effects of cryogenic temperature on tensile and impact properties in a medium-entropy VCoNi alloy

Multi-principal element alloys usually exhibit outstanding strength and toughness at cryogenic temperatures,especially in CrMnFeCoNi and CrCoNi alloys.These remarkable cryogenic properties are attributed to the occurrence of deformation twins,and it is envisaged that a reduced stacking fault energy(SFE)transforms the deformation mechanisms into advantageous properties at cryogenic temperatures.A recently reported high-strength VCoNi alloy is expected to exhibit further notable cryogenic properties.However,no attempt has been made to investigate the cryogenic properties in detail as well as the underlying deformation mechanisms.Here,the effects of cryogenic temperature on the tensile and impact properties are investigated,and the underlying mechanisms determining those properties are revealed in terms of the temperature dependence of the yield strength and deformation mechanism.Both the strength and ductility were enhanced at 77 K compared to 298 K,while the Charpy impact toughness gradually decreased with temperature.The planar dislocation glides remained unchanged at 77 K in contrast to the CrMnFeCoNi and CrCoNi alloys resulting in a relatively constant and slightly increasing SFE as the temperature decreased,which is confirmed via ab initio simulations.However,the deformation localization near the grain boundaries at 298 K changed into a homogeneous distribution throughout the whole grains at 77 K,leading to a highly sustained strain hardening rate.The reduced impact toughness is directly related to the decreased plastic zone size,which is due to the reduced dislocation width and significant temperature dependence of the yield strength.

Impact of Surface Passivation on the Electronic Structure and Optical Properties of the Si1-xGex Nanowires

The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly： the band gap widths and types （direct or indirect） of the Si1-xGe, NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si1-x Gex NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si1-xGex NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.

Study of the Diffusion Behavior of Seawater Absorption in Multi-Walled Carbon Nanotubes/Halloysite Nanotubes Hybrid Nanofillers Modified Epoxy-Based Glass/Carbon Fiber Composites

In the maritime industry, cost-effective and lightweight Fiber Reinforced Polymer (FRP) composites offer excellent mechanical properties, design flexibility, and corrosion resistance. However, their reliability in harsh seawater conditions is a concern. Researchers address this by exploring three approaches: coating fiber surfaces, hybridizing fibers and matrices with or without nanofillers, and interply rearrangement. This study focuses on evaluating the synergistic effects of interply rearrangement of glass/carbon fibers and hybrid nanofillers, specifically Multi-walled carbon nanotubes (MWCNT) and Halloysite nanotubes (HNT). The aim is to enhance impact properties by minimizing moisture absorption. Hybrid nanocomposites with equal-weight proportions of two nanofillers: 0 wt.%, 1 wt.%, and 2 wt.% were exposed to seawater for 90 days. Experimental data was subjected to modelling through the application of Predictive Fick’s Law. The study found that the hybrid composite containing 2 wt.% hybrid nanofillers exhibited a 22.10% increase in impact performance compared to non-modified counterparts. After 90 days of seawater aging, the material exhibited enhanced resistance to moisture absorption (15.74%) and minimal reduction in impact strength (8.52%) compared to its dry strength, with lower diffusion coefficients.

Dynamic Response of RPC-Filled Steel Tubular Columns with High Load Carrying Capacity Under Axial Impact Loading

Experimental investigation into impact-resistant behavior of reactive powder concrete (RPC)-filled steel tubular columns was conducted,and dynamic response of the columns under axial impact loading was studied by means of numerical simulation method.Increase coefficient of load carrying capacity and ratio of load carrying capacity between steel tube and RPC core of col-umns were obtained.

Microstructure and properties of laser-arc hybrid welding of high-strength low-alloy steel

Laser-arc hybrid welding has the characteristics of optimal surface formation and greater penetration;it is extensively used in the welding of plates of medium thickness.However, for hybrid welding of lasers, the welding seam cooling rate is rapid;thus, the welding seam has a higher tendency to significantly harden, which has a negative impact on the weld quality of the high-strength low-alloy(HSLA) steel plates of medium thickness.In this study, laser-arc hybrid welding is performed on the BG890 QL HSLA steel produced by Baoshan Iron & Steel Co.,Ltd.,and the quenching tendency of the welded structure is examined.The results demonstrate that the specific growth direction of the columnar crystal structure of the laser-arc hybrid welded joint is obvious.However, at the center and top of the welded seam, there are equiaxed crystals.The impact properties at room temperature and-40 ℃ of the weld area are 58.0 J and 40.0 J,respectively, and those of the heat-affected zone(HAZ) are 147.0 J and 66.5 J,respectively.The impact performance can meet these requirements.Laser-arc hybrid welding of HSLA steel can yield strong and durable welds and the HAZ structure to meet the requirements of engineering applications.

Effect of RE Modification and Heat Treatment on Impact Fatigue Property of a Wear Resistant White Cast Iron

The morphology of carbides, as well as the generation and propagation of fatigue cracks in a wear resistant white cast iron after impact fatigue test were observed by means of optical microscope and SEM, and the relationship among the content of RE (rare earths) in the wear resistant white cast iron and the heating temperature as well as the length and propagation speed of the fatigue cracks were determined. Based on the obtained results, the effect of RE modification and heat treatment on the impact fatigue property was further studied. Experimental results show that addition of RE can defer the time required for the generation of fatigue cracks, reduce their propagation speed and increase the impact fatigue resistance. The aforesaid effect is more noticeable in case of combined RE modification with heat treatment, which can be attributed to the variation in morphology and the distribution of the eutectic carbide network.

Effects of Temperature Induced Thermal Expansion and Oxidation on the Charpy Impact Property of C/C Composites

C/C composites are the emerging materials of choice for aero-engine hot-end components that will bear impact loading in thermal-oxidizing environments. For the components run for extended periods, the safe operation of components depends on how to evaluate damages under a dynamic load. In this study, Charpy impact tests at a temperature range of 25 to l 200 ＂C were carried out on C/C composites to verify the effects of temperature induced thermal expansion and oxidation on their impact performance. Below 800 ℃, oxidation was negligible and composites expanding played a leading role, resulting in the remarkable increase in fiber/ matrix interface strength and impact energy. However, when the temperature was above 800 ℃, the release of CO or CO2 due to oxidation resulted in a lower impact energy.