Impact Deformation Research Articles

Effect of hydrogen embrittlement on the safety assessment of low-strength hydrogen transmission pipeline

Currently, no systematic approach exists for the safety assessment method of hydrogen transmission low-strength pipeline, it is necessary to study the effect of hydrogen embrittlement (HE) on the method of failure assessment diagram (FAD) for the defective pipe. The hydrogen charging experiments of tensile and Charpy impact specimens for the L245 pipe steel were carried out with charging time of 0, 30, 90, and 120 h, and then the tensile and Charpy impact tests were immediately conducted. The HE indexes of tensile and Charpy impact properties were presented to quantitatively analyze the effect of HE under tensile and impact deformation processes. Subsequently, the FAD method coupled with the effect of HE was investigated to analyze the difference in the safety assessment method between hydrogen and non-hydrogen environments. Finally, the fracture morphology of tensile and Charpy impact specimens was observed to analyze the responses of microscopic fracture modes between hydrogen and non-hydrogen environments. The results show that the effect of HE on the tensile properties of the base material is more sensitive than that of the weld joint. The FAC with the effect of HE for safety assessment of defective pipes shrinks by reducing the safe zone. The decrease ratio of safety factors affected by HE presents an increasing tendency as the increase of crack depth while showing a decreasing tendency as the increase of internal pressure.

Prediction method of impact deformation mode based on multimodal fusion with point cloud sequences: Applied to thin-walled structures

One of the challenges in solving the structural crashworthiness optimisation problem under impact deformation constraints is to construct an efficient and concise representation method for structural impact deformation. This representation method is expected to include as much information about the structural impact deformation as possible and be computable through numerical simulation, so that it can be combined with the structural impact process. Based on the comparison among several methods, a representation form is proposed using point cloud sequences of finite element nodes in the structural impact process, and the relevant construction method for the point cloud dataset is provided. The dataset includes point clouds derived from the impact deformation and the initial finite element node, structural design variables, and crashworthiness response values of the thin-walled tube during impact process. Based on the constructed dataset, a multi-modal fusion prediction method for the impact process of thin-walled structures is proposed to ensure the efficiency and reliability of crashworthiness prediction with unstructured data. The surrogate model takes structural design variables and initial deformation representations as inputs while impact deformation representations and crashworthiness responses as outputs. The relative errors of the surrogate model's predictions for the crashworthiness responses and impact deformation point cloud are within 5 % of the numerical results. Moreover, the computational speed is 8169 times faster than finite element simulation, ensuring solution accuracy while significantly improving the efficiency of structural crashworthiness prediction. Additionally, the robustness of the surrogate model and the importance of each module are verified and tested through experimental design, providing reference for further improvements to the surrogate model.

Mechanical performance study of basalt-polyethylene fiber reinforced concrete under dynamic compressive loading

In order to enhance concrete's impact resistance, this study investigates the effects of single basalt fiber and basalt-polyethylene hybrid fiber on concrete through split Hopkinson pressure bar (SHPB) tests, emphasizing their significance in engineering applications. A comparative analysis of the failure modes, dynamic compressive strength, dynamic compressive toughness, and dynamic growth factor of specimens was conducted under different strain rates and polyethylene fiber volume fractions. The study considered concrete damage, strain rate effect, and the toughening effect of fibers, introducing the damage factor, and establishing a dynamic damage constitutive model for fiber-reinforced concrete. The results showed that basalt-polyethylene fiber reinforced concrete (BPFRC) exhibited better impact resistance and deformation capability. There were improvements observed in dynamic compressive strength, dynamic compressive toughness, and dynamic growth factor. The addition of basalt fiber (BF) and polyethylene fiber (PE) played a buffering role in inhibiting crack propagation and slowing down the damage process. The optimum PE volume fraction for dynamic compressive strength was 0.1% at a strain rate of 60 s−1, 0.15% at a strain rate of 95 s−1, and 0.05% at a strain rate of 120 s−1, all with a BF volume fraction of 0.25%. The optimum fiber volume fractions for dynamic compressive toughness and dynamic peak toughness were consistent, both at 0.25% BF and 0.1% PE. The established dynamic damage constitutive model for fiber-reinforced concrete can effectively describe the impact resistance performance of BPFRC, and the experimental curves fit well with the constitutive curves. Furthermore, it was observed that BF acted as macrofibers, bridging to restrain the post-hardening cracking of concrete, while PE acted as microfibers, inhibiting the propagation of plastic cracks, reducing internal defects in concrete, and enhancing the ductility and toughness of concrete. Consequently, BPFRC holds significant potential value in engineering applications.

Theoretical Analysis of Plastic Behavior of Sandwich Beam with Metal Foam under Repeated Impacts

The phenomenon of repeated impacts on engineering structures is very common, especially in naval and ocean engineering. When marine structures are subjected to repeated impact loadings, deformation and damage will accumulate as the impact number increases, resulting in the failure and damage of the structures, even causing serious accidents. Based on the rigid-plastic assumption, a theoretical model is established to analyze the plastic mechanical behavior of metal foam sandwich beams (MFSBs) suffering from repeated impacts, in which the membrane factor method (MFM) is applied to derive analytical solutions for the plastic responses of MFSBs. The theoretical predictions agree well with the results of impact tests and numerical simulations, indicating that the theoretical model is accurate and reliable. In addition, the dynamic responses of MFSBs are analyzed based on the MFM, and the effects of the core strength and the face thickness on the deflection responses are determined. The results show that the dimensionless permanent deflection of MFSBs is sensitive to the core strength ratio and the face thickness ratio, and as the core strength ratio or the face thickness ratio increases, the dimensionless permanent deflection decreases gradually in an exponential form. In addition, the influence of the core strength ratio and face thickness ratio becomes more significant as the impact number increases. The proposed theoretical method can provide a theoretical reference and technical support for the design of metal foam sandwich structures with improved impact resistance under repeated impact loadings.

Multi-objective optimization of additive manufactured functionally graded lattice structures under impact

A multi-objective optimization procedure to effectively design gradient lattice structures under dynamic loading is presented. It aims both at maximized energy absorption characteristics and a lightweight design. The reduction of the peak crushing force and a maximized specific energy absorption are simultaneously optimized. Design variables like the relative density and density gradient of the lattice structure are investigated, considering different topologies of the lattice unit cells. To model and simulate the lattice structures efficiently, a simplified beam-based simulation finite element model is introduced and validated against experimental tests. They cover the range from dynamic equilibrium up to compaction wave propagation as impact deformation phenomena. Based on large numbers of simulations, an artificial neural network is used to predict the energy absorbing characteristics for the given design parameters and to find the optimal configuration of the lattice structures. The neural network is trained using a multi response adaptive sampling algorithm allowing parallel simulation with automatically generated finite element models during each iteration step. Subsequently, a multi-objective genetic algorithm is used to find optimal combinations of the design parameters of lattice structures under different impact velocities and cell topologies.

Evaluating constitutive models of smoothed particle hydrodynamics for bird-strike simulation

In this paper, the response of different bird constitutive models under high-speed impact was analysed by numerical methods, and the accuracy of the bird models was evaluated based on the experiments of bird impact on titanium alloy plates. Firstly, the finite element software LS-DYNA was used to build the model of bird impact on a titanium alloy plate. The impact deformation of the plate was investigated, and the numerical results were compared with the experiments. Next, the time histories of kinetic energy and impact force for different models were analysed. Finally, the deformation of the birds during the impact was compared. The results show that the hydrodynamic fluidic material model has the advantage in predicting the displacement of the plate, especially at the impact velocity of 180 m/s, and the predicted displacement results match the experiment the best. The kinetic energy of the four material models can reflect the displacement results. The kinetic energy of the hydrodynamic fluidic material model decays slowly, with the most remaining kinetic energy and the largest plate displacement; the kinetic energy of the elastic-plastic model decays fastest, with the minor remaining kinetic energy and the smallest plate displacement.

A review of armour's use of composite materials

Composites with a laminated structure come from stacking ceramic and metal in a particular order. Because of their high strength and hardness, low density of ceramics, and extraordinary flexibility, metals can be used as bulletproof armour. The bullet anti-penetration system includes a ceramic screen that slows down the projectile and splits it up and a metal backplate that plastically deforms to absorb the projectile's kinetic energy. Laminates have several downsides, including weak interface bonding, a tendency for tip cracks due to increased internal stress, and a jarring difference between the metal and ceramic properties. Crack migration and propagation can cause abrupt changes in material characteristics at the ceramic–metal contact. A drop between the ceramic panel and metal backplate can be easily triggered when a ceramic panel is impacted, as cracks form in the interlayer. In this area, the interface bonding strength is still inadequate. In this review, we looked at the meshless smoothed-particle hydrodynamic method for high-velocity impact and massive deformation, the finite-element simulations of interface impact resistance and the first-principles predictions of interface strength. The paper concludes with numerous suggestions for future improvement: Further study is required on ceramic toughening to increase the compatibility of ceramic panels and metal backplates, the performance transition between ceramic and metal, and the reliability of ceramic–metal laminated materials. It is critical to study ways to strengthen metals. More multiscale research using methods like the phase-field method, finite element analysis, and first-principles computations, focusing on how to mix these techniques naturally and successfully, is needed to reinforce metals by introducing nano-phases into metal matrix composites while still retaining the metal's ductility. The latest study that emphasises the potential advantages of hybrid materials, specifically the combination of aramid and kenaf fibres, highlights a notable progression in the domain of armour technology.

Research on In-Plane Deformation Performance of Rotating Honeycomb Structures.

Most natural materials have rotational and hierarchical properties, so they can show excellent mechanical properties such as shear resistance and impact resistance. In order to further improve the energy absorption characteristics of vibration absorbing structures, a new type of honeycomb structure with integral rotation and group rotation is designed and characterized. The effects of the geometrical parameters of rotation Angle on the impact deformation mode, stress response curve and energy absorption characteristics of the honeycomb structure are studied through numerical simulation and experimental design. The results show that the overall honeycomb performance of 15° is better than that of 0°, the specific energy absorption is the results show that the overall honeycomb performance of 15° is better than that of 0°, the specific energy absorption is increased by 6%, the bearing capacity is increased by 320 N, and the crushing force efficiency is increased by 2%. Compared with the whole cell and the group cell, the specific absorption energy increased by 35%, 73% and 71%. The results of this paper provide a new insight into the impact performance of monolithic and grouped rotating honeycomb structures, which is helpful for the results of this paper provide a new insight into the impact performance of monolithic and grouped rotating honeycomb structures, which is helpful for the optimization of crashworthiness structural design.

Impact dynamics and polarization mechanism of BaxSr1−xTiO3 particles reinforced polydimethylsiloxane composites

AbstractBaxSr1−xTiO3 (BST) ceramics have excellent performance of electromechanical conversion, however, the application of BST ceramics in the field of sensing is restricted by the brittle fracture, electromechanical failure, and collateral damage of BST under impact. In this article, unpolarized BST particles reinforced polydimethylsiloxane (PDMS) composites‐BST/PDMS with excellent mechanical properties, flexibility and flexoelectric coefficient have been prepared. Experimental study on the dynamic mechanical behavior and polarization characteristics of BST/PDMS composites under different impact velocity, element ratio and content of BST are carried out. Furthermore, the three‐phase model have been developed, based on that, impact deformation, stress behavior and polarization response have been investigated. The results show that, the duration of elastic deformation stage increases with increasing of BST content, but maximum stress decreases; time‐history curves of polarization voltage are approximately a “sine” function distribution, polarization voltages of Ba0.75Sr0.25TiO3/PDMS are higher than that of Ba0.25Sr0.75TiO3/PDMS; flexoelectric coefficient increases with increasing of BST content, and μzzzz is larger than that of μxxzz and μxzxz; addition of BST particle leads to greater strain gradient, and increases the polarization voltage of PDMS matrix; electric field at the interface increases due to the dielectric effect, which improves the ability of charge migration, voltage difference of 20% Ba0.75Sr0.25TiO3/80% PDMS caused by interfacial potential is smaller (about 9.3%) compared with 10% Ba0.75Sr0.25TiO3/90% PDMS. This work is significant for the development of flexible intelligent sensing materials.Highlights The mechanical behavior and polarization characteristics of BST/PDMS are studied. The polarization voltages of BST/PDMS (x = 0.75) are higher than BST/PDMS (x = 0.25). The flexoelectric coefficient increases with increasing of BST content.

Microstructural Study of Cold-Sprayed CoCrFeNiMn High Entropy Alloy

The rapid development of cold spraying technology for additive manufacturing of engineering components has made it a viable option for developing thick deposits from high-entropy alloys (HEAs). The microstructure of cold-sprayed CoCrFeNiMn deposit was investigated in this study using electron backscattered diffraction, scanning electron microscopy, and finite element analysis (FEA). The limited studies on the impact deformation behavior of the HEA during cold spraying, limiting our understanding of impact phenomena, and interactions between the HEA particles under ultra-high strain rate deformation motivated this study. From the microstructural characterization, heterogeneous microstructure appears to be formed in the cold-sprayed HEA deposit, comprising of equiaxed ultrafine grains at the particle–particle interfacial regions and coarse grains at the particle interiors. The FEA reveals large strain (> 250%) and temperature (> 90% of the alloy solidus temperature), mainly at the splat’s interfaces. Adiabatic shear instability and rotational dynamic recrystallization resulting from heat accumulation and high strain are believed to be responsible for these observations during the ultra-high strain rate deformation of the HEA. The large deformation and grain refinement experienced by the HEA resulted in greater deposit hardness when compared with the sprayed powder, with the nanohardness increasing from 1.16 GPa in the powder to 5.14 GPa in the deposit. This study explores and provides an understanding of the deformation behavior of the HEA and the resulting microstructure during cold spraying.

X-ray Diffraction Method in the Study of a Metal Surface Stress State Under Static and Impact Deformation

Study of the stress field in a plastic imprint and around it is of great practical importance. Processes similar to indentation are used in shot blasting to harden the surface of materials and generate compressive stresses in the surface layers. The purpose of this work was to study the change in the stress-strain state in the area of the plastic imprint with increasing load, in the transition from small to large deformations, as well as to study the change in stress at different strain rates.X-ray diffraction method was used to study the field of residual stresses generated on the surface of a plastically deformed region – in the zone of an imprint formed when a spherical indenter is pressed into the metal. An analysis of the change in the stress distribution with increasing load in the range of plastic imprint depths of 10–60 µm for steels and aluminum was made. Influence of the loading rate on the change in the values of residual stresses under normal contact of colliding bodies was studied. It is shown that the stress distribution has a complex character with areas of compression and tension of the metal and is determined by the ratio of the indentation depth to its diameter.The obtained experimental data make it possible to determine the choice of optimal modes of shot blasting, including for increasing the endurance limit of products.

SHPB experiments and FDM-DEM coupled simulations on calcareous sand under uniaxial to triaxial deformation

The impact behavior of sand is paramount to geotechnical and protective engineering. Although the one-dimensional impact responses of sand are extensively studied, the behavior of shear under impact loading remains poorly understood as the shear stresses in uniaxially compressed sand cannot attain the failure state. This paper reports the macroscopic responses of crushable calcareous sand under uniaxial to triaxial deformation by split Hopkinson pressure bar (SHPB) experiments. In addition, the mesoscopic mechanism is analyzed by coupled finite difference method (FDM) and discrete element method (DEM) numerical simulations. With an increasing lateral confined stiffness, the p-q curves exhibit a clockwise rotation, signifying a deviation of the stress path from the critical state line (CSL) during the transition from triaxial to uniaxial deformation, meanwhile the Mohr circle experiences a shift from intersecting to tangential contact with the failure line, indicating that shear failure occurs under triaxial deformation. The stress-strain relationships for both compression and shear exhibit four distinct regimes, the initial elastic stage mainly overcomes intergranular friction through particle rotation; the yield stage mainly compresses the skeleton by contribution of displacement; the hardening stage experiences critical particle breakage and then promotes particle displacement and rotation; and the unloading stage with strain softening caused by the asynchrony between impact loading and deformation. Both compressed and shear yield stress increases with an increasing confined stiffness, but the shear friction angle decreases. This indicates that the governing factor in triaxial compression under impact loading is the stress state rather than kinetic friction. Particle breakage in triaxial compression state tends to approach the splitting mode, while in uniaxial squeezing state it tends to approach the Mixed mode.

Determining the instantaneous bruising pattern in a sample potato tuber subjected to pendulum bob impact through finite element analysis

AbstractPotato bruising resulting from mechanical impact during production operations including harvest and postharvest is a significant concern within the potato production sector, leading to consumer complaints and economic losses. The detection of instantaneous internal bruising poses a particular challenge as it can progress over time during storage or transportation, making it difficult to identify immediately after external impact. This study aims to investigate the progression of bruising and accurately represent the instantaneous dynamic deformation behavior of potato tubers under four pendulum bob impact cases (pendulum arm angles of 30°, 45°, 60°, and 90°). To analyze the dynamic impact deformation characteristics of the tubers, solid modeling based on a reverse engineering approach and explicit dynamic engineering simulations were employed. The simulation results yielded valuable numerical data and visual representation of the deformation progression. The loading conditions considered in this study indicated that the maximum stress values, reaching 0.818 MPa at a pendulum arm angle of 90°, remained below the bio‐yield stress point of the tuber flesh (1.05 MPa) determined through experimental compression tests. Therefore, it was concluded that the impact did not cause permanent deformation (i.e., permanent bruising) in the tuber. However, the numerical analysis clearly demonstrated the sequence of stress occurrences, which is a key contributing factor to potential permanent bruising. In this regard, the bruising energy threshold of 318.314 mJ (R2: 0.96) was extrapolated. The numerical findings presented in this study can aid in evaluating the susceptibility of tuber samples to bruising. By employing nonlinear explicit dynamics simulations, this research contributes to the advancement of understanding complex deformation and bruising in solid agricultural products. Moreover, the application of these techniques holds significant industrial implications for enhancing the handling and transportation of agricultural produce.Practical applicationsThis research aims to tackle the challenge of accurately representing the immediate internal bruising pattern in potato tubers resulting from mechanical impact. Conventional methods, such as physical or analytical expressions, may not fully capture the distribution of bruising experienced by the tubers. To overcome this limitation, an engineering simulation approach is proposed to provide a more precise depiction of the instantaneous bruising pattern. By advancing the understanding of complex deformation and bruising in solid agricultural products, this research contributes to improving the efficiency and quality of agricultural production in the industry. Additionally, this study offers a step‐by‐step guide on how to conduct these simulations effectively.

The Impact Modeling and Experimental Verification of a Launch Vehicle with Crushing-Type Landing Gear

In order to investigate the landing process of a vertical landing reusable vehicle, a dynamic model with a complex nonlinear dissipative element is established based on the discrete impulse step approach, which includes a three-dimensional multi-impact model considering friction and material compliance, and a multistage aluminum honeycomb theoretical model. The normal two-stiffness spring model is adopted in the foot–ground impact model, two motion patterns (stick and slip) are considered on the tangential plane and the structural changes caused by buffering behavior are included, and the energy conversion during the impact follows the law of conservation of energy. The state transition method is used to solve the dynamic stability convergence problem of the vehicle under the coupling effect of impact and buffering deformation in the primary impulse space. Landing experiments on a scaled physical reusable vehicle prototype are conducted to demonstrate that the theoretical results exhibit good agreement with the experimental data.

Corrosion and Erosion Wear Behaviors of HVOF-Sprayed Fe-Based Amorphous Coatings on Dissolvable Mg-RE Alloy Substrates.

To suppress the corrosion and erosion wear of dissolvable magnesium alloy ball seats in wellbores, Fe-based amorphous coatings were deposited on dissolvable Mg-RE alloy substrates, and their microstructure, corrosion behavior, and erosion wear behavior were studied. The thickness of Fe-based amorphous coatings on dissolvable Mg-RE alloy substrates can reach 1000 μm without any cracks, and their porosity and amorphous contents are 0.79% and 86.8%, respectively. Although chloride ions will damage the compactness and protective efficacy of passive films, Fe-based amorphous coatings still maintain low corrosion current density (3.31 μA/cm2) and high pitting potential (1 VSCE) in 20 wt% KCl solution. Due to their higher hardness, the erosion wear resistance of Fe-based amorphous coatings is about 4.16 times higher than that of dissolvable Mg-RE alloy substrates when the impact angle is 30°. Moreover, the erosion rates of Fe-based amorphous coatings exhibit a nonlinear relationship with the impact angle, and the erosion rate reaches the highest value when the impact angle is 60°. The erosion wear mechanisms of Fe-based AMCs vary with the impact angles, including cutting, delamination, splat fracture, and deformation wear. This work can provide effective guidance for the corrosion and wear protection of plugging tools made from dissolvable magnesium alloy.

Multi-scale finite element analysis on the soft impact behavior of twill weave laminate

This work proposed an impact momentum flexibility (IMF) to precisely and concisely characterize the soft impact behavior of twill weave laminate based on multi-scale finite element analysis. A multi-scale finite element model taking into consideration the microstructure and properties of constituents is established for twill weave laminate. The equivalent properties of fiber tows and twill weave laminate are predicted by micro-scale model and meso-scale model, respectively. Then the soft impact behavior of the laminate is investigated by macro-scale model. The multi-scale model is validated on different scales by comparing the experimental and simulated results of quasi-static compression and soft impact. On this basis, the deformation and failure of the laminate under soft impact are analyzed. The soft impact response is categorized according to the damage morphology and impact velocity. Moreover, the IMF is proposed to depict the ability to resist soft impact deformation of the laminate, and can be further adopted to rank the soft impact property of different materials.

Experimental investigation into the transverse impact performance of high-strength circular CFST members

Both high-strength steel and high-strength concrete are gaining increasing use in the construction industry. At the same time, the benefits of composite construction are also being increasingly recognized and exploited. In the present study, high-strength steel and high-strength concrete are considered in combination in high-strength concrete-filled high-strength steel tubular (HSCFST) members, with a focus on their behaviour under transverse impact loading, resistance to which is important for resilient infrastructure. Tests on thirteen HSCFST specimens and six reference CFST specimens under drop weight impact loading are presented. Hot-finished high-strength S890 steel sections were employed for the outer tubes of the HSCFST specimens, while hot-finished S355 steel tubes were used for the reference CFST specimens. Two core concrete strengths of approximately 60 MPa and 100 MPa were considered. The instantaneous impact force and deformation histories of the specimens were recorded at high frequencies throughout the impact process. A single-degree-of-freedom (SDOF) model was developed and used to facilitate the analysis of the experimental results. The dynamic moment capacities of the test specimens were obtained using the developed SDOF model and a dynamic increase factor (Rd) was introduced to quantify the enhancement in moment capacity relative to the static values. The influence of the test parameters on the dynamic increase factors was then analysed. The test results indicated that Rd is positively correlated with the impact velocity and negatively correlated with the steel grade, steel ratio and specimen length, while being insensitive to the concrete strength.

Analysis of Heavy Motor Vehicle Chassis Frame with Different Materials Equipped with CNG Cylinders of Composite Materials Using CAE Tools

Abstract: The transport sector now has a significant impact on both the economies of developed and developing nations The frame, also known as the chassis, is the main part of the vehicle because it has the highest design stress. This is vehicle support as all components are only supported on the chassis. Using the chassis as a platform, the front and rear suspensions are connected without dropping. At the same time, it can also be used for sudden stops, bumpy roads, and high-speed driving. It has sufficient rigidity to withstand impact, deflection, bending, vibration and shape deformation caused by causes. Scientific data obtained from various studies to date, weight, stress and strength, deformation, etc. have proven to be ideal for many factors. This can be done by changing the section and material of the chassis frame. The material chosen for this project is AISI4130 for LPO 1613 CNG BS-IV OBDII Front Engine Bus for Delhi Integrated Intermodal Transport System (DIMTS). Create 3D models in CAE Solid-works and analyze them with ANSYS 19.2. Automotive composite CNG cylinders are the best combination of the latest technology using carbon fiber reinforced seamless aluminum inner liner

Dynamic tensile properties of geopolymer concrete and fibre reinforced geopolymer concrete

Geopolymer concrete (GPC) has attracted much attention over the past decades because it utilizes industry wastes and has outstanding mechanical properties. To improve its ductility and energy absorption capabilities, various types of fibres have been incorporated into GPC. This paper carries out an experimental study to quantify the dynamic tensile properties of GPC and fibre reinforced GPC (FR-GRC) with hooked-end steel fibre and polypropylene (PP) fibre. Both quasi-static and dynamic split-tensile tests are performed on plain GPC and FR-GPC covering strain rates of 10-5s−1 to 16 s−1. The addition of 0.5% volume content of steel and PP fibres is found to effectively improve the ductility of GPC at both static and dynamic states. Under quasi-static loading, the crack opening displacements reach about 0.15 mm for GPC, 9 mm for SGPC and 8 mm for PPGPC upon failure, and when subjected to impact loading, the crack-opening rate of GPC is higher than that of FR-GPC. Fibre stretching process after concrete crack till pull-out/fracture is observed which considerably contributes to the reduction of crack expansion and the enhancement of energy dissipation capacity of GPC, with enhancements reaching up to 33% for PPGPC and 94% for SGPC. The split-tensile properties of both plain GPC and FR-GPC are found to be sensitive to strain rate, while geopolymer with PP fibre shows a similar behaviour as plain geopolymer, and GPC with steel fibres appears to be less sensitive to strain rate effect. Empirical relations are proposed to correlate the dynamic increase factor (DIF) of tensile strength for GPC and FR-GPC with strain rate. Comparison between plain GPC and FR-GPC shows that fibres can absorb additional energy to improve the impact resistance and deformation capacities.

Comparative study on the effect of test temperature on tensile and charpy impact properties of Ti–5Al–1V–1Sn–1Zr-0.8Mo alloy

Impact toughness is a critical indicator to prevent catastrophic failure, especially at low service temperature. At present, most strategies to strengthen and toughen Ti alloys are proposed under the quasi-static tensile deformation condition. In fact, whether these strategies can be directly extended to improve impact toughness is still controversial due to the high loading rate and the existing of pre-notch during Charpy impact deformation condition. In this work, we found that, even though the yield strength and elongation of Ti–5Al–1V–1Sn–1Zr-0.8Mo alloy increase simultaneously with the decrease of test temperature under tensile deformation condition, the impact toughness still decreases gradually with the decreasing of deformation temperature under Charpy impact deformation condition. This phenomenon indicates that the successful strengthening and toughening strategies under quasi-static tensile deformation may fail under impact deformation. Finally, the reasons behind this phenomenon are explained based on the comparison of surface deformation morphologies under different deformation conditions, and the corresponding deformation mechanisms are established.