Dynamic Compression Tests Research Articles

Characterization of Ta-Ni-Al energetic structural material fabricated by explosive consolidation

Multi-element intermetallic energetic structural materials (ESMs) can be applied as reactive fragment, reactive shell and reactive shaped charge. As typical of intermetallics ESMs, Ni-Al ESMs have been heavily studied. However, the low density limits its application. This work proposed to improve the performance of Ni-Al ESMs by adding Ta. The nearly fully dense Ta-Ni-Al ESMs with a molar ratio 4:3:3 was successfully fabricated by explosive consolidation. The density was high up to 10.52 g/cm3 (98.3% theoretical maximum density). The heat treatment was used to further improve the performance of the Ta-Ni-Al ESMs. The microstructure characteristics were analyzed by scanning electron microscopy, X-ray diffraction and transmission electron microscope. The mechanical properties, reaction and impact-induced energy release have been systematically studied. Firstly, quasi-static and dynamic compression tests were conducted to analyze the mechanical properties of the sample before and after heat treatment. Secondly, the reaction characteristics in different atmospheres were discussed by differential scanning calorimetry and thermogravimetric analysis. The effect of the additive Ta was concerned. Furthermore, Impact-induced energy release tests on the Ta-Ni-Al ESMs were performed to understand the energy release properties. Based on these tests, the characterization of Ta-Ni-Al ESMs fabricated by explosive consolidation was obtained. There was no intermetallic formed in explosive consolidated samples. After the heat treatment, Ta-Ni-Al ESMs have good plasticity and strain rate effect. Meanwhile, under high impact velocity, the impact-induced energy release capability of Ta-Ni-Al ESMs was equivalent to Ni-Al ESMs.

Experimental Study on Dynamic Compressive Behaviors of Sand under Passive Confining Pressure.

Dynamic compressive tests of sand under passive confining pressure were carried out using a Split Hopkinson Pressure Bar (SHPB) setup. The dynamic response, energy dissipation and particle-breaking behaviors of sand subjected to high-speed impact were investigated. Sand specimens with moisture contents of 0%, 2%, 4%, 8%, 10% and 12% and relative densities of 0.1, 0.5 and 0.9 were prepared. The variation in the strain rate was controlled between 90 s−1 and 500 s−1. The specimens were confined in a designed sleeve to create passive confining pressure. The experimental results show that the sand specimens were extremely sensitive to the strain rate. When the strain rate was less than 400 s−1, the stress and strain of the specimens increased with the increase in the strain rate but decreased when the strain rate exceeded 400 s−1. The peak strain and peak stress increased with the increase in the relative density. Particle breakage was aggravated with the strain-rate increase. Compared with the specimen without water, the relative breakage rate of the specimen with a moisture content of 12% decreased by 30.53% when the strain rate was about 95 s−1 and by 25.44% when the strain rate was about 460 s−1. The analysis of energy dissipation revealed the essential cause of sand destruction. The specific energy absorption rate increased with the increases in the initial relative density and moisture content.

Establishment of the Corner Correlation Method and Its Application in Rock Dynamic Test

After combining the corner extraction method with the digital image correlation method, a new algorithm called the corner correlation method (CCM) was proposed, realizing a high-precision measurement for the displacement field and strain field on the surface of the specimen. It is applicable to the model with complex damage on the calculated surface. The errors of cross-crack speckle pattern and corner pattern are compared, and it was concluded that the errors of corner pattern of transverse and longitudinal cracks are less than that of the speckle pattern. The calculation accuracy of the corner correlation method is evaluated and verified by numerical simulation, static tensile test and dynamic uniaxial compression test respectively. It was found that the calculation accuracy was the highest with the Newton iteration method. The displacement calculation accuracy is about 0.01 pixels and the resolution of the measurement system for the strain test was on the order of 10−4 under dynamic load.

Effects of Accumulated Damage on the Dynamic Properties of Coal Measures Sandstone

The coupling effect of accumulated damage and impact load substantially affects the integrity of the surrounding rock structure in deep coal mining engineering, which has inhibited safe and effective coal mining. Therefore, dynamic compression tests were performed on coal measures sandstone specimens with accumulated damage using the SHPB device. The effects of a high strain rate and accumulated damage on the sandstone’s mechanical behavior and damage evolution were investigated. The results reveal that accumulated damage has a considerable impact on specimen stress–strain curves and lowers dynamic compressive strength and deformation modulus substantially. The sandstone failure mode looks to be shear failure from a macroscopic perspective, while it appears to be intergranular fracture between the mineral particles from a microscopic perspective. The macroscopic and microscopic failure mechanisms of the sandstone specimens likewise conformed to the energy absorption law. The accumulated damage factor and the accumulated damage correction coefficient were presented in order to construct a statistical damage constitutive model of rocks based on the Weibull distribution. This model provides a decent description of the effects of accumulated damage and the strain rate on sandstone’s mechanical behavior, with parameters that are all of evident physical significance.

Dynamic Mechanical Properties of TC11 Titanium Alloys Fabricated by Wire Arc Additive Manufacturing.

To study the compressive mechanical properties and failure modes of TC11 titanium alloy fabricated by wire arc additive manufacturing (WAAM) technology in a large strain rate range at room temperature, the quasi-static and dynamic compression tests were carried out. In addition, optical microscopy (OM) and scanning electron microscopy (SEM) were employed to observe the metallographic structure and fracture morphology, respectively. The stress–strain curves in the range of 0.001 s−1–4000 s−1, original and post-deformation microstructures, macroscopic damage patterns, and microscopic fracture morphology were obtained at two different loading directions, including the scanning and deposition directions, respectively. In uniaxial compression experiments, the material showed little difference in mechanical properties between the scanning and deposition directions, exhibiting a strain rate strengthening effect. However, the strain rate sensitivity of the material under quasi-static loading conditions is much less than that under dynamic loading conditions. In addition, combining the stress–strain curve with the fracture morphology analysis, the plasticity in the scanning direction is better than in the deposition direction. Based on the experimental results, a modified Johnson–Cook (JC) constitutive model considering strain rate sensitivity and the effect of strain rate on strain hardening was proposed, and the parameters were determined using a Multiple Population Genetic Algorithm (MPGA). The obtained constitutive model is in good agreement with the experimental data, which can provide a reference for the engineering numerical calculation of TC11 titanium alloy for WAAM. This study also provides a fundamental databank for the application and design of WAAM TC11 alloy in the manufacturing of large and complex structural parts.

Effects of microstructure on mechanical and energy release properties of Ni–Al energetic structural materials

Ni–Al energetic structural materials (ESMs) has been widely applied in defense field, because of its good mechanical and energy release properties. The effects of the microstructure on mechanical and energy release properties of ESMs are not well understood. In this study, by designing the particle size Ni:Al = 1 μm:25 μm and Ni:Al = 20 μm:25 μm, two kinds of samples, Ni continuous phase (Nicp) and Al continuous phase (Alcp), were prepared by explosive consolidation. The microstructure characteristics were analyzed by scanning electron microscopy, electron backscatter diffraction, and transmission electron microscope. Quasi-static and dynamic compression tests were also conducted to analyze the mechanical properties. It showed that the Nicp ESMs had higher quasi-static compressive strength of 325 MPa and fracture strain of 21.3%, compared with the Alcp ESMs having the strength 275 MPa and the fracture strain 17.5%. Also, the dynamic compressive strength of the Nicp ESMs sample is higher than that of the Alcp ESMs sample. The reaction characteristics of the two ESMs in different atmospheres were discussed by differential scanning calorimetry. The result showed that the reaction temperature of the Nicp ESMs was lower. Impact-induced energy release tests on the two ESMs were performed to understand their energy release properties. The results showed that the microstructure had significant effects on the ignition velocity threshold and reaction efficiency. The Nicp ESMs has better reaction performance because of the high interface density.

Transparent Polymer Blends of Poly(methyl methacrylate) and Poly(propylene glycol).

Polymer blends, obtained by polymerization of methyl methacrylate in the presence of poly(propylene glycol), are investigated. Poly(propylene glycol) acts as a plasticizer, significantly lowering poly(methyl methacrylate)’s glass transition temperature and decreasing its elasticity modulus and yield stress. The mixture of methyl methacrylate with poly(propylene glycol) is more stable than its mixture with currently used poly(ethylene glycol), which leads to more uniform distribution and higher possible content of the plasticizer. Unlike low molecular weight plasticizers, poly(propylene glycol) is less prone to migration and exudation during manufacturing process and in use, and has low toxicity. Dynamic mechanical thermal analysis, compression testing and X-ray diffraction were used to investigate how the properties of the material depend on the content and molecular weight of the poly(propylene glycol) in the polymer blend. It was shown that the dependence of the glass transition temperature of methyl methacrylate polymerized in the presence of poly(propylene glycol) on the molar fraction of propylene glycol units is linear, and poly(propylene glycol) with lower molecular weight affects properties of the material stronger than poly(propylene glycol) with higher molecular weight. Therefore, the addition of poly(propylene glycol) allows to control the properties of poly(methyl methacrylate) easily and within wide range.

The relation among the stored energy, microstructure and hardening effect of SA508-III steel under different deformation conditions

The stored energy during deformation under different strains, strain rates and deformation temperatures was investigated in this paper. Thermal simulation compression and dynamic compression tests were carried out to obtain the deformed specimens with different strains, strain rates and deformation temperatures. By means of electron backscatter diffraction (EBSD) analysis, the stored energy per volume under different deformation conditions was measured. Then, the effects of strain, deformation temperature, and strain rate on the stored energy were analyzed. The increase of strain and strain rate and the decrease of temperature are conducive to the accumulation of stored energy. The correlations between the stored energy and microstructure parameters including grain and subgrain size were determined. The results show that the grain size is inversely proportional to the stored energy, while the subgrain size is inversely proportional to the square root of the stored energy. The hardening effect during plastic deformation was well described from the side of stored energy. The stress-strain relationship and hardening rate can be accurately predicted based on the evolution of stored energy. A convenient method for the acquisition of stored energy through hardness measurement was provided based on the relationship between hardness and stored energy. The proportion of the stored energy to the plastic work and its dependence on the deformation conditions were discussed. It is concluded that the stored energy can be a comprehensive quantity to connect and analyze the macro and micro behavior in the plastic deformation.

Effects of Strain Rate and Temperature on Physical Mechanical Properties and Energy Dissipation Features of Granite

Dynamic compression tests of granite after thermal shock were performed using the split Hopkinson pressure bar system, to determine the effects of strain rate and temperature on the dynamic mechanical parameters, energy dissipation features and failure modes of granite. The results indicate that the dynamic compressive strength increased exponentially with strain rate and decreased with increasing temperature. Temperature and incident energy can equivalently transform for the same dynamic compressive strength. Dynamic elastic modulus of granite decreased obviously with increasing temperature but did not have a clear correlation with strain rate. As the impact gas pressure increased, the stress-strain curves changed from Class II to Class I behavior, and the failure modes of specimens transformed from slightly split to completely pulverized. The critical temperature at which the stress-strain curves changed from Class II to Class I was determined to be 300 °C, when the impact gas pressure is 0.6 MPa. As the applied temperature increased, density, wave velocity and wave impedance all decreased, meanwhile, the degree of granite specimen crushing was aggravated. Under the same incident energy, as the temperature increased, the reflected energy increased notably and the absorbed energy increased slightly, but the transmitted energy decreased. For the same temperature, the reflected and absorbed energies increased linearly as the incident energy increased, whereas the transmitted energy increased logarithmically. The SEM images of the thermal crack distribution on the granite specimen surface at different temperatures can well explain the essence of mechanical parameters deterioration of granite after thermal shock. This work can provide guidance for impact crushing design of high temperature rocks during excavations.

Microstructure evolution and mechanical properties of as-annealed and solution treated Al-Cu-Li alloy 2195 under dynamic compression

The application prospect of 2195 alloy in aerospace structure parts has received widespread attention. The high strain rate forming combined with heat treatment process is a potential way to produce the high performance Al-Cu-Li alloy parts. In this work, the mechanical properties and microstructure evolution of the as-annealed and solution treated 2195 alloy specimens under dynamic compression were studied and compared. The dynamic compression tests were performed at the strain rates of 1400 s −1 , 2200 s −1 , 3400 s −1 , and 4500 s −1 by split Hopkinson pressure bar . The results indicate that the mechanical properties of the two kinds of heat-treated specimens have been improved by dynamic compression, an increase of 59.7 % and 63.1 % of hardness respectively. The main strengthening mechanisms of the specimen under dynamic compression conditions are fine grain strengthening, dislocation strengthening, and low angle grain boundaries strengthening , which differs depending on the heat-treated state and the strain rate . Besides, it is found that the stable-end orientation of grain rotation in the two kinds of heat-treated specimens after dynamic compression is <110 > //CD (CD: compression direction). Different from the as-annealed specimen, the solution treated specimen shows insufficient grain rotation behavior. The mechanism of insufficient grain rotation is revealed by the Schmid factor . The Schmid factor of as-annealed specimen increases by 7.5 % than that of solution treated specimen. The lower Schmid factor makes the plastic deformation resistance of solution treated specimen higher, which contributes to the insufficient grain roration behavior.

Experimental investigations of static mechanical properties and failure characteristics of damaged diorite after dynamic triaxial compression

To investigate the static mechanical properties and failure characteristics of damaged rocks after impact under realistic in-situ stress, dynamic triaxial compression tests with different strain rates and confining pressures were conducted on diorite by a modified split Hopkinson pressure bar . The damage factor was calculated according to the change of the longitudinal wave velocity of rocks before and after the impact, and the residual strengths of the damaged diorite were obtained by uniaxial compression and Brazilian tensile tests . In addition, three brittleness indexes based on the residual strength were adopted to evaluate the brittleness of damaged specimens, and fractal dimension was introduced to study the fragmentation characteristics. The results show that the dynamic peak stress, strain, elastic modulus , damage factor and plastic deformation of diorite all increase with increasing strain rate, i.e., rate dependence, and the increasing rate decreases with increasing confining pressure. The increment in confining pressure leads to the increase of dynamic peak stress, elastic modulus, static residual strength and brittleness, and the increasing rate increases with increasing strain rate, while other physio-mechanical parameters decrease with confining pressure. The post-peak behavior of dynamic stress-strain curves is divided into two classes according to the strain rate and fracture state of rocks under dynamic loading. Upon the strain rate increases above 87 s −1 , the brittleness of damaged specimens generally decreases to moderately brittle or even low brittle, and the corresponding drillability becomes much easier. The fractal dimension of damaged specimens increases with the increase of confining pressure and decreases linearly with the increase of strain rate .

Dynamic uniaxial compression testing of veined rocks under high strain rates

The occurrence of strainbursts is of major concern in underground deep mining operations. Strainbursts are complex events characterized by a spontaneous strain-energy liberation at the boundaries of underground excavations, putting both the long-term safety of operations and exposing workers to risk. In this study, we reported a series of uniaxial compression tests by using a split Hopkinson pressure bar (SHPB) and a high-speed camera, to understand the role of dynamic loads and high strain rates (10–102 s-1) in the mechanical behavior and fracture patterns of veined rocks. The samples are representative of major deep underground mine districts in Chile: Chuquicamata (QS), Andina (RB), and El Teniente (CMET). Results show a clear increase in the dynamical uniaxial strength concerning quasi-static values. The increase was up to 2,2 times in CMET, 1,8 in RB, and 2,6 in QS. Additionally, the dynamic increase factor (DIF) indicates a strong strain rate dependency of the QS samples. This effect on RB and CMET samples is less evident. The data obtained with dynamic compressional testing indicates that both the increase in stiffness and dynamical compressive strength depends largely on the rock strain rate dependency. Further, we report a direct relationship between fracture patterns and the presence of veinlets. We suggest that fractures propagate through the matrix when the mechanical properties show a strong strain rate dependency, whereas are restricted to veinlets and veins when this dependence is less evident. Thus, as stress pulses enhance the stiffness, the energy dissipation increases, and the proneness of block formation is higher. These are conditions favoring strainbursts occurrence and might increase the severity of this phenomenon in underground excavations.

Research on the Conversion Relationship between Dynamic Point Load Strength and Dynamic Compressive Strength Based on Energy System

Point load test is a simple and fast method to obtain the compressive strength of rock. According to the maximum load at failure and the distance between two cone ends, the compressive strength of specimens can be calculated by the empirical formula. Because the test process does not need to process the sample into laboratory size type, so it is widely used. At the same time, with the rapid development of rock dynamics, the dynamic strength index of rock becomes more and more important under dynamic load. But dynamic point load is seldom mentioned by scholars. In order to explore the correlation between dynamic point load test and dynamic compressive strength, a large number of dynamic point load and uniaxial dynamic compressive strength tests were carried out using a split Hopkinson pressure bar for granite. Based on the energy theory, the crushing energy consumption during dynamic point load and uniaxial dynamic compressive strength tests were statistically analyzed, and the transformational relation between uniaxial dynamic compressive strength and crushing energy consumption during the dynamic point load test was determined. At the same time, the influence of the cone angle on crushing energy consumption during the dynamic point load test was investigated by changing the conical angle. The results show that with the increase in conical angle, the energy consumption of rock crushing decreases gradually during the dynamic point load test. And the decreasing trend tends to be gentle. The conclusion can provide a reference for obtaining the numerical value of the dynamic compressive strength of the rock in the future.

In-Depth Analysis of the High Strain Rate Compressive Behavior of RTM6 Epoxy Using Digital Image Correlation.

The aim of this paper is to study the effect of strain rate on the compressive behavior of the highly cross-linked RTM6 epoxy resin used in advanced aerospace composites. Dynamic compression tests were performed using a split Hopkinson pressure bar, along with reference quasi-static compression tests, to cover a strain rate range from 0.001 to 1035 s−1. Special attention was paid to the optimization of the test methodologies in order to obtain material data free of bias related to the use of different load introduction techniques and sample geometries over the considered strain rate range. In addition, the use of full-field 3D deformation measurements allowed the validation of traditional test and material assumptions. A novel self-alignment tool was developed to enable perfect interfacial contact during compression loading. The 3D digital image correlation technique was used to measure the instantaneous deformation of the sample during compression at different strain rates. Results showed a pronounced strain rate sensitivity of the RTM6 epoxy in compression. The peak yield strength increased with increasing strain rate, while the elastic modulus and Poisson’s ratio in compression were independent of the strain rate. The barreling of the sample in compression, quantified by the barreling ratio, showed an increase during the progression of the compression tests. However, the barreling ratio significantly decreased with the increasing strain rate. Finally, it was shown that neglecting the significant volume change in the yield stages gave rise to a non-negligible underestimation of the strength of the material.

Application and validation of fly ash based geopolymer mortar as grouting material in porous asphalt concrete

To verify the feasibility of using fly ash based geopolymer (FAG) mortar in the porous asphalt concrete, the FAG was designed as the grouting material to fabricate the semi-flexible asphalt mixture. The fluidity of the fresh FAG mortar and the mechanical properties of cured FAG were firstly investigated to characterize its workability. The fulfilling status of FAG grouting asphalt concrete (FAGAC) was validated by both the theoretical calculation method and 3D-CT scanning method. In addition, the interfacial energy parameters between the FAG and the asphalt matrix was investigated. Then, the road performance was extensively studied using the dynamic uniaxial compression test, semi-circular bending test, moisture resistance test and fatigue test. The results showed that the water–solid (W/S) ratio of FAG mortar significantly affected the technical performance of FAG mortar and FAGAC. The mechanical strength of cured FAG mortar, high-temperature stability and moisture resistance of FAGAC decreased with the increase of W/S ratio. Meanwhile, the low-temperature crack resistance, anti-fatigue performance and the interface energy between FAG and asphalt matrix firstly increased with the increase of W/S value, then decreased as the W/S ratio exceeded 0.45. The optimum parameters for FAGAC were reckoned as 24% residual air voids of asphalt matrix, 0.45 W/S ratio of FAG which filling 90% volume of matrix voids. Finally, the ranking priority for the factors affecting the FAGAC performance was specified, including the compression strength of cured FAG mortar, the interface energy between FAG and asphalt matrix, as well as the residual air voids of FAGAC.

Multi-scale collaborative optimization of lattice structures using laser additive manufacturing

In the present work, an effective and efficient design approach is proposed to obtain a three-dimensional multi-scale graded lattice structure by virtue of multiple control parameters via density-based topology optimization. To balance the computational accuracy and cost, a Parameterized Interpolation of Lattice Structure (PILS) model was established, and the math formula combined two novel designing parameters: relative density at macro-scale and aspect ratio at micro-scale. A multinomial function was employed to describe the explicit association between control parameters and equivalent elastic constants with regard to relative density and aspect ratio, which avoided tedious homogenization computation burden in the structural optimization process. Consequently, the multi-scale collaborative design approach could optimize the macro material density distribution and the micro cell topology in an integrated manner. Numerical examples with respect to compliance optimization were offered to validate the benefits of the proposed approach. Finally, the quasi-static and dynamic compression tests were respectively implemented by universal testing machine and Split Hopkinson Pressure Bar (SHPB) system on lattice structures manufactured by laser powder bed fusion (LPBF). The outcomes reveal that graded lattice structures exhibit remarkably improved load-bearing performance than the uniform lattice structures.

Influence of twins found in adiabatic shear bands on dynamic recrystallization of a near β Ti-5.5Mo-7.2Al-4.5Zr-2.6Sn-2.1Cr alloy

Much efforts have been made on the studies of the microstructure evolution near adiabatic shear bands (ASBs) in titanium alloys. However, the deeper evolution mechanism is not very clear. Therefore, in the present, the dynamic compression test utilizing split Hopkinson pressure bar at room temperature and a strain rate of ∼3000/s was carried out on a hot-rolled near β-typed Ti-5.5Mo-7.2Al-4.5Zr-2.6Sn-2.1Cr alloy, and the microstructures of the central region and the transition region of the adiabatic shear bands were carefully investigated by high-angle annular dark field-scanning transmission electron microscope (HAADF-STEM). It was found that the central region of ASBs was composed of the softening regions (SRs) and the hardening regions (HRs). Moreover, detailed observation indicated that in the SRs, the microstructure consisted of dynamic recrystallization (DRX) grains. While in the HRs, the {11–22}<11-2-3> twin in α grains and the {332}<113> twin in β grains were observed, and a great number of dislocations were accumulated at the interface of twins and parent phases (α and β phases) to form dislocation walls, thus promoting the DRX process in the ASB central region. It illustrated a new DRX mechanism in ASBs. Meanwhile, no twins were found in the ASB transition region. Further research on the average compositions of α and β phases in the HRs of ASBs by energy dispersion spectrum method combined with d-electron theory revealed that the twin in α grains was mainly caused by the severe deformation under dynamic loading, while that in β phase was the result of the instability of β phase.

Experiment and mesoscopic modelling on the dynamic compressive behaviors of a new carbon fiber-reinforced cement-based composite

This paper presents an experimental and numerical study on the compressive behaviors of a new carbon fiber-reinforced cement-based composite (CFRCC) that is composed of magnesium oxysulfate cement, carbon fiber and some chemical admixtures. Parametric studies on the effects of carbon fiber content and strain rate on the compressive behaviors of CFRCC, are conducted using a series of quasi-static and dynamic compressive tests. The research item includes the failure morphology, stress-strain curve, dynamic increase factor (DIF), etc. Besides, a three-dimensional (3D) mesoscale modelling approach is proposed to simulate and analyze the mechanical responses and the failure mechanisms of CFRCC subjected to dynamic compressive loading, where the random dispersion of chopped fibers are realistically considered. The results indicate that the cracking and failure modes of CFRCC are significantly affected by the bridging effect of carbon fibers randomly dispersed in cement matrix. With the increase of fiber content, the dynamic peak stress and peak strain of CFRCC at similar strain rates show an increasing and decreasing trend, respectively. An evident strain-rate hardening effect could be found on the initial elastic modulus and the peak stress of CFRCC as well. While the relationship between the DIF of CFRCC and the logarithm of strain rate could be described using a quadratic function. Moreover, the mesoscale modelling approach has been validated by a good agreement between the numerical and tested results, demonstrating the feasibility of the developed mesoscale model in simulating and investigating the dynamic behaviors of CFRCC. All in all, the CFRCC has proven to be of great significance in resisting to impact loads, and more insights should be provided into its dynamic properties.

Experimental investigation of automotive component in hybrid fibre reinforced thermoplastic design

A tailored use of continuous fibre reinforced plastics enables application in high volume car body structures. The combination of pultruded, load carrying, unidirectional, continuous fibre reinforced thermoplastic (FRTP) profiles and injection moulds, named “skeleton design”, is a promising approach to meet structural requirements and economical needs. This design offers the advantages of FRTP such as short cycle times of approx. 75 s and functional integration via injection moulding. A pre-serial BMW iX geometry of a windshield panel is used to analyse the impact of different fibre configurations in the profiles on the mechanical properties of the part. Therefore, different pultruded profiles with a cross-section of 10 mm x 10 mm made of polyamide 6 (PA6) with carbon fibres (CF) and glass fibres (GF) as well as a CF/GF hybrid were used. Furthermore, an optimized part using different materials within one part was investigated. Therefore, quasi-static and dynamic compression tests were performed on part level. It could be shown that the optimized parts meet mechanical requirements while decreasing material costs significantly.

Effects of particle shape on dynamic mechanical behaviours of coral sand under one-dimensional compression

Coral sand is characterized by high porosity, high compressibility and high crushability mainly due to its irregular particle shape and internal pore structure. Single coral particles in a size fraction tend to have a variety of shapes from bulky to flaky, which emerges as one of the most pivotal factors affecting the macro-scale performances of coral sand. A series of confined one-dimensional dynamic compression tests were conducted on coral sand with four classified shapes (e.g., blocky, dendritic and rodlike, flaky particles, and coral debris) via a modified 37-mm-diameter split Hopkinson pressure bar (SHPB) apparatus. The effects of particle shape on the dynamic mechanical behaviours of coral sand at high strain rates were assessed in terms of the stress-strain response, compressibility, particle breakage and the change in particle shape measures. It is revealed that coral sand exhibits high small-strain stiffness, a low crushing strength, a notable strain hardening and a high compressibility behaviour as subjected to dynamic compression at high strain rates. In the low-stress level, it is the high interparticle friction and interlocking induced by the irregular shape form and rough surface texture that lead to a gentle descending tendency in the void ratio. While in the high-stress level, it is the particle crushing along with its rearrangement that results in the high compressibility of the coral sand assemblage. In general, the particle crushing strength tends to decrease as the particle shape shifts from bulky to elongated and to flaky. The large-strain stiffness decreases and the compressibility increases with an increase in the overall particle irregularity. Coral particles are prone to be more spherical and smoother as the average degrees of sphericity, convexity and aspect ratio approach to unity, due mainly to the intense asperity damage and primary fracture under dynamic tests. Furthermore, the percentage in the degrees of sphericity, convexity, aspect ratio and flatness increases with respect to the initial degrees of themselves. It can be further postulated that the extent of breakage could be quantified by the statistical change in the particle measures such as sphericity and convexity aside from particle dimensions for granular materials with irregular shapes.