Dynamic Compressive Mechanical Properties Research Articles

Experimental Study on Dynamic Compression Mechanical Properties of Aluminum Honeycomb Structures

In this paper, dynamic compression tests are developed to investigate the dynamic compression mechanical properties of the aluminum honeycomb structures at different strain rates, especially at the high strain rates. The difficulties at the high strain rates exist due to the large deformation, the low wave resistance and the size effect of the honeycomb structures. The Split Hopkinson Pressure Bar (SPHB) test method is carried out and special measures such as the adoption of waveform shaper, the size optimization of the impact bar and the specimen, and employment of the semiconductor strain gauge, etc. are taken to overcome the difficulties. It is discovered that the dynamic compression mechanical properties possess a stress hardening effect at a high strain rate from 1.3 × 103 s−1 to 2.0 × 103 s−1, but then a stress softening effect at a high strain rate of 4.6 × 103 s−1. It is also discovered that the yield strength and the average plateau stress at the strain rate of 2.0 × 103 s−1 is higher than that at the strain rate of 1.3 × 103 s−1. However, the yield strength and the average plateau stress at the strain rate of 4.6 × 103 s−1 is lower than that at the strain rate of 2.0 × 103 s−1 and 1.3 × 103 s−1, but higher than that at a quasi-static state. This indicates that the aluminum honeycomb structure is sensitive to the strain rate. Additionally, the damage mode of the aluminum honeycomb structure is plastic buckling, collapse and folding of the cell wall, which is carried out using dynamic compression tests. The folding length of the cell wall at a higher strain rate is found to be longer than that at a lower strain rate. The test results can also be used as the stress–strain curves of the honeycomb constitutive model at the high strain rates to carry out the numerical simulation of high-speed impact.

Experimental Investigation of Dynamic Compression Mechanical Properties of Frozen Fine Sandstone

Aiming at the dynamic mechanical properties of weakly cemented fine sandstone in the rich water‐bearing strata in western China under dynamic loading, a 50 mm rod diameter separation Hopkinson pressure bar (SHPB) test was used to study the Paleogene fine sandstone in a coal mine in Ningxia. The system carried out the impact compression tests of −15°C, −20°C, and −30°C and the average strain rate of 28 s−1–83 s−1 and obtained the dynamic compressive strength of the frozen fine sandstone specimens under different test conditions. The strain curve and the fracture morphology were analyzed for the relationship between dynamic peak stress, peak strain, dynamic strength growth coefficient (DIF), and fracture morphology and strain rate. The results show that the peak stress of frozen fine sandstone increases from the decrease of freezing temperature under the same average strain rate. The peak stress of the specimen increases from the increase in the average strain rate of the same freezing temperature. The failure modes of specimen are mainly divided into axial splitting tensile failure and compression crushing failure. To the splitting tensile failure and the compression crushing failure, the main factors determining the two failure modes are the strain rate, while the temperature affects the severity of the impact damage. In the load strain rate and temperature range, the DIF of the frozen fine sandstone is linearly correlated with the strain rate, and the lower the temperature, the slower the growth rate of the DIF.

Experimental Study on Static and Dynamic Compression Mechanical Properties of Filled Rock Joints

The static and dynamic compression mechanical properties of the prefabricated artificial filled rock joints specimens with different fillings and different joint thicknesses are tested, respectively. Then, the strength, deformation, wave propagation and energy dissipation laws of the filled joints are analyzed. The experimental results show that the static and dynamic compression strength of filled joints increases with the strength of filling materials while decreases with the filling thickness. The deformation characteristics of filled joints under static and dynamic compression are positively correlated with the properties of filling materials and the thickness of filled joints. With the increasing of the filling thickness, the reflection coefficient increases while the transmission coefficient decreases. With the increase of the strength of the fillings, the reflection coefficient decreases while the transmission coefficient increases. The energy dissipation ratio decreases with the increase of the filliing thickness and increases with the increase of the strength of the filling material.

Compressive behavior and constitutive model of polyurea at high strain rates and high temperatures

To study the dynamic compressive mechanical properties of polyurea at strain rate range of 1400 s−1–5700 s−1 and high temperature range of 20 ℃–80 ℃, we conducted a dynamical mechanical experiment utilizing a split Hopkinson pressure bar (SHPB) system. The compressive stress-strain curves of polyurea under various strain rates and temperatures are analyzed and discussed. The experimental results indicated that the strain rate and high temperature can remarkably influence the mechanical behaviors of polyurea, compression behaviors increased with the increasing of strain rate and compression behaviors decreased with the increasing of temperature. In addition, a thermal-visco-hyperelastic constitutive model based on five-parameter Mooney-Rivlin model was proposed to describe the compression stress-strain behavior of polyurea over a wide range of strain rates and temperatures. The model parameters were obtained by fitting the experimental stress-strain curves. The model prediction results show good agreement with the experimental results.

The influence of graphene on the dynamic mechanical behaviour of shear thickening fluids

The viscosity and shear thickening efficiency of the nanoparticle-based shear thickening fluids (STFs) were influenced by hydrodynamic lubrication force between nanoparticles. To enhance such an influence and improve the performance of STF, graphene was adopted to reinforce SiO2 nanoparticle-based STF in this paper. The viscosity of the reinforced STF was improved obviously by graphene, which makes an increase of 30% compared to the pure STF. In order to characterize the influence of graphene on the flow stress of STF at high strain rates, a split Hopkinson pressure bar was implemented to test the dynamic compressive mechanical properties at strain rates in the range from 3 × 103 to 104/s. The results showed that graphene has a significant influence on the flow stress of reinforced STF at different strain rates compared to the pure STF, and the effects of the strain rate and graphene volume fraction on the flow stress were analyzed. Based on the hydrodynamic lubrication force theory, the attribution done by grahpene to the hydrodynamic lubrication force in STF was discussed. The results of the paper provide an efficient way to develop a novel STF with high shear thickening efficiency.

Study on microcrack growth-based dynamic compressive mechanical properties in brittle rocks

The dynamic microcrack growth has a great influence on the macroscopic dynamic mechanical properties of brittle rocks under dynamic compressive loadings. However, the relationships between dynamic microcrack growth and macroscopic dynamic mechanical properties are rarely studied. Based on the microcrack growth-induced stress-strain constitutive relationship, the relationship between quasi-static and dynamic fracture toughness, the relationship between crack velocity and strain rate, the relationship between strain rate and dynamic fracture toughness, a micromechanics-based stress-strain constitutive model is proposed. Furthermore, the relationship between crack velocity and strain rate is derived by the time derivative of equation describing the relationship between crack length and axial strain. The relationship between strain rate and dynamic fracture toughness is obtained by coupling the suggested relationship between crack velocity and strain rate, and the crack velocity and fracture toughness. Effects of strain rate on stress-strain relation and dynamic compressive strength are studied. The reasonability of the proposed dynamic constitutive model is verified by the experimental results. Sensitivities of initial damage, confining pressure, parameters m, e0 and R on stress-strain relation, dynamic compressive strength and dynamic elastic modulus are discussed. These studies will provide a certain theoretical help for analyzing the stability of brittle surrounding rocks in deep undergrounding engineering.

Characterization of dynamic and quasistatic compressive mechanical properties of ice-templated alumina–epoxy composites

Abstract

Dynamic Compressive and Tensile Characteristics of a New Type of Ultra‐High‐Molecular Weight Polyethylene (UHMWPE) and Polyvinyl Alcohol (PVA) Fibers Reinforced Concrete

The dynamic mechanical properties of concrete materials are important parameters for evaluating the safety performance of concrete structures under dynamic loads. Fiber cement‐based materials have been widely used in the construction projects due to their strength, toughening, and cracking resistance. In this study, we conducted experimental and theoretical studies on dynamic compression and tensile mechanical properties of different proportions of new‐type fiber concrete. A Split‐Hopkinson pressure bar equipment was used to determine the concrete behavior at different strain rates. The effects of strain rate and fiber content on the strength of the specimen, dynamic increase factor, and ultimate strain were analyzed. Based on the macrodamage factor, the traditional nonlinear viscoelastic constitutive model was simplified and improved. The four‐parameter constitutive model was obtained, and the influence of these parameters on the performance of fiber concrete was analyzed. The experimental results were compared with those predicted from the available equations, and results were in accordance. Finally, an analytical equation for predicting the dynamic compression and tensile properties of these new‐type fibers was proposed.

Dynamic strength enhancement and strain rate sensitivity in ice-templated ceramics processed with and without anisometric particles

We investigated the effects of platelets and strain rate on the compressive response of ice-templated porous alumina, processed from ultrafine, equiaxed particles and from a mixture of ultrafine, equiaxed and large platelet particles. Results revealed a remarkable enhancement of the quasistatic and dynamic compressive mechanical properties of the templated ceramics in the presence of platelets. Specific compressive mechanical properties of the ice-templated alumina containing platelets are superior in comparison to those of the various metallic, syntactic and natural cellular solids. In the presence of platelets, compressive strength exhibited contrasting strain rate sensitivity between the elastic and inelastic stages of deformation.

Compressive properties of pristine and SiC-Te-added MgB2 powders, green compacts and spark-plasma-sintered bulks

Pristine and (SiC+Te)-added MgB2 powders, green and spark plasma sintered (SPS) compacts were investigated from the viewpoint of quasi-static and dynamic (Split-Hopkinson Pressure Bar, SHPB) compressive mechanical properties The amount of the additive (SiC+Te) was selected to be the optimum one for maximization of the superconducting functional parameters. Pristine and added MgB2 show very similar compressive parameters (tan δ, fracture strength, Vickers hardness, others) and fragment size in the SHPB test. However, for the bulk SPSed samples the ratio of intergranular to transgranular fracturing changes, the first one being stronger in the added sample. This is reflected in the quasi-static KIC that is higher for the added sample. Despite this result, sintered samples are brittle and have roughly similar fragmentation behavior as for brittle engineering ceramics. In the fragmentation process, the composite nature of our samples should be considered with a special focus on MgB2 blocks (colonies) that show the major contribution to fracturing. The Glenn-Chudnovsky model of fracturing under dynamic load provides the closest values to our experimental fragment size data.

Experimental investigations of dynamic compressive properties of roller compacted concrete (RCC)

Roller compacted concrete (RCC) has been widely used in large scale constructions such as hydraulic structures and pavement. Because of the construction process, it has some unique material properties as compared to the ready-mix concrete. Structures made of RCC might be subjected to dynamic loads during its service life. Understanding the dynamic material properties of RCC is essential for better analysis and design of RCC structures. The study on dynamic compressive mechanical properties of RCC is very limited in literature. In this study, dynamic compressive properties of RCC under the strain rate up to 80/s are investigated by using Split Hopkinson Pressure Bar (SHPB). In addition, to investigate the size effects on dynamic impact tests, three sizes of cylindrical RCC specimens with the diameters of 50 mm, 75 mm and 100 mm are prepared and tested. The failure processes and the failure modes of RCC specimens with different dimensions under different strain rates, as well as the stress–strain curves under different strain rates and the energy absorption capacities of the tested specimens are compared. The influences of the specimen size, aggregates grading, and the existence of bedding surface in RCC on its dynamic properties are investigated. Based on the testing results, empirical formulae of DIF (dynamic increase factor) for the RCC compressive strength are proposed to predict the enhancement of material strength at different strain rates.

Experimental evaluation of quasi-static and dynamic compressive properties of ambient-cured high-strength plain and fiber reinforced geopolymer composites

Heat cured geopolymer binders have been studied extensively to establish their mechanical behaviour under quasi-static loading conditions and it has been found that they are capable of achieving comparable and in some cases better properties than ordinary Portland cement (OPC). However, as a novel binding material, minimal research has been conducted to understand their dynamic material response. This paper presents the dynamic compressive properties of a newly synthesized high-strength ambient cured geopolymer mortar and hybrid steel-polyethylene fiber reinforced geopolymer composite (FRGC). Dynamic compressive tests are carried out using the Ø100-mm split Hopkinson pressure bar (SHPB) apparatus with pulse shaping technique whereas a 160-ton hydraulic test machine is used for quasi-static compressive tests. The dynamic compressive properties of plain and FRGC including stress–strain curves, strength enhancement, impact toughness and energy absorption capability are obtained and compared with those observed under quasi-static actions. A high-speed camera is used to record the failure processes of samples under impact. The test results show that the dynamic compressive mechanical properties of plain and FRGC exhibit strong strain rate dependency. The DIFs (dynamic increase factors) of samples increase approximately linearly with the average strain rate in a logarithmic manner. Obvious binomial relationships are noticed between the energy absorption capacity and average strain rate of tested samples, such that the strain rate sensitivity threshold exists at 30 s−1 and 66 s−1 for plain and FRGC materials, respectively. Empirical DIF relations are proposed which can be used to model the developed composite materials and structures subjected to static and impact loads.

Effects of steel fiber content and type on dynamic compressive mechanical properties of UHPCC

The split Hopkinson pressure bar (SHPB) test on Ultra-high performance cementitious composites (UHPCC) specimens is performed, in which the strain rate ranges from 17.6 s−1 to 328.4 s−1 and two typical steel fibers (micro-straight and hooked) with three volume fractions of 0%, 1.0% and 2.0% are considered. It indicates that, (i) the dynamic elastic modulus, compressive strength and peak strain as well as the toughness of UHPCC increase obviously with the increase of strain rate; (ii) the steel fiber content and type almost have no effects on the dynamic elastic modulus and peak strain, and show relatively small strengthening effects on the dynamic compressive strength of UHPCC; (iii) the present micro-straight steel fiber has slightly better effect on improving the dynamic compressive strength than the hooked steel fiber, particularly for the steel fiber volumetric ratio of 2.0%; (iv) the peak dynamic toughness almost has no relation to the steel fiber reinforcement, while the ultimate dynamic toughness increases with increasing the steel fiber content, and the influence of the micro-straight steel fiber is more obvious. Furthermore, the empirical dynamic increase factors (DIFs) for the dynamic compressive strength of UHPCC are formulated, and a modified visco-elastic damage model is established for UHPCC under dynamic loadings.

Experimental and modeling investigation on the dynamic response of granite after high-temperature treatment under different pressures

In this work, the dynamic compressive mechanical properties of Beishan granite are investigated under the condition of uniaxial load and confined pressure, respectively. The purpose of this investigation is to study the effect of hydrostatic pressure and pre-heating temperature on the strength property and failure of such material. The investigation is carried out with the use of a large-diameter split-Hopkinson pressure bar (SHPB), which is equipped with an active confining device. The dynamic stress–strain behaviors of the granite samples under different confined conditions are obtained with a pre-heating temperature ranging from 25 to 800°C. We analyzed the temperature-dependent variation of the peak stress, peak strain and elastic modulus of the material under selected values of confined pressure. It is observed that the uniaxial compressive behavior of Beishan granite under unconfined pressure is strongly dependent on the pre-heating temperature. The values of the peak stress and the elastic modulus both decrease as the pre-heating temperature increases, while the value of the peak strain increases with the rise of pre-heating temperature, indicating a characteristic change from elastic-brittle to elastic–plastic. Under confined pressure, the strength of the material can be greatly improved, and higher pre-heating temperature tends to bring down the value of the strength. With the confined configuration, the strengthening of the peak stress is not significantly associated with the value of the confined pressure; instead the dependence on the strain rate becomes more remarkable. For the temperature effect, the value of the peak stress can be linearly correlated with the temperature level through comparative analysis. Moreover, the elastic modulus of the material can be associated with the temperature by a functional form, known as the temperature shift factor. Finally, an elastoplastic-damage constitutive model is established to predict the dynamic mechanical behavior of the material after high-temperature treatment under different confined pressures.

The dynamic compressive response of a high-strength magnesium alloy and its nanocomposite

The dynamic compressive mechanical properties of the alloy Mg-4Zn-3Gd-1Ca (wt%) and its nanocomposite Mg4Zn3Gd1Ca-2ZnO were investigated at strain rates up to 1×103s−1, using a Split Hopkinson Pressure Bar (SHPB) tester. Under dynamic loading, the addition of 2wt% ZnO nanoparticles into the alloy generated a significant strength increase (~100MPa), attributed largely to grain refinement. Negative strain rate sensitivity of the alloy and its nanocomposite was observed. It is postulated that the strengthening influence of the nanoparticles by retarding twin nucleation/growth at grain boundaries, is significantly weakened as strain rate increases. The yield stress of the materials studied follows the Hall-Petch relationship even when the grain size is less than 1µm. It is proposed that the strong solute strengthening from Gd and Ca enhances the critical resolved shear stress for slip and preserves tension twinning as the dominant deformation mechanism for yielding.

Dynamic mechanical behavior of ultra-high strength steel 30CrMnSiNi2 A at high strain rates and elevated temperatures

During high speed machining in the field of manufacture, chip formation is a severe plastic deformation process including large strain, high strain rate and high temperature. And the strain rate in high speed cutting process can be achieved to 105 s−1. 30CrMnSiNi2 A steel is a kind of important high-strength low-alloy structural steel with wide application range. Obtaining the dynamic mechanical properties of 30CrMnSiNi2 A under the conditions of high strain rate and high temperature is necessary to construct the constitutive relation model for high speed machining. The dynamic compressive mechanical properties of 30CrMnSiNi2 A steel were studied using split Hopkinson pressure bar (SHPB) tests at 30 – 700 °C and 3000 – 10000 s−1. The stress-strain curves of 30CrMnSiNi2 A steel at different temperatures and strain rates were investigated, and the strain hardening effect and temperature effect were discussed. Experimental results show that 30CrMnSiNi2 A has obvious temperature sensitivity at 300 °C. Moreover, the flow stress decreased significantly with the increase of temperature. The strain hardening effect of the material at high strain rate is not significant with the increase of strain. The strain rate hardening effect is obvious with increasing the temperature. According to the experimental results, the established Johnson-Cook (J-C) constitutive model of 30CrMnSiNi2 A steel could be used at high strain rate and high temperature.

Mechanical Properties of MWCNTs/PA66 Composites under Impact Loading

PA66 reinforced with different weight content of multi-walled carbon nanotubes (MWCNTs) were prepared using a twin-screw extruder. The quasi-static and dynamic compression mechanical properties were investigated. Addition of 2.5 wt% P-CNTs to PA66 achieves the best enhancement effect.

Study on Dynamic Compressive Mechanical Properties and Failure Modes of Heat-Treated Granite

DYNAMIC COMPRESSIVE PROPERTIES AND FAILURE MODES OF HEAT-TREATED GRANITE ARE EXPLORED BY USING THE IMPROVED SPLIT HOPKINSON PRESSURE BAR (SHPB). THE RESULTS SHOW THAT THE AMPLITUDE OF INCIDENT WAVE INCREASES WITH THE IMPACT VELOCITY OF STRIKER, AND THE SHAPES OF THE TRANSMITTED AND REFLECTED WAVES ARE CLOSELY RELATED TO THE FAILURE STATE OF THE SPECIMEN. THE STRESS-STRAIN CURVES FOR THE HEAT-TREATED SPECIMENS ABOVE 700OC ARE OBVIOUSLY DIFFERENT TO THOSE BELOW 500OC IN TERMS OF THE SLOPES FOR THE ASCENDING SEGMENT AND THE PEAK STRESS, INDICATING THAT THERE IS A TEMPERATURE THRESHOLD BETWEEN 500OC AND 700OC. UNDER THE SAME VELOCITY, THE STRAIN RATE DECREASES SLIGHTLY AND THEN INCREASES AS THE TEMPERATURE INCREASES. AT A CONSTANT TEMPERATURE, STRAIN RATE INCREASES LINEARLY WITH THE IMPACT VELOCITY. THE RELATIONSHIP BETWEEN ELASTIC MODULUS AND STRAIN RATE FOR THE HEAT-TREATED SPECIMEN OBVIOUSLY TENDS TO HAVE NO REGULARITY. IN ADDITION, BOTH PEAK STRESS AND PEAK STRAIN EXHIBIT STRAIN RATE SENSITIVITY, BUT DIFFERENT INCREASING RATES FOR DIFFERENT TEMPERATURES ARE DETECTED. BELOW 500OC, THE INFLUENCE OF TEMPERATURE ON PEAK STRESS AND PEAK STRAIN IS NOT EVIDENT, HOWEVER, THE INFLUENCE BECOMES REMARKABLE AT 700OC AND 900OC.

Biomimetic nucleus pulposus scaffold created from bovine caudal intervertebral disc tissue utilizing an optimal decellularization procedure.

Intervertebral disc (IVD) degeneration (IDD) and herniation (IDH) can result in low back pain and impart significant socioeconomic burden. These pathologies involve detrimental alteration to the nucleus pulposus (NP) either via biochemical degradation or extrusion from the IVD, respectively. Thus, engineering living NP tissue utilizing biomaterial scaffolds that recapitulate native NP microarchitecture, biochemistry, mechanical properties, and which support cell viability represents an approach to aiding patients with IDD and IDH. To date, an ideal biomaterial to support NP regeneration has yet to be developed; however, one promising approach to generating biomimetic materials is to employ the decellularization (decell) of xenogeneic NP tissue to remove host DNA while maintaining critical native extracellular matrix (ECM) components. Herein, 13 different procedures were evaluated in an attempt to decell bovine caudal IVD NP tissue. An optimal method was identified which was confirmed to effectively remove bovine DNA, while maintaining physiologically relevant amounts of glycosaminoglycan (GAG) and type II collagen. Unconfined static and dynamic compressive mechanical properties of scaffolds approached values reported for human NP and viability of human amniotic stem cells (hAMSCs) was maintained on noncrosslinked and EDC/NHS treated scaffolds for up to 14 days in culture. Taken together, NP tissue obtained from bovine caudal IVDs can be successfully decelled in order to generate a biomimetic scaffold for NP tissue regeneration. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 3093-3106, 2016.

Compressive response of multiple-particles-polymer systems at various strain rates

Multiple-particles-polymer systems of a polyurethane elastomeric matrix embedding 25wt.% and 50wt.% 0.5 mm-diameter PMMA particles were investigated using a split Hopkinson pressure bar (SHPB) setup for revealing the dynamic compressive mechanical response. Taking the 25wt.%-particles-polymer system as a reference case, the characteristics of the dynamic stress–strain relation were quantified and analyzed. Yield stress, maximum stress and strain energy show strain rate dependent behaviour, following a power law function. Based on the power law functions, a strength–toughness relation induced by strain rate was derived. The static and dynamic compressive mechanical properties of the 25wt.%-particles-polymer system and these of the monolithic polyurethane elastomeric material were compared. A high-speed camera was applied to record crack initiation, propagation, interaction and final fragmentation. Scanning electron microscopy (SEM) was employed to explore the damage mechanisms of the multiple-particles-polymer system. By comparing the dynamic compressive data of the 25wt.%- and 50wt.%-particles-polymer systems, the multiple particles effect on the dynamic compressive response was analysed. The results of this study are of significance for developing a transparent particles-polymer framework with a required static stiffness for impact-resistant applications and for designing and evaluating hybrid particles-filled polymer composite material systems.