Dynamic Compressive Loading Research Articles

Dynamic compressive properties of 2D-aligned steel fiber reinforced cement-based composites

Dynamic compression may happen in some protective cement-based composite structures. Cement-based composites are compressed at loading direction when subjected to dynamic compression, however expansion occurs in the direction perpendicular to the loading. As a quasi-brittle material, the expansion of the cement-based composites may result in the disintegration and hence the failure of the material. Incorporating steel fibers is a valid solution of reinforce the composites to resist dynamic compression. Usually, steel fibers are randomly dispersed throughout the composites. Actually, steel fibers with the same direction of the dynamic loading are ineffective. Only steel fibers perpendicular to the orientation of the dynamic compression load can they effectively restrict the expansion of the composites and enhance its dynamic compressive properties. So, cylindrical specimens using two-dimensionally aligned steel fiber reinforced cement-based composites (2D-SFRC) were prepared and tested. In specimens all steel fibers are perpendicular to the dynamic compression load, which limits the circumferential expansion and deformation of the specimens when subjected to dynamic compression and significantly enhances its performance resisting dynamic compression. When preparing 2D-SFRC specimens, the magnetic field was used to align steel fibers to achieve the two-dimensionally aligned steel fiber in specimens. Then, 2D-SFRC specimens were tested for their dynamic compressive properties. The results indicate that the dynamic compressive strength and toughness of 2D-SFRC specimens are significantly increased compared with unidirectional and random steel fiber distribution specimens. By analyzing the stress distribution and tensile force of steel fibers, the reinforcing mechanism of two-dimensionally aligned steel fibers was revealed. The two-dimensional alignment of steel fibers increased the number and the tensile force of fibers, which effectively restrained the circumferential expansion of the cylinder specimens.

Investigation on mechanical properties of Ti-6Al-4 V multilayer micro-lattice biomaterials under dynamic compression loading

Novel skull repair Ti-6Al-4 V multilayer micro-lattice biomaterials (MMBs) proposed recently have promising application in clinical practice. Herein, the dynamic compression performances of MMBs are concerned and investigated by Split Hopkinson Pressure Bar (SHPB) system and finite element (FE) methods. Typical shear band, strut yielding and damage deformation modes of MMBs are characterized by FE and SHPB experiment. Through density gradient regulation, deformation mode of MMBs is transformed from shear band to localized collapse pattern. It is interesting that MMBs with different unit cell sizes exhibit different strain rate sensitivities. For strain rate-insensitive MMBs (BCC(3), BCC(5) and BCCZ(3)), the influence of relative density on strength shows a linear increasing trend under both low and high strain rates. For strain rate-sensitive ones (BCC(7), BCCZ(5) and BCCZ(7)), the influence of relative density on strength under low strain rate is stronger than that under high strain rate. The strength range of MMBs matches skull/bone materials well under same loading strain rate. This work not only reveals dynamic mechanical properties of MMBs but also has enlightenment for investigating dynamic properties of porous metamaterials.

Dynamic behavior of polyethylene terephthalate (PET) foam under compressive loads: Experimental and numerical study

The behavior of PET foam under quasi-static and dynamic compressive loads is analyzed. An experimental study is performed to evaluate its mechanical behavior and energy absorption characteristics at different strain rates. Also, a numerical model is developed to reproduce the dynamic compression behavior of the PET foam. Differences between the properties obtained in the quasi-static and dynamic tests show that the strength, stiffness and energy absorption efficiency are dependent on strain rate. The evolution of the Poisson ratio with strain and strain ratio is studied. A decrease in the Poisson ratio is observed as the strain rate increases.

DIRECT SOLUTION OF THE DYNAMICAL ELASTICITY PROBLEM FOR A QUARTER SPACE

The wave field of an elastic quarter space is constructed when one face is rigidly fixed and a dynamic normal compressive load is concentrated at the point on another face. The problem was solved by the direct application of the integral Laplace and Fourier transforms to the motion equations and the boundary conditions. This operation leads to the one-dimensional vector inhomogeneous boundary value problem with respect to unknown displacement’s transformants. The problem was solved using the matrix differential calculus. A fundamental matrix and a decreasing solution to the corresponding homogenous matrix equation were constructed with a basic residue theorem. A singular integral equation was obtained in the process by satisfying unrealized boundary condition. Weakly convergent part of the equation was summed up. The behavior of the unknown function had been analyzed based on its mechanical sense. The form of unknown function was expressed as a series on Laguerre polynomials. The original displacements’ field was found after an application the inverse integral transforms.

Nonlocal strain gradient-based isogeometric analysis of graphene platelets-reinforced functionally graded triply periodic minimal surface nanoplates

Recent developments in additive manufacturing (AM) technologies have empowered the design and fabrication of intricate bioinspired engineering structures at the nano/micro scale. However, mathematical modeling and computation of these structures are still challenging. The main target of this study is to address an efficient computational approach for predicting the mechanical behavior of graphene platelets (GPLs)-reinforced functionally graded triply periodic minimal surface (FG-TPMS) nanoplates. The computational model integrates both nonlocal elasticity and strain gradient effects into the NURBS-based isogeometric analysis of these small-scale structures. We establish advanced nanoplate models by combining three sheet-based TPMS architectures with two new porosity distribution patterns and three distribution patterns of GPLs across the thickness direction. Moreover, the present work makes a pioneering attempt to elucidate how the stiffness-hardening and stiffness-softening mechanisms influence FG-TPMS nanoplates reinforced with GPLs. Compared with two common cellular solids, the superiority of TPMS architectures' mechanical performance is demonstrated. Among all, P and IWP TPMS types along with symmetric porosity and GPLs distributions exhibit outstanding behaviors under static bending, free vibration, and dynamic instability. Furthermore, we conducted a performance analysis for the first time, showcasing the superior capabilities of TPMS architectures under dynamic in-plane compressive loads, especially when compared to isotropic plates of equal weight. The findings of this study greatly enhance our understanding of the intricate mechanical responses of GPLs-reinforced TPMS architectures at the small-scale level, contributing to future interdisciplinary applications.

Development of novel high damping rubber damper under axial compression dynamic load for energy-dissipation application

High Damping Rubber (HDR) has been a reliable and durable material used in bearings as seismic isolation devices for several decades. However, there has been no development of HDR as dampers to mitigate structural response caused by earthquake excitations, specifically by dissipating the induced energy applied to structures under direct axial load. This paper aims to address this gap by developing a novel HDR damper utilizing Hyper Elastic Composite Material (HECM) and conducting experimental investigations to determine its damping ratio, compressibility, and elasticity behaviour under axial dynamic compression load for effective dissipation of dynamic loads. The research methodology involved performing response spectrum analysis (RSA) on a model of actual building structures, following the guidelines of National Annex to MS EN 1998–2017. Subsequently, the dampers were incorporated into the model to achieve a seismic base shear value without seismic actions, as determined by the RSA. Full-scale dampers were then developed using three different HECM variants (NR- A, B and C), selected based on their achievement of a damping ratio of more than 10% as bearing isolators using the shear method according to EN 15129:2009 cl. 8.2.4.1.5. The developed dampers underwent testing for damping and wind load in accordance with EN 15129 cl. 7.4.2.7 and cl. 7.4.2.8, respectively, incorporating the testing parameters derived from the model's RSA. Finite element models (FEM) were developed and accurately simulating the hysteresis curves and damping properties of the HDR damper. The properties of HECM in the FEM were derived from the simulation results and can be utilized for future damper design, ensuring compliance with industry requirements. Additionally, an empirical formula will be developed to enable structural designers to estimate the mechanical properties of the tested damper. The testing shows that NR-C HECM damper is able to achieve 10.46% under 1.8 Hz requirement and able to exceed more than10% damping ratio up to frequency 2.3 Hz, thus providing an alternative energy dissipation damper in the building industry.

Failure and acoustic behavior of combinational flaws sandstone subjected to dynamic compression loads

This paper described work initiated with two objectives in mind. First was to explore the influence of strain rate effects on the strength law and deformation characteristics of plate sandstone with combined flaws. Second objective was to analyze the breaking response law and acoustic behavior of flawed sandstone under the influence of disturbance frequency and prefabricated dip angle. Thus, a self-developed physical simulation test system combined with the real-time AE monitoring system, were conducted a series of dynamic cyclic loading tests on the flawed plate sandstone. The results indicated that the dynamic frequencies and dip angles had significant effects on the deformation, strength and failure mode of specimens. Additionally, the degree of specimen failure decreased with the increase of disturbance frequency under the same inclination angle; along with, the most severe failure occurred when the inclination angle was 45 ° under the same disturbance frequency. The main failure mode of specimens was shear failure from the distribution of AF-RA. Meanwhile, for specimens with small angles (30 °, 45 °) and low frequencies (0.1, 0.3 Hz), the failure types were more complex (tensile-shear mixed failure). On the other hand, the AE characteristics mainly included three stages: I-initial cycle, II-stable development, and III-damage & failure. The CNT and ENE were greatly influenced by the disturbance frequency and inclination angle. In addition, the b-value decreased and fluctuates violently, and the strength of the samples was reduced as the loading frequency decreased. The specimens with smaller inclination angles had larger internal activity scales and more frequent damage activities with smaller b-value. Furthermore, Correlation dimension Dm was positively correlated with the change of disturbance frequency, and it was smaller when the inclination angle was 45 °.

Role of confinement in coseismic pulverization: Testing the rock record of rupture directivity on the San Jacinto fault, Southern California

The San Jacinto fault juxtaposes Pleistocene Bautista Formation sediments against Cretaceous tonalite near Anza, California. While the tonalites show typical features of pulverized fault zone rocks on the NE side of the fault, the weakly consolidated Bautista Formation shows evidence of pulverization at a depth of 120 m, yet only background level deformation at 70 m, consistent with the expectation that a minimum confining pressure is required to initiate pulverization in poorly consolidated sediments. We test this hypothesis by simulating pulverization using a modified Split Hopkinson Pressure Bar apparatus, in which dry and wet sediments are subjected to up to three repeated dynamic triaxial compressive load cycles. We suggest unconsolidated sediments require a minimum confining pressure under axial compression to initiate pulverization and multiple seismic cycles to reach the observed fracture densities. Companion experiments conducted on Ottawa sand suggest sub-grain scale inelastic deformation in the bulk (i.e., not localized in deformation bands) occurs preferentially at high strain rates. Furthermore, the compressive origin of sediment pulverization, along with evidence of tensile fragmentation in cross-fault tonalite, supports a preferred northwest rupture direction along the southern section of the San Jacinto fault.

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.

Dynamic compression study of seawater sea sand concrete incorporated with expansive agents and glass fibre

Seawater sea sand concrete (SSSC) is an eco-friendly protection material with better development prospects than other cementitious composites. There are many projects facing dynamic compressive load during construction and operation. Therefore, it is important to explore an SSSC with excellent dynamic compression performance. In this study, alkali-resistant glass fibre (GF) was used to enhance the performance of SSSC and expansion agent (EA) was introduced to improve the interface of cement slurry. The results show that the slopes of the relationship between DIF and strain rate of F1EA6, F1EA0 and F0EA6 are 12.6%, 8.4% and 6.7% higher than that of F0EA0, respectively, which indicates that GF and EA have a more significant strain rate effect on the dynamic compression performance of SSSC. In addition, through introducing the fineness modulus of residue (MR) and scanning electron microscopy (SEM) observation to analyse the failure mode of the specimen, it further proves that GF and EA have a synergistic effect on dynamic compressive strength. This study put forward some guidelines for the future research direction of impact resistance of SSSC structure.

Response of the ultra high performance concrete under dynamic compressive loading

Ultra high performance concrete is a modern cementitious material which exhibits excellent mechanical properties such as damage tolerance, fracture toughness and durability. These features make this materials suitable for wide range of applications where is the material subjected to different modes of loading and different loading rates.This paper deals with measurement of the Ultra high performance concrete reinforced with steel fibres in quasi-static compression mode of deformation and two elevated strain rates using split Hopkinson pressure bar. The results of the measurement show high increase of the mechanical properties with elevated strain rate.

Experimental study of off-axis compression behaviour in dynamic loading: The open hole effect

The effect of the open hole on the behaviour of carbon fibre reinforced polymer composites (CFRP) under compressive dynamic loading was investigated. To this end, two different set-ups (quasi-static and dynamic) for compression loading were developed. The un-notched plain woven CFRP (AS4 fibres and 8552 matrix) studied in this work was characterized in terms of apparent strength at different off-axis angles at compression loading. The maximum stress criterion was found to be the model which better represents the transverse-shear failure points of the woven composite. Later the effect of the open hole in similar samples were studied, concluding that the hole effect has more impact on the strength for samples with the fibre align with the load. A modification of the Lekhnitskii theory has been proposed in order to take into account the non-linearity of the material and to unveil its role in open hole specimens.

Simulating the mechanical stimulation of cells on a porous hydrogel scaffold using an FSI model to predict cell differentiation.

3D-structured hydrogel scaffolds are frequently used in tissue engineering applications as they can provide a supportive and biocompatible environment for the growth and regeneration of new tissue. Hydrogel scaffolds seeded with human mesenchymal stem cells (MSCs) can be mechanically stimulated in bioreactors to promote the formation of cartilage or bone tissue. Although in vitro and in vivo experiments are necessary to understand the biological response of cells and tissues to mechanical stimulation, in silico methods are cost-effective and powerful approaches that can support these experimental investigations. In this study, we simulated the fluid-structure interaction (FSI) to predict cell differentiation on the entire surface of a 3D-structured hydrogel scaffold seeded with cells due to dynamic compressive load stimulation. The computational FSI model made it possible to simultaneously investigate the influence of both mechanical deformation and flow of the culture medium on the cells on the scaffold surface during stimulation. The transient one-way FSI model thus opens up significantly more possibilities for predicting cell differentiation in mechanically stimulated scaffolds than previous static microscale computational approaches used in mechanobiology. In a first parameter study, the impact of the amplitude of a sinusoidal compression ranging from 1% to 10% on the phenotype of cells seeded on a porous hydrogel scaffold was analyzed. The simulation results show that the number of cells differentiating into bone tissue gradually decreases with increasing compression amplitude, while differentiation into cartilage cells initially multiplied with increasing compression amplitude in the range of 2% up to 7% and then decreased. Fibrous cell differentiation was predicted from a compression of 5% and increased moderately up to a compression of 10%. At high compression amplitudes of 9% and 10%, negligible areas on the scaffold surface experienced high stimuli where no cell differentiation could occur. In summary, this study shows that simulation of the FSI system is a versatile approach in computational mechanobiology that can be used to study the effects of, for example, different scaffold designs and stimulation parameters on cell differentiation in mechanically stimulated 3D-structured scaffolds.

Characterization of dynamic confinement response of potting materials at different strain rates and temperatures

A Kolsky compression bar was modified with an instrumented confining tube for characterizing dynamic confinement response of materials at various strain rates. A thin film polyvinylidene fluoride (PVDF) force transducer was designed and integrated to the confining tube for direct in-situ measurement of confining pressure when the specimen is subjected to dynamic axial compressive load such that the mean stress-volumetric strain response of the specimen material is able to be determined. An environmental chamber was also implemented to the Kolsky compression bar for characterizing dynamic confinement response of materials at different environmental temperatures. After careful calibration of the instrumental confining tube, five different potting materials (EPON 828, EPON 828 filled with glass microballoons (GMBs), Sylgard 184, Sylgard 184 filled with GMBs, and expanded polystyrene (EPS) foam) were characterized with the modified Kolsky compression bar at different strain rates and environment temperatures. The effects of strain rate and temperature on the mean stress-volumetric strain response were determined for all five potting materials. Experimental uncertainties were also presented.

Automatic detection of spinal injuries under dynamic compressive loading using high-speed cine-radiography.

Every year, new cases of individuals suffering from traumatic spinal injuries are detected. Advances in numerical models have allowed for the understanding of the damage caused by trauma and its impact on the patient's life. However, the kinematics and dynamics of vertebral fracture formation from its point of origin to the speed of propulsion of the fragments remain unknown. This is mainly due to the lack of data that essentially includes high-speed videos, load and displacement measurements during experimental tests reproducing spinal traumatic loading conditions. This lack of data can be addressed by the analysis of X-Ray images of animal specimens acquired during the traumatic spinal injury formation process. Thus, the purpose of this study was to develop an approach to automatically detect and track in vitro vertebral fractures using high-speed cine-radiography imaging. Four segments of porcine thoracolumbar vertebrae were dynamically compressed using a servo-hydraulic test bench. The compression process was filmed with a custom high-speed cine-radiography device, and the imaging parameters were optimized based on the physical properties of vertebrae. This paper demonstrates the feasibility of using high-speed cine-radiography imaging in this way, combined with an image processing pipeline to allow automatic documentation of the fracture's appearance and its evolution in the vertebra over time.Clinical Relevance- The proposed method will provide helpful information for proper handling of traumatic spinal injuries.

Machine learning/finite element analysis - A collaborative approach for predicting the axial impact response of adhesively bonded joints with unique sandwich composite adherends

Despite the increasing usage of adhesively bonded joints (ABJs) in various industries, optimization of their bond strength in a cost-effective manner remains a challenging task, particularly when complex loading scenarios such as static and dynamic compressive loadings are considered. The task becomes even more challenging in bonded joints with sandwich composite adherends. This study focuses on the performances of double-strap ABJs configured by unique sandwich composite adherends, carbon fiber-reinforced plastic straps, and a room-cured structural epoxy resin under axial impact loading. A Finite Element-Cohesive Zone (FE-CZ) model is developed to simulate the response of the joints, and its integrity is validated against the experimental tests at three impact energy levels. The model is used to simulate the response of various ABJ configurations under axial impact loading, taking into account 13 material, geometrical, and testing-related parameters that influence joint strength, thereby generating 410 data sets. Subsequently, three Machine Learning (ML) models, including deep neural networks and genetic evolution (i.e., genetic programming and genetic algorithms) are developed and trained by the data sets to predict the ABJs load-bearing capacity. The ML models explore the relationship between the design parameters and the joint's ultimate load-bearing capacities, leading to the development of cost-effective and accurate empirical equations, and optimized joint configurations.

Static and dynamic compression load tests of conically connected, screw fixed dental abutment

The basis of the long-term success of dental implants is the mechanical stability of the implant and the superstructure anchored in it. In order to investigate the mechanical behaviour of the conical connection in implant-abutment units, static and dynamic load tests were performed with different conical angles and various Grade 4-5 titanium implant materials. The assembled units were mounted in self-developed loading machine and in an Instron ElectroPuls E3000 fatigue machine. For static loading, the samples were loaded with a force from 0 N to 500 N in steps of 100 N. For dynamic loading, the samples were loaded for 30,000 cycles with a force of 250 ± 150 N. In case of static testing, the compression caused by the load was measured in both horizontal and vertical directions, while in the case of dynamic fatigue, only horizontal deformation was defined. In both cases, the drive-out (reverse) torque values of the fixing screws were determined after loading. No significant differences were found between the tested materials in the reverse torque after the static load, however, significant differences were shown with regards to the alterations in cone angle (p < 0.001). After dynamic loading, significant differences (p < 0.001) were also observed between the reverse torques of the fixing screw in different angles. The static and dynamic test results showed the same tendency: under the same load conditions, the conical angle value of the implant-abutment connection revealed significant differences in the loosening of the fixing screw. In summary, it is recommended to use higher conical angle connection to avoid larger deformations in lengths and diameters of the implant at the connection and essential torque reduction of the fixing screw. Our results may contribute to the understanding of the long-term success of dental implants.

Dynamic mechanical properties and failure behaviors of brittle rock materials with a tunnel-shaped opening subjected to impact loads

Since the surrounding rocks of underground tunnels are frequently suffered from the dynamic disturbance of mechanical percussion drilling and explosive blasting, it is significantly meaningful to investigate the mechanical properties and failure behaviors of rock material with a tunnel-shaped opening under dynamic loads. In this work, seven groups of prismatic samples, including the intact samples and the samples with a circular opening of three kinds of diameters, a square opening, a horseshoe-shaped opening and a D-shaped opening, were prepared for dynamic compressive loading. The results show that the prismatic specimens satisfy the stress uniformity condition in impact tests using SHPB testing system with a bar diameter of 50 mm. The weakening effects of the existed openings on the dynamic compressive strength, elastic modulus and peak strain of rocks are closely associated with the size and shape of opening and the loading direction. Based on the energy parameters of the samples, the dissipated energy density of each group of samples can be solved. The failure degree of the samples characterized by dissipated energy density and fractal dimension are in good agreement. Besides, the failure mode of the intact specimen belongs to splitting tensile failure, while that of the pre-holed specimens can be classified as shear-dominated failure due to the coalescence of the openings and the shear cracks occurring along the diagonals of the specimens. The test results provide some insights into the mechanical behavior of rock materials under dynamic loads and lay an important theoretical foundation for support design and rock disaster prevention of underground tunnel.

Response of Topological Soliton lattice structures subjected to dynamic compression and blast loading

A novel topological soliton lattice (TSL) unit cell with fascinating behavioral characteristics is developed. Lattice structure as well as the sandwich composite panels are both constructed. Numerical simulation is utilized to simulate the dynamic compression and blast behavior of the proposed structures considering the rate-dependent properties, elastoplastic response and nonlinear contact. Mooney–Rivlin (MR) hyperelastic constitutive model and Generalized Maxwell model are used to model the TSL structure, and Johnson–Cook material model is implemented to model the plate material. The numerical model is validated by comparing with the experimental results. A series of parametric studies are conducted to gain insight into the effects of loading velocity, number of core layers, equivalent TNT loads and panel thickness on the dynamic mechanical behavior of the TSL lattice and sandwich structures. Testing results indicated that the proposed TSL lattice possessed an attractive mechanical behavior, which was relevant to the specific geometric parameters and loading conditions. The proposed novel lattice would expand the design space for the development of future materials with customized response characteristics.

Study on the Mechanical Behavior of a Dual-Density Hybrid Lattice Structure under Quasi-Static and Dynamic Compressions.

The dual-phase lattice structure composed of the matrix phase (MP) and the reinforcement phase (RP) is a novel hybrid lattice showing excellent energy absorption ability. However, the mechanical behavior of the dual-phase lattice structure under dynamic compression and the enhancement mechanism of the reinforcement phase have not been widely studied with the increase in compression speed. Based on the design requirements of dual-phase lattice materials, this paper combined octet-truss cell structures with different porosities, and the dual-density hybrid lattice specimens were fabricated via the fused deposition modeling technique. Under quasi-static and dynamic compressive loadings, the stress-strain behavior, energy absorption capacity, and deformation mechanism of the dual-density hybrid lattice structure were studied. The results showed that the quasi-static-specific energy absorption of the dual-density hybrid lattice structure was significantly higher than that of the single-density Octet lattice, and with the increase in compression strain rate, the effective specific energy absorption of the dual-density hybrid lattice structure also increased. The deformation mechanism of the dual-density hybrid lattice was also analyzed, and the deformation mode changed from an inclined deformation band to a horizontal deformation band when the strain rate changed from 10-3 s-1 to 100 s-1.