Dynamic Loading Modes Research Articles

Laboratory study of the behaviour of grouted cable bolts under static and dynamic axial loading

As a typical roof-supporting system of tunnels, Cable bolts are subjected to static and dynamic loading conditions caused by ground movements and mining activities. As mining goes deeper, the chance of undetermined ground stress concentrations increases and subsequently, the probability of sudden unexpected failures such as rock bursts increases. Many studies have been carried out to simulate the axial loading condition of the tendons, especially cable bolts, under static and dynamic loading modes; however, it barely can be seen that both behaviours have been studied and compared simultaneously. From other points of view, although research has been conducted on Barrel and Wedge and load-bearing plates, these components have hardly been considered together in axial loading studies. In this laboratory study, a new pullout testing mechanism has been introduced, which is capable of implementing axial loading of cable bolts in both static and dynamic loading conditions. In addition, in a parametric study, the role of bulbs of the cable bolts as well as barrel and wedges on the load-bearing capacity of the anchors have been examined. The bond between cable bolts and grout material in the bulbed cables behaves almost 30% stronger in static and 40% stronger in dynamic tests in comparison with plain cables. In general, the required pullout energy in dynamic tests was 25-50% less than in static tests.

Adaptive force tracking control of electrohydraulic systems with low load using the modified LuGre friction model

The force tracking performance of controllers is seriously degraded by the complex friction behaviors when the electrohydraulic system applies low load. The existing LuGre model is employed in the motion control system with the known trajectory. In this work, a modified LuGre model combined with a zero-velocity crossing window is established to address the lag issue and model oscillation in force control system. Then, the Stribeck curve in the friction model is accurately obtained using a fast measurement method, and the impact of friction parameters on the accuracy of the LuGre model is analyzed. Next, an adaptive friction compensation control scheme is proposed for the electrohydraulic system with low load using the modified LuGre model to compensate for dynamic friction behavior and improve the force tracking performance. The uncertain friction parameters are tuned online to reduce the force error of the low-velocity region via the derived adaptive law and a dual-observer. The disturbance observer is effectively integrated to reduce the negative influence of unconsidered dynamics. Finally, comparative experiments are conducted to verify the effectiveness of the proposed controller in static and dynamic loading modes.

Research changes in the properties of butadiene-nitrile rubber under various aging conditions

This article represents the results of a study of changes in the properties of vulcanizates based on BNR-18 butadiene-nitrile rubber containing as stabilizers the experimental spatially hindered phenols Stafen, CO3, CO4, and industrial antioxidant 6PPD, after accelerated aging (100°C 96 h) and aging under full-scale exposure in extreme climatic conditions of the Republic of Sakha (Yakutia) during 2 years. In winter, the air temperature reached—48°C, in summer—+36.1°C. It is shown that the experimental sterically hindered phenols more effectively under natural exposure conditions. They are characterized by the most stability in terms of strength throughout the entire exposure period. Under conditions of accelerated aging, the vulcanizate containing the industrial antioxidant 6PPD is characterized by the greatest stability of physical and mechanical properties. According to the viscoelastic characteristics obtained in the dynamic loading mode, the contribution of the presented stabilizers in maintaining resistance to temperature and deformation effects compared with unstabilized rubber is confirmed.

The rationale for the loading modes of diesel engines for the diagnosis at unsteady load

To increase the reliability of diagnosing tractor engines, a dynamic loading mode is proposed under bench conditions. The loading modes are substantiated from the point of view of diagnostics of the input action and the most informative mode of engine operation.

The mechanical properties of high strength Al alloy sheet under quasi-static-dynamic loading

To investigate the mechanical properties of high strength Al alloy, the AA2024 was selected and conducted the uniaxial tensile tests at room temperature under different loading modes, namely pure quasi-static (QSD) loading mode, pure dynamic loading mode and quasi-static-dynamic loading mode. The mechanical properties such as yield stress (YS), ultimate tensile stress (UTS), total elongation and strain rate sensitivity were compared. The results shown that the UTS under QSD loading mode is larger than that of quasi-static and pure dynamic loading mode, and dependent on prestrain levels. However, the YS at pure dynamic loading mode is less than that of QSD loading mode at prestrain of 10% but larger than that of prestrain of 6%. In addition, the QSD loading mode would further improve the total elongation of AA2024 compared to the elongation enhancement under pure dynamic loading mode. Finally, the variation of strain rate sensitivity under different loading modes was analyzed to explain the evolution of tensile properties of AA2024.

Comparison of porcine and human adipose tissue loading responses under dynamic compression and shear: A pilot study

Understanding the mechanical properties of human adipose tissue, and its influence on seat belt-pelvis interaction is beneficial for computational human body models that are developed for injury prediction in the vehicle crashworthiness simulations. While various studies have characterized adipose tissue, most of the studies used porcine adipose tissue as a surrogate, and none of the studies were performed at loading rates relevant for motor vehicle collisions. In this work, the mechanical response of human and porcine adipose tissue was studied. Two dynamic loading modes (compression and simple shear) were tested in adipose tissue extracted from the human abdomen and porcine back. An Ogden hyperelastic model was used to fit the loading response, and specific material parameters were obtained for each specimen. Two-sample t-tests were performed to compare the effective shear moduli and peak stresses from porcine and human samples. The material response of the human adipose tissue was consistent with previous studies. Porcine adipose tissue was found to be significantly stiffer than human adipose tissue under compression and shear loading. Also, when material model parameters were fit to only one loading mode, the predicted response in the other mode showed a poor fit.

Experimental study on dynamic mechanics and energy evolution of rubber concrete under cyclic impact loading and dynamic splitting tension

To comprehensively explore the mechanical damage and energy evolution of rubber concrete under different dynamic loading modes, the dynamic mechanical experiments of rubber concrete under four loading modes were carried out by using the split Hopkinson pressure bar (SHPB) system. The main tests were the single impact compression, cyclic impact compression with constant load, cyclic impact compression with variable load, and dynamic splitting tension based on the splitting principle of Brazilian disc (BD). The failure modes, stress waves, stress–strain curves, strength, deformation, and energy evolution characteristics of rubber concrete under different test methods were analysed. Under impact compression, the macroscopic cracks of the specimens first appeared on the local weak surface of the edge and propagated with the increase of impact pressure and impact times. Under dynamic splitting, the fracture of specimens began from the “initial compression damage zone (ICDZ)”, and extended to the center of the specimen along the force direction due to the action of stress concentration. The change of the wave impedance of the specimen determined the variation characteristics of reflected and transmitted waves, which reflected the cumulative damage evolution of the specimen in the process of cyclic impact. When the cyclic impact was carried out many times under the critical impact load, the strength and deformation showed the phenomenon of “strengthening at first and then weakening” and “decreasing at first and then increasing” respectively. The evolution curves of reflected energy ratio and absorbed energy ratio were complex and opposite. The evolution curves of specific energy absorption and absorbed energy ratio can be divided into three stages, which can effectively reflect the damage change of the specimens under different impact loads.

ПРОГРАММА ЭКСПЕРИМЕНТАЛЬНЫХ ИССЛЕДОВАНИЙ НЕСУЩЕЙ СПОСОБНОСТИ БЕЗБАЛОЧНЫХ ПЛИТ НА ПРОДАВЛИВАНИЕ ПРИ ДИНАМИЧЕСКОМ НАГРУЖЕНИИ. КОНСТРУКЦИЯ ОПЫТНЫХ ОБРАЗЦОВ

this article presents a program for experimental research of the behavior of reinforced concrete slabs when forced through in static and short-term dynamic loading modes. At hazardous production facilities, there is always an increased probability of emergency situations of disaster nature that lead to explosions and are characterized by a sharp increase in the front, a short duration and a wave character. Taking into account the placement of complex technological processes in buildings, it is now necessary to implement “flexible” space-planning solutions, for example, the use of girderless floors. The need to perform these studies is also due to the lack of methods and regulatory documents that regulate the calculation of the penetration of unbalanced monolithic slabs under dynamic loading. The purpose and objectives of this program are: to assess the influence of the thickness of the slab part of samples and the concrete class on the strength and crack resistance of elements, to obtain new experimental data describing the processes occurring in concrete and reinforcement, to identify patterns of destruction of samples. The test was carried out on a test stand based on a copra rig. The choice of sizes of prototypes is determined by the technical characteristics of this installation, the tasks of the experiment, the possibilities of manufacturing and testing models, and obtaining sufficiently reliable values of the parameters under study during testing. Twelve samples were tested for short-term dynamic loading and four samples for static loading. The following parameters vary: the concrete class (B15 and B20) and the thickness of the slab part of the sample (100 mm and 120 mm). The paper describes the dimensions, reinforcement, concrete classes of the studied samples, the sequence of work in the manufacture of samples, taking into account the installation of load cells. The result of this work is the development of a test method for prototypes.

Dynamic Compression Performance of Reaction Sintering SiC/B<sub>4</sub>C Composite

SiC/B4C composite was obtained using the reaction sintering method with Si infiltration, which exhibited excellent mechanical properties. The dynamic compressive response was investigated using a Split Hopkinson pressure bar at high strain rates ranging from 0.4×103 to 1.2×103 s-1. The results show that the dynamic strength of the SiC/B4C composite obtains a peak value at a strain rate of 1000/s, while its strain increased continuously with increasing strain rate. The dynamic loading mode of SiC/B4C composite exhibited three deformation regions, including an inelastic deformation region, rapid loading region and failure region. The dynamic failure mode of SiC/B4C composite depended upon the strain rate.

Comparative Analysis of Fatigue EnergyCharacteristics of S355J2 Steel Subjected toMulti-Axis Loads.

In this study, a novel test system for estimating bending and torsion fatigue under selectable kinematic and dynamic loading modes was constructed. Using S355J2 steel specimens, a series of tests were conducted to determine material sensitivity to different load paths and loading modes. The experimental results were supplemented with the results of numerical analyses, on the basis of which the components of strain and stress tensors for subsequent analyses were determined in the entire working part of the specimen. An original method for determining specific strain energy components was used. The experimental results showed the grouping of data according to the mode of loading chosen. This could signify that the selected fatigue models are sensitive to certain loading scenarios. We performed in-depth data analysis and complex numerical simulations, formulating likely explanations for the observed effect.

Numerical modeling of nonlinear dynamic and static compression of the metal mesh

Simulation of elastoplastic compression of a symmetric fragment of a bundle of woven steel grids was carried out. The simulation was carried out under static and dynamic loading modes in ANSYS and ANSYS LS-DYNA computing systems. A porous mesh package is formed by overlaying the layers on top of each other while maintaining the directions of wires. Such a packet has a quasiperiodic structure; therefore, a certain symmetric fragment can be distinguished. The compression was carried out by a pair of absolutely rigid plates moving symmetrically towards each other. In the calculations, a multilinear plasticity model with isotropic hardening was used. The diagram of static deformation of the material was used which was obtained experimentally. The calculations were carried out according to the algorithm of a perfect symmetric contact of bodies without friction and with friction. The dynamic loading of a fragment of the mesh packet was carried out at a constant speed. The characteristics of the pulse and the loading rate correspond to those observed in previous experimental studies. The dynamic strain diagram was assumed to be similar to a static one with an increased yield strength. Calculations showed that in all loading modes there is a high level of internal stresses, and complex inhomogeneous stress-strain state. We investigated two factors that could cause differences in the behavior of the curves of deformation of a porous medium - the finite length of the acting pulse and the differences in the dynamic and static compression diagrams of the initial mesh material. The main influence on the dynamic behavior of a fragment of a porous packet of a steel mesh is exerted by the dynamic properties of the wire material. The strain curves of the porous fragment qualitatively change in accordance with the behavior observed in static and dynamic experiments. The final duration of the loading pulse and the friction between the wires for this type of mesh do not have a significant effect. The numerical dependences of the relative area of the normal and lateral through sections of the symmetric fragment of the grid packet on the compression deformation are obtained.

The Effect of Loading on the Diffusivity of Chlorides in Mortar.

This study focuses on the effect generated by a compressive load, in the range 15%–60% of the ultimate load (Fu), in the chloride penetration rate of cement-based materials. The modifications produced in the microstructure influence the transport properties, and, thus, the validation of several interesting parameters, such as, the load value and the loading time, including both static and dynamic loading modes, was evaluated. This analysis was performed by impedance spectroscopy (IS), a non-destructive technique that allowed, after the appropriate modeling analysis, the assessment of the resistivity of the sample, a parameter that has been correlated to the diffusion coefficient in a previous investigation. The experimental arrangement was designed to allow the recording of the impedance spectra under the effect of a compressive load and, thus, the real-time monitoring of the chloride diffusivity was provided. An increase in the diffusion coefficient was verified for a load at 60%Fu whereas no variations were obtained for the load fixed at 30%. A relevant difference could be checked if the values were measured once the load was removed, showing the importance of the precise loading stage for the chloride diffusion study.

The dependence of the Taylor–Quinney coefficient on the dynamic loading mode

The efficiency of the thermomechanical conversion, expressed as the Taylor–Quinney coefficient (TQC) is seldom reported in the literature and generally assumed to be equal to 0.9. Moreover, an eventual dependence of this coefficient on the dynamic loading mode has not been investigated so far.This work presents a systematic characterization of the TQC for seven different metals and alloys loaded in dynamic tension, compression and dominant shear. The results show that the TQC varies greatly with the investigated material, instead of its assumed constant value of 0.9. Likewise, until final collapse of the specimen, the overall temperature rise remains quite modest.Moreover, we clearly observe that for commercially pure Titanium, which exhibits an asymmetric mechanical response in tension and compression, the measured TQC values are mode dependent too. Microstructural characterization reveals profuse twinning in compression and shear, as opposed to tension. Twinning is related to heat generation in accord with previous studies.In addition to reporting a wide database of TQC values, this study reveals a new correlation between the thermomechanical characteristics of a material and its deformation micromechanisms, that should find its way into constitutive models.

A Damaged Medium Model for Describing Dynamic Spallation Fracture

The main physical laws of the failure process in structural materials under dynamic loading modes and mathematical models of such processes are considered. To describe dynamic spallation fracture, a version of governing equations of damaged medium mechanics is developed, consisting of three interrelated parts: governing equations describing plastic behavior of the material as a function of the failure process, evolution equations of damage accumulation, and a strength criterion of the damaged material. A methodology for determining material parameters of kinetic equations of damage accumulation, based on minimizing the quadratic deviation between theoretical and experimental data is used. Comparison of the obtained computational results with the experimental data on dynamic spallation fracture in plates during plane impact shows that the present model of damaged medium mechanics adequately describes experimental data and can be effectively used in analyzing dynamic spallation fracture.

Mechanical behaviour of ABS: An experimental study using FDM and injection moulding techniques

Fused deposition modelling (FDM) in contrast to injection moulding was studied to investigate the effect of processing technique on the mechanical behaviour of virgin ABS. FDM parameters were further altered in terms of varying raster angle and gap to further explore the potential of this technique. Results show that an adequate selection of FDM parameters is able to reach mechanical properties comparable to those of injection moulded parts in both static and dynamic loading modes. Here, a negative raster gap proved to be most significant in enhancing mechanical behaviour. A raster angle layup of −45°/+45° proves to offer maximum tensile and impact strength, whereas highest flexural strength was recorded for a 0/90° scaffolding system. In contrast, a positive gap drastically reduces the performance. Dimensional analysis further show no significant alterations of dimensions are to be expected with varying raster angle and gap.

Method for increasing the reliability of transmission bench testing

The paper describes approximation method to the operational conditions of loading tractor transmission on the test bench when reproduction of dynamic loading modes.

Long-term testing of a high-temperature proton exchange membrane fuel cell short stack operated with improved polybenzimidazole-based composite membranes

In this work, the feasibility of a 150 cm2 high-temperature proton exchange membrane fuel cell (HT-PEMFC) stack operated with modified proton exchange membranes is demonstrated. The short fuel cell stack was manufactured using a total of three 50 cm2 membrane electrode assemblies (MEAs). The PEM technology is based on a polybenzimidazole (PBI) membrane. The obtained results were compared with those obtained using a HT-PEMFC stack with unmodified membranes. The membranes were cast from a PBI polymer synthesized in the laboratory, and the modified membranes contained 2 wt.% micro-sized TiO2 as a filler. Long-term tests were performed in both constant and dynamic loading modes. The fuel cell stack with 2 wt.% TiO2 composite PBI membranes exhibited an irreversible voltage loss of less than 2% after 1100 h of operation. In addition, the acid loss was reduced from 2% for the fuel cell stack with unmodified membranes to 0.6% for the fuel cell stack with modified membranes. The results demonstrate that introducing filler into the membranes enhances the durability and stability of this type of fuel cell technology. Moreover, the fuel cell stack system also exhibits very rapid and stable power and voltage output responses under dynamic load regimes.

Dynamic caustics and its applications

For the study of elastodynamic problems of propagating cracks it is necessary to evaluate the dynamic stress intensity factor K d I which depends on the form of expressions for the stress components existing at the running crack tip at any instant of the propagation of the crack and the corresponding dynamic mechanical and optical properties of the material of the specimen under identical loading conditions. In this paper the distortion of the form of the corresponding reflected caustic from the lateral faces of a dynamically loaded transparent and optically inert specimen containing a transverse crack running under constant velocity was studied on the basis of complex potential elasticity theory and the influence of this form on the value of the dynamic stress intensity factor was given. The method was applied to the study of a propagating Mode I crack in a PMMA specimen under various propagation velocities and the corresponding dynamic stress intensity factor K d I evaluated. Also, crack propagation behaviour of notched composites in dynamic loading modes are reviewed and evaluated. A relatively large data base using metal-epoxy particulates, rubber-toughened poly(methyl methacrylate), and Sandwich plates are given. In all cases, a combination of high-speed photography and the optical method of dynamic caustics has been used. Results on the dynamic crack propagation mode, fracture toughness and crack propagation velocities of several rubber-modified composite models are presented. The composite models studied include specimens with one and/or two ‘complex’ two-stage inclusions, i.e. PMMA round inclusions surrounded by concentric rubber rings, one and/or press-fifting inclusions without rubber interface, all under dynamic loading. In all cases both qualitative and quantitative results were obtained. Also, results on crack propagation mode, crack propagation velocity, stress intensity factors and on the influence of the sandwich phases on crack propagation mode are presented.

Reduction of axial plate screw force in a cortical bone static and dynamic loading mode

Reduction of axial plate screw force in a cortical bone static and dynamic loading mode

Dynamic propagation and arrest measurements by the method of caustics on overlapping skew-parallel cracks

In this paper the quasi-static and dynamic behaviour of two skew-parallel and unequal edge cracks in a brittle material, namely PMMA, was investigated. The study was undertaken by using the optical method of caustics in combination with a high-speed Cranz-Schardin camera for recording the various steps of the statically or the dynamically propagated cracks. From the whole study it was deduced that, for the case of the quasi-static loading and for all geometrical configurations of cracks, only the longer crack was propagated, while the shorter crack remained stationary. The propagation path of the longer crack curved towards the opposite edge crack. Both edge cracks propagated simultaneously only under the dynamic loading mode and under certain favourable combinations of the geometrical configurations of the cracked specimen. Both edge cracks curved, under quasi-static loading and strong tendency for crack arrest phenomena was observed. The values of the crack propagation velocity and the stress intensity factors for both cracks were determined and were found to be larger for the dynamic than for the quasi-static loading case.