Increase Of Load Amplitude Research Articles

Performance of metal circular tube under different loading amplitudes and dynamic resistance-yielding mechanism

As coal mining depth increases, the characteristics of “high ground stress, high ground temperature, high osmotic pressure, and mining disturbance” become increasingly pronounced, posing new challenges to the stability of the surrounding rock roadway. Amplitude is a key parameter affecting disturbance strength. A cyclic loading and unloading experiment was conducted under different amplitudes to explore the effect of metal circular tubes, used as energy-absorbing components, on the protection performance of anchor bolt tails. This experiment further revealed the competitive protection mechanism of the metal circular tube, termed “resistance - yielding”. The research results indicate that the metal tube incurs damage and accumulates it with the increase of loading amplitude in the pre-peak stage, leading to a decrease in its peak load. The metal tube absorbs external energy robustly through its elastic-plastic deformation. In the platform stage, a high amplitude load causes the peak load displacement to increase and its stable energy-absorbing stroke to decrease. Plastic energy dominates the main position of energy absorption, and the metal circular tube forms a dynamic competitive relationship of “resistance-yielding” with external stresses. Throughout the entire energy absorption process, the total energy absorption decreases with the increase of amplitude. The research results investigate the effect of amplitude on the performance of metal circular tubes and demonstrate the feasibility of applying metal circular tubes as energy-absorbing members at the end of anchor rods, which can provide theoretical guidance for the prevention of disaster accidents in mines caused by disturbances.

Lateral performance of mortise-tenon jointed frames in multi-story traditional heavy timber structures: Mechanism and quantification

This study isolated and quantified the lateral load-resisting mechanism of mortise-tenon jointed frames in multi-story traditional heavy timber structures. By decomposing the lateral performance of the mortise-tenon jointed frames, three rocking frame specimens and a moment-resisting frame specimen were half-scaled designed. Lateral resistance from timber columns and mortise-tenon joints was directly obtained by reversed cyclic loading tests, respectively, and was compared to quantify the mechanism of the mortise-tenon jointed frames in different stories. Characterized models were proposed for the lateral resistance from the columns and joints, respectively. A model-based parametric study was further conducted to indicate the influence of the column height and diameter on the mechanism of the mortise-tenon jointed frames. Test results showed the columns dominated both in the lateral load-resisting capacity and energy dissipation capacity of the frames at small drift, and the columns still contributed over 50% of those capacities before a drift of 10% with the increase of loading amplitude. The characterized models well captured the evolution features of the load–displacement curves of the tested specimens. The parametric study indicated that by increasing 30% of the column height, the lateral load contribution of the mortise-tenon joints ranged from 60% to 90% at a drift of 12%. Moreover, a decrease of 30% in the column diameter led to a significant drop in the load-resisting capacity and deformability of the columns, making the mortise-tenon joints dominate in the lateral capacity of the frames after a drift of 8%.

Influence of support interface on the lateral performance of rocking columns in traditional Chinese timber structures

This study investigates the influence of support interface on the lateral performance of rocking columns in traditional Chinese timber structures. Six half-scaled timber column specimens, characterized by stone bases or timber bases, were reversed cyclically tested. Typical damage modes were identified, the load–displacement curves of the specimens were evaluated and compared with those of rigid rocking bodies. Theoretical analysis was further conducted based on a trilinear model. The experiments indicated that with the decrease of support stiffness, the damage mode of timber rocking columns shifted from slight parallel to grain deformation at column bottom to significant perpendicular to grain deformation at timber beams. The support stiffness significantly influenced the lateral performance of timber rocking columns. The peak load of a column resting on a stone base was about 80% of that of corresponding rigid rocking body, the column’s hysteretic loops overlapped each other with strength degradation coefficients greater than 0.95. However, with softer timber beams as support, the peak load of a column was reduced to 46% of that of corresponding rigid rocking body, the column’s hysteretic curves prominently pinched and the strength degradation coefficient decreased up to 0.1 with the increase of loading amplitude. The model-based theoretical analysis well captured the load–displacement curves of timber rocking columns on stone bases, and it further indicated when calculating the load–displacement relationship of timber rocking columns on timber beams with lower support stiffness, the local compression effect and hardening effect perpendicular to grain should be considered.

Improving conductivity and self-sensing properties of magnetically aligned electroless nickel coated glass fiber cement

The nickel coated glass fiber (Ni-GF) cement (NGFC) holds promise for self-sensing concrete structure due to its improved conductivity and corrosion resistance. This paper is aimed at evaluating the conductivity and self-sensing properties of preferentially orientated NGFC, which was prepared by the magnetic field (MF) induction. The microstructure of electroless Ni-GFs and their arrangement characteristic in cement were observed by optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The anisotropic conductivity and self-sensing properties of as-prepared composites were measured by four-electrode method. The results indicate that the Ni-GFs with uniform nickel coating layer in the as-fabricated composite have an excellent alignment effect under the MF induction. When the Ni-GF content is 2.62 vol%, the composite exhibits maximum anisotropy. The order of the electrical resistivity and percolation thresholds of NGFC is: parallel to MF < without MF < perpendicular to MF. Under the cyclic compression load, the NGFC parallel to MF shows the optimum self-sensing properties. With the increase of loading amplitude and decrease of loading rate, the maximum sensitivities of the as-prepared composite at all directions almost increase linearly. Under the failure compression load, the conductivity of as-prepared composites parallel to MF show a steadier and higher self-sensing response.

Experimental study on seismic behavior of the damage-control steel plate fuses for beam-to-column connection

Adoption of replaceable damage-control steel plate fuses at the intended location of beam-to-column connection is a potential solution for achieving seismic resilient steel structures. Different from the previous design concept, in this study, buckling of the plate fuse is made full use of to avoid excessive strength increase and also works as a visible damage indicator. Seismic behavior of the proposed damage-control fuses for the beam-to-column connection is studied in detail. Six fuse specimens are designed and experimentally investigated for various fuse dimensions and different loading protocols. Buckling under compression and eventual fracture under tension is the typical failure pattern. The obtained hysteretic curve of the fuse exhibits the feature of asymmetry, with tensile strength larger than compressive strength and the difference becoming larger with the increase of loading amplitude. Different cyclic loading protocols have a greater influence on the ductility than the maximum strength. The compressive strength of the fuse is theoretically estimated, which gives fairly good agreement with the test results. All the fuse specimens can reach the loading amplitude of 5% effective length without fracture. The maximum strength of the fuse degrades with the progress of out-of-plane deformation. The out-of-plane deformation of the fuses could be treated as a visible indicator for determining whether or not to replace the damaged fuse.

Discrete Element Simulation of the Macro-Meso Mechanical Behaviors of Gas-Hydrate-Bearing Sediments under Dynamic Loading

Under the action of dynamic loadings such as earthquakes and volcanic activities, the mechanical properties of gas-hydrate-bearing sediments will deteriorate, leading to a decrease in the stability of hydrate reservoirs and even inducing geological disasters such as submarine landslides. In order to study the effect of dynamic loading on the mechanical properties of hydrate sediments, triaxial compression tests of numerical specimens were carried out by using particle flow code (PFC2D), and the macro-meso mechanical behaviors of specimens were investigated. The results show that the loading frequency has a small effect on the stiffness of the hydrate sediment, while it has a large effect on the peak strength. The peak strength increases and then decreases with the increase in loading frequency. Under the same loading frequency, the peak strength of the hydrate sediment increases with the increase in loading amplitude, and the stiffness of the specimen decreases with the increase in loading amplitude. The maximum shear expansion of the specimen changes with the movement of the phase change point and the rearrangement of the particles. The maximum shear expansion of the specimen changes with the movement of the phase change point and the change of the bearing capacity of the particles after the rearrangement, and the more forward the phase change point is, the stronger the bearing capacity of the specimen in the plastic stage. The shear dilatancy angle and the shear dilatancy amount both increase linearly with the increase in loading amplitude. The influence of loading frequency and amplitude on the contact force chain, displacement, crack expansion, and the number of cementation damage inside the sediment is mainly related to the average axial stress to which the specimen is subjected, and the number of cracks and cementation damage of the sediment specimen increases with the increase in the average axial stress to which the sediment specimen is subjected. As the rate of cementation damage increases, the distribution of shear zones becomes more obvious.

Research on coupled thermo-hydro-mechanical dynamic response characteristics of saturated porous deep-sea sediments under vibration of mining vehicle

The excessive deformation of deep-sea sediments caused by the vibration of the mining machine will adversely affect the efficiency and safety of mining. Combined with the deep-sea environment, the coupled thermo-hydro-mechanical problem for saturated porous deep-sea sediments subject to the vibration of the mining vehicle is investigated. Based on the Green-Lindsay (G-L) generalized thermoelastic theory and Darcy’s law, the model of thermo-hydro-mechanical dynamic responses for saturated porous deep-sea sediments under the vibration of the mining vehicle is established. We obtain the analytical solutions of non-dimensional vertical displacement, excess pore water pressure, vertical stress, temperature, and change in the volume fraction field with the normal mode analysis method, and depict them graphically. The normal mode analysis method uses the canonical coordinate transformation to solve the equation, which can quickly decouple the equation by ignoring the modal coupling effect on the basis of the canonical mode. The results indicate that the vibration frequency has obvious influence on the vertical displacement, excess pore water pressure, vertical stress, and change in volume fraction field. The loading amplitude has a great effect on the physical quantities in the foundation, and the changes of the physical quantities increase with the increase in loading amplitude.

Finite element analysis of the effects of load amplitude and phase on crack initiation location in fretting fatigue

Fretting fatigue is a major form of fretting damage affected by various factors. In this paper, the Ruiz parameter is used to predict the variation in the initiation location of the fretting fatigue crack with the amplitude of load, providing a reference for the study of the initiation characteristics of fretting fatigue cracks. The influence of the phase difference between loads is also considered. Three numerical models are established using ABAQUS for simulation experiments. Four phase difference angles are involved, i.e. 0°, 90°, 180° and 270°. Results indicate that for 0° phase difference, the maximum of initiation parameter K is always observed at the trailing edge of the contact zone (near the loading side of the strain load) with the increase of load amplitude, such that the fretting fatigue crack initiates at the trailing edge. However, for 90°, 180°, and 270° phase differences, the maximum of initiation parameter K shifts from one edge of the contact to the other with the increase of load amplitude. In addition, it is observed that the maximum and minimum initiation parameter K values are obtained for 0° and 180° phase differences, respectively, while the values of K for 90° and 270° phase differences are approximately equal and between those for 0° and 180°.

Dynamic response of the heterogeneous deep-sea sediment with nonlinear gradient modulus to mining machine loading

The deep-sea sediments are usually heterogeneous due to overburden pressure. Excessive deformation of deep-sea sediments caused by mining collector vibration can decrease the stability and reduce the efficiency of the mining system. This study analyzed the dynamic response of the heterogeneous deep-sea sediments under mining collector vibration. First, experiments were conducted to confirm the heterogeneity of deep-sea sediments, and to reveal the relationship that the elastic modulus increases nonlinearly with depth. After that, by predigesting the mining collector vibration to in situ harmonic load, the wave equations were built for solving the dynamic response of deep-sea sediments with nonlinear modulus to mining collector loading. The solution of the equations was verified by comparing it with existing analytical solutions for a homogeneous medium. Based on the verified wave equations, further discussion was conducted on the effects of changing vibration frequency or loading amplitude on the mechanical response of deep-sea sediments. The results indicate that the soil deformation was increased but later decreased with the increase of vibration frequency, and soil deformation increased with the increase of loading amplitude. This study can provide a theoretical rationale for improving the walking efficiency of the mining collector.

Fatigue behavior and prediction model of self-compacting concrete under constant amplitude load and incremental amplitude load

To explore the fatigue fracture behavior of self-compacting concrete (SCC), constant amplitude loading tests and incremental amplitude loading tests were carried out. The experimental results of SCC were obtained and analyzed, including P-CMOD curve, fatigue life, effective crack length, fatigue crack growth (FCG) rate, stress intensity factor (SIF). The results show that the P-CMOD curves of SCC beams follow the unique envelope theory. The fatigue damage of SCC under constant amplitude load can be divided into three stages. In the second stage, cracks grow steadily. The critical SIF is the boundary point between the second and the third stages of fatigue damage. When SIF exceeds the critical SIF, cracks develop rapidly. The first stage of fatigue damage is not obvious for incremental amplitude loading tests. With the increase of load amplitude, there are obvious second and third stages of damage. Except for the maximum load stage, the crack opening rate keeps constant generally. Combined with damage mechanics and fracture mechanics, damage evolution equations of SCC under constant amplitude load and incremental amplitude load were established. The parameters of fatigue damage model based on continuous damage mechanics (CDM) were calibrated by test data, and the predicted results were compared with the experimental results. The results show that the model is sensitive to the first stage of damage. The fatigue damage model based on CDM is more suitable to predict fatigue life for incremental amplitude tests and constant amplitude tests with high cycle. The advantage of this model is that it can be applied to predict fatigue life for different load levels.

A novel t-z model to predict the pile responses under axial cyclic loadings

Jacket foundations are generally used for the offshore wind turbines (OWTs) with water depth more than 30 m. During the service period of OWT, the piles of jacket foundation are mainly subjected to axial cyclic loadings caused by winds and waves. Thus, the axial interaction between the pile and its surrounding soil is the key problem for the design of jacket foundation. In this paper, a novel t-z model was proposed to predict the pile responses under axial cyclic loadings. Model parameters were calibrated through cyclic interface shear tests, and then numerical studies were performed. The results indicate that the cyclic loading modes (two-way, one-way tension and one-way compression) and cyclic load amplitude have obvious effects on the pile axial responses, including accumulated pile displacement, pile axial force, pile-soil interface resistance. It is noted that the displacement of pile accumulates with a fast speed in the one-way cyclic tension mode. With the increase of load amplitude, the maximum residual axial force of pile increases downward significantly except for the shallow depth. The proposed t-z model is appropriate for the assessment of accumulated displacement evolution of jacket foundation at seabed level.

循环动载作用下无砟轨道混凝土裂缝内动水压力研究

无砟轨道是我国高速铁路主要结构形式，根据现场病害调查，底座板与CA砂浆粘结层的裂缝较为普遍，多雨地区其伤损更为严重，出现翻浆冒泥现象。在循环动载作用下，假定裂缝形状为楔形，裂缝边缘张开闭合速度呈正弦规律变化，推导出裂缝在动力荷载作用下因水压缩产生的缝内水压计算式。通过试验验证，分析了裂缝边缘张开闭合速度(加载速度)、裂缝初始张开宽度(荷载大小)对缝内最大附加水压的影响规律。研究表明，加载频率是影响裂纹内部水压力的重要因素。当加载幅值不变时，随着加载频率的增加，裂纹内水压力增大。当加载频率不变时，荷载幅值对裂纹内部水压力有重要的影响。当加载频率不变时，裂纹内部某一点的压力，随着荷载幅值的增加而增大，二者可拟合为一个多项式关系。 The ballastless track is the main structure of the high-speed railway in China. According to the disease survey, cracks of base plate and the CA mortar bonding layer are widespread, and its damage in pluvial region is more serious, with the mud pumping in phenomenon. Under cyclic dynamic load, with the assumption that the crack is wedge-shape and that the velocity of crack edge accords with sine rule, a calculation formula is derived to calculate the internal water pres-sure in cracks under dynamic load due to compression of seam water. The effect of crack edge’s velocity (loading velocity), and crack edge’s initial width (load size) on the additional water pressure and stress intensity factor is analyzed by test. The study shows that load frequency is an important factor to influence water pressure inside the crack. When loading at constant amplitude, with the increase of loading frequency, the internal pressure will increase. When loading at constant frequency, load amplitude has important effect on crack internal water pressure. When loading at constant frequency, crack within a point of stress will increase with the increase of load amplitude, and the two can be fitting for a polynomial.

Deformation and damage mechanisms of a bimodal 12Cr-ODS steel under high-temperature cyclic loading

The present study reports on the high-temperature low-cycle fatigue (LCF) behavior of a ferritic bimodal 12Cr oxide dispersion strengthened steel. The fully reversed strain-controlled LCF tests were conducted at a constant total strain rate with different axial strain amplitude levels. The measured cyclic stress response showed four distinct stages which include instant initial cyclic softening followed by gradual cyclic hardening thereafter continuous linear cyclic softening and finally crack initiation and growth stage. The rate and amount of these stages depend on both strain amplitude and testing temperature. The cyclic stress-strain and strain-life relationships were obtained through the test results, and related LCF parameters were calculated. Microstructural investigations, using electron microscopy, were carried out to shed light on the deformation mechanisms. At 550°C, no appreciable microstructural evolution occurred, which is consistent with the manifestation of Masing behavior. A propensity towards cross-slip and hence the formation of three-dimensional dislocation structures increased with increase in loading amplitude and testing temperature, which assisted in accumulating higher inelastic strain and led to slightly higher cyclic hardening at these conditions. Furthermore, W-enriched Laves phase particles precipitated at grain boundaries. The evolution of cell structures with strain amplitude at 650°C resulted in a small deviation from Masing behavior. The damage studies revealed multiple surface initiated transgranular cracks under higher strain amplitudes and a single surface initiated transgranular crack under lower strain amplitudes. The different stages of the crack path, whose durations depend on the testing conditions, revealed distinct fatigue fracture features.

Experimental Study and Dynamic Modeling of Metal Rubber Isolating Bearing

In this paper, dynamic shear mechanical properties of a new metal rubber isolating bearing is tested and studied. The mixed damping model is provided for theoretical modeling of MR isolating bearing, the shear stiffness and damping characteristics of the MR bearing can be analyzed separately and easily discussed, and the mixed damping model is proved to be an rather effective approach. The test results indicate that loading frequency bears little impact over shear property of metal rubber isolating bearing, the total energy consumption of metal rubber isolating bearing increases with the increase in loading amplitude. With the increase in loading amplitude, the stiffness of the isolating bearing will reduce showing its “soft property”; and the type of damping force gradually changes to be close to dry friction. The features of “soft property” and dry friction energy consumption of metal rubber isolating bearing are very useful in practical engineering application.

Estimation of Temperature Conductivity Coefficient Impact upon Fatigue Damage of Material

In the paper we consider the peculiarities of adhesive wear of cutting tools. Simulation of heat flows in the cutting zone showed that, as thermal conduction and heat conductivity of tool material grow, the heat flows from the front and back surfaces to tool holder will increase and so, the temperature of the contact areas of the tool will lower. When estimating the adhesive wear rate of cemented-carbide tool under the cutting rates corresponding to the cutting temperature of up to 900 °C, it is necessary to take the fatigue character of adhesive wear into consideration. The process of accumulation and development of fatigue damage is associated with micro- and macroplastic flowing of material, which is determined by the processes of initiation, motion, generation, and elimination of line defects - dislocations. Density of dislocations grows with increase of the loading cycles amount and increase of load amplitude. Growth of dislocations density leads to loosening of material, formation of micro- and macrocracks. The heat capacity of material grows as the loosening continues. In the given paper the authors prove theoretically that temperature conductivity coefficient which is associated with heat capacity of material, decreases as fatigue wear grows.

Prediction of liquefaction potential and pore water pressure beneath machine foundations

AbstractThe present research is concerned with predicting liquefaction potential and pore water pressure under the dynamic loading on fully saturated sandy soil using the finite element method by QUAKE/W computer program. As a case study, machine foundations on fully saturated sandy soil in different cases of soil densification (loose, medium and dense sand) are analyzed. Harmonic loading is used in a parametric study to investigate the effect of several parameters including: the amplitude frequency of the dynamic load. The equivalent linear elastic model is adopted to model the soil behaviour and eight node isoparametric elements are used to model the soil. Emphasis was made on zones at which liquefaction takes place, the pore water pressure and vertical displacements develop during liquefaction. The results showed that liquefaction and deformation develop fast with the increase of loading amplitude and frequency. Liquefaction zones increase with the increase of load frequency and amplitude. Tracing the propagation of liquefaction zones, one can notice that, liquefaction occurs first near the loading end and then develops faraway. The soil overburden pressure affects the soil liquefaction resistance at large depths. The liquefaction resistance and time for initial liquefaction increase with increasing depths. When the frequency changes from 5 to 10 rad/sec. (approximately from static to dynamic), the response in displacement and pore water pressure is very pronounced. This can be attributed to inertia effects. Further increase of frequency leads to smaller effect on displacement and pore water pressure. When the frequency is low; 5, 10 and 25 rad/sec., the oscillation of the displacement ends within the period of load application 60 sec., while when ω = 50 rad/sec., oscillation continues after this period.

Liquefaction Potential of Silty Sand Surrounding A Bucket Foundation Under Vertical Vibration Load

To study the liquefaction potential of sand surrounding bucket foundations, centrifuge experiments were carried out. Results have shown that the sand layer around a bucket foundation softens or liquefies under vertical dynamic load when the load amplitude is over a critical value. The liquefaction potential decreased in horizontal direction from the side wall and in vertical direction from the surface of sand layer. The thickness of the completely liquefied sand layer increased with the increase of load amplitude. The affected area which has obvious liquefaction potential is almost the same for a given bucket under different load amplitudes.

Numerical Simulation of Liquefaction Deformation of Sand Layer around Bucket Foundations under Dynamic Loadings

Bucket Foundations under Dynamic Loadings The liquefaction deformation of sand layer around a bucket foundation is simulated under equivalent dynamic ice-induced loadings. A simplified numerical model is presented by taking the bucket-soil interaction into consideration. The development of vertical and horizontal liquefaction deformations are computed under equivalent dynamic ice-induced loadings. Firstly, the numerical model and results are proved to be reliable by comparing them with the centrifuge testing results. Secondly, the factors and the development characteristics of liquefaction deformation are analyzed. Finally, the following numerical simulation results are obtained: the liquefaction deformation of sand layer increases with the increase of loading amplitude and with the decrease of loading frequency and sand skeletonrs strength. The maximum vertical deformation is located on the sand layer surface and 1/4 times of the bucketrs height apart from the bucketrs side wall (loading boundary). The maximum horizontal deformation occurs at the loading boundary. When the dynamic loadings is applied for more than 5 hours, the vertical deformation on the sand layer surface reaches 3 times that at the bottom, and the horizontal deformation at 2.0 times of the bucket height apart from the loading boundary is 3.3% of which on the loading boundary.

Dissipative properties of materials with thermoelastic martensite conversion

Internal friction in metallic materials experiencing a thermoelastic martensite conversion under conditions of a monotonically changing thermodynamic stimulus is determined by two main factors: irreversible processes involving growth of crystals of the new phase, and cyclical motion of the phase boundaries under the action of applied periodic stresses. While the losses caused by irreversible processes decrease with increase in loading amplitude, depending on the type of conversion the amplitude dependence of the background component of internal friction may be of a complex nonmonotonic character, with a maximum in losses at certain oscillation amplitudes. At low amplitudes sections of the boundary unattached to defects perform cyclical motions like membranes, and the losses due to the thermal conversion effect may produce a significant contribution to the overall damping level only at the membrane resonant frequencies. For amplitudes exceeding the critical boundary detachment stress internal friction increases, passes through a maximum, and then decreases anew. The amplitude dependence of internal friction behaves in a similar manner in the process of creation and subsequent collapse of crystals of the new phase in the field of an external periodic load.