Effect Of External Load Research Articles

Combined extension and torsion of hydrogels with chemo-mechanical coupling: Revealing positive poynting effect

In this paper, combined extension and torsion of hydrogel subject to a chemo-mechanical coupled loading is described in the framework of continuum mechanics, where the free energy density consists of the elastic, mixing and chemical contributions. A simplified, closed-form and exactly analytical solution to the mechanical response is obtained, which accounts for the coupling effect of external loading, chemical potential and microstructural parameters, such as crosslinking degree, Flory-Huggins parameter, etc. In particular, the effect of free swelling and microscopic diffusion on deformation of the hydrogel at equilibrium state is discussed, reaching some fundamental conclusions. Negative axial forces are captured, revealing the typical positive Poynting effect where the cylinder tends to elongate on twisting, and an inhomogeneous deformation, induced by torsion, along the radial direction is demonstrated. Furthermore, the dynamic competition between external loading and solvent environment is revealed and investigated, where the direct connection between internal micro-physical parameters and macroscopic deformation is demonstrated. The theoretical results presented in this paper may provide predictions and guidance for the mechanical analysis and design of hydrogel cylinder subject to extension and torsion in a solvent.

The effect of external load to slope stability using slope/w in ft 006, section 61.50, Pulau Pinang

The effect of external load to slope stability using slope/w in ft 006, section 61.50, Pulau Pinang

Nonlinear Slippage of Tensile Armor Layers of Unbonded Flexible Riser Subjected to Irregular Loads

The unbonded flexible riser has been increasingly applied in the ocean engineering industry to transport oil and gas resources from the seabed to offshore platforms. The slippage of helical layers, especially the tensile armor layers of unbonded flexible risers, contribute to the nonlinear hysteresis phenomenon, which is a research hotspot and difficulty. In this paper, on the basis of a typical eight-layer unbonded flexible riser model, the nonlinear slippage of a tensile armor layer and the corresponding nonlinear behavior of an unbonded flexible riser subjected to irregular external loads are studied by numerical modeling with detailed cross-sectional properties of the helical layers, and are verified through a theoretical method considering the coupled effect of the external loads on the unbonded flexible riser. Firstly, the balance equation of each layer considering the effect of external loads is established based on functional principles, and the overall theoretical model of the unbonded flexible riser is set up in consideration of the contact between adjacent layers. Secondly, the numerical modeling of each separate layer within the unbonded flexible riser, including the actual geometry of the carcass and pressure armor layer, is established, and solid elements are applied to all the interlayers, thus simulating the nonlinear contact and friction between and within interlayers. Finally, after verification through test data, the behavior of the unbonded flexible riser under the cyclic axial force, torsion, bending moment, and irregular external and internal pressure is studied. The results show that the tensile armor layer can slip under irregular loads. Additionally, some suggestions related to the analysis of unbonded flexible risers under irregular loads are drawn in the end.

Research on the method of damage theory applied in underground lining structure’s durability

Damage or deterioration may occur in underground lining structures under the effects of external loads, groundwater seepage, and corrosive ions. Consequently, the durability and reliability of the structure can be severely affected. This study first analyzed and summarized the current situation of damage theory used in the durability research of concrete structures and underground. Consequently, the concept of a “deterioration degree function,” which can reflect the degree of damage to a structure, was proposed. Subsequently, the Gurson meso-damage model was analyzed for its application in the durability research of underground structures concerning the theory, formulae, and steps. A type of specimen was designed as an example, wherein the track model of steel corrosion expansion as assumed and deduced, and the numerical calculation of the damage stress was calculated to predict the durable life of the structure. The analysis concept developed in this study can be extended and applied to other research fields with similar durability problems.

Hydrogen blistering and cracking of high-strength pipeline steel welds produced by electrochemical hydrogen charging

Pipeline steel system always faces a challenge of hydrogen embrittlement (HE) not only due to corrosion environments but also because of cathodic protection strategy. Especially in welded joint, heterogeneous microstructures lead to the difference in intrinsic HE resistance for different subzones. However, this aspect was often neglected when external loading was applied during evaluation of the HE. To eliminate the effect of external loading, the hydrogen damage behaviors of X100 pipeline steel weld were investigated only based on electrochemical hydrogen charging and the intrinsic HE resistance of each subzone was explored. The results showed that the HE resistance of the main regions in weld was decreased in order of weld metal, heat affected zone (HAZ) and base metal (BM), with different surface damage modes: the BM had predominantly hydrogen blistering; while others displayed mainly hydrogen cracking. The corresponding features for cross-sectional cracking were intergranular propagation along the pancaked grain boundaries in the BM and trangranular propagation in HAZ. For transgranular cracking propagation, the path first trended to initiate on the {100} cleavage plane, then grew on the {110} slip planes. The intergranular cracking was mainly attributed to the lamellar-structural prior grain boundaries that inherited numerous deformation dislocations during hot rolling of the base metal.

Biomechanical responses on specific load carriage and positive gradient walking: A pilot study

Objectives: Normal load carriage is an inevitable part of military marching tasks. Military tasks are inextricably related to carrying huge loads irrespective of different terrain. Continuous carrying of heavy loads from level ground to uphill gradient may alter kinetic and kinematic responses. Such responses, in the long run, may cause the risk of injury. This study was designed to find out the effects of external load on kinetic and kinematic responses at specific loads and grades (+10°). Materials and Methods: Six healthy Indian soldiers mean (± standard error of mean [SEM]) age 30.5 ± 3.5 years, height 168.7 ± 2.8 cm, weight 73.8 ± 7.08 kg participated in this study, walking on treadmill (Deneb and Polak-speed-1625) at 3.5 kmph for 6 min at 10° inclination for two conditions, with no-load and 30 kg compact-load at controlled laboratory condition 25°C and 50% relative humidity (RH). Compressive, shearing, torque, joint reaction force, and erector-spine forces for kinetic and angular changes of neck, trunk, thigh, forearm, upper arm, and leg were analysed by biomechanical analysis software (Ergomaster 4.6). A paired t-test and repeated measures analysis of variance were applied to determine the significant effects of the load on dependent variables. Results: Significant changes were found in kinetic (compressive, shearing, torque, joint reactive force, and erector spine force) and kinematic (neck and trunk) parameters with subsequent increments of loads. Conclusion: From this study, it was concluded that walking in uphill condition, compressive, shearing, torque, joint reactive force, and erector spine force was found to be increased by 2.58, 4.65, 4.06, 2.83, and 4.06 folds, the angular changes found in neck and trunk were 1.78 and 1.25 folds compared to no-load conditions, respectively. The exerted forces, namely compressive force 74.12%, shearing force 86%, joint reaction force almost 75%, and erector spine force 83.82%, were very close to the injury risk profile; only the change of torque was not much closer to the risk profile. Such findings could be used for recommending load carriage guidelines for future studies.

Experimental investigation of the external load effect on thermoelectric generator discharge time in a low power energy harvesting system

Thermoelectric generator systems are often evaluated and studied in open circuit and close circuit modes. In the open circuit case, minimum heat flux passes across the thermoelectric module and the module does not have any thermal losses. Moreover, in the close circuit system, the external consumer is connected to the module and higher heat is pumped from its hot side to cold side. Hence, investigating the effect of external load resistance as the consumer connected to the module on its response is a significant issue in thermoelectric systems. In this study, to evaluate the effect of various consumers (4, 8, 10, 15, 20 and 30 Ω) over the module on discharge time, output voltage and temperature on both sides of the module, thermoelectric systems lacking and containing phase change material as the useful means for energy storage and thermal management of thermoelectric system were designed and exposed to constant heat loads. Results of this study show that the power consumption of the internal resistance of the module (connected to the consumer) led to an increase in the temperature of both sides of the module compared to open circuit systems. Therefore, the thermal balance and temperature distribution over the module changes and more affected. The maximum output power and discharge time were obtained at the external resistance of 4 Ω (close to the average internal resistance of the module) in the studied systems. The phase change material prevented excessive temperature on the hot side during the charging process and provided proper thermal management to enhance voltage generation and discharge time. The thermoelectric generator is an effective technology in starting consumers with low resistance, such as light bulbs and remote controls.

BIFURCATION STATE AND RATIONAL DESIGN OF THREE-LAYER REINFORCED COMPOUND CONE-СYLINDER SHELL STRUCTURE UNDER COMBINED LOADING

An analytical-numerical approach to solving the problem of state bifurcation in terms of local and overall stability of a three-layer cone-cylinder shell structure discretely supported by intermediate rings, in particular of modern launch vehicles, under static combined loading by external pressure, axial forces, and torque is proposed in the paper taking into account the stiffness parameters of the intermediate rings in the plane of the initial curvature and for torsion. Corresponding solving equations for the problem are ordinary differential equations of the sixth order (for a cylindrical compart- ment with constant coefficients and for a conical one with variable coefficients along the axial coordinate). Differential relations that determine the conditions of conjugation through the intermediate ring are used. For the numerical solution, the finite difference method is used with central finite differences of the third and second order at the inner points of the shell determination segments and at its ends, respectively, and the second order differences with one step backward or forward at the conjugation points through the ring. The agreement of the calculation results with the known data for three-layer conical and cylindrical shells is shown, as well as in the limiting case, it is done when passing to a single-layer compound cone-cylinder structure. For the considered class of cone-cylinder shell structures, boundary surfaces are constructed that separate the stability region of the structure being under study, depending on the geometric and stiffness parameters of the compartments, reinforcing elements, and the external load condition. The external load effect on the parameter of the post-critical wave formation for the structure under investigation is studied, provid- ing the visualization of the deformation behavior. The analysis of the calculation results has shown that this approach to solving the problem of bifurcation and equistability of the compound structure compartments in relation to the local and overall forms of protrusion allows choosing rational geometric and stiff- ness parameters of the shell components and force elements in terms of improving the weight characteristics of the structure.

Long-term bolt preload relaxation and contact pressure distribution in clamping anchorages for CFRP plates

Clamping anchorages are commonly used to anchor carbon fiber reinforced polymer (CFRP) plates, and the anchoring performance is significantly impacted by bolt preload. This research presents experimental and numerical investigations of long-term bolt preload relaxation in clamping anchorages for CFRP plates. First, a compression test was conducted to obtain the elastic modulus in the thickness direction of CFRP plates. Subsequently, four types of relaxation tests (single bolt, planar and curved anchorage, external load effect, and thickened anchorage) were conducted, considering the effects of the number of CFRP plates, anchorage type, external load, and initial preload. The elastic interaction during the tightening process was also investigated. The contact pressure distribution was simulated through the finite element method, which is in good agreement with the experimental results obtained from pressure papers. To fit relaxation test results and predict million-hour relaxation, different theoretical models were employed. The results indicate that the number of CFRP plates is crucial to preload relaxation, and the presence of CFRP plates introduces strong elastic interactions between bolts in the anchorage. Preload relaxation also increases under external loads and with the increase in initial preload. Curved anchorage has less bolt preload relaxation in the long term under external loads. Additionally, thickened anchorages have a more uniform contact pressure distribution due to the improved pressure diffusion mechanism.

Modeling and Analysis of a Conical Bridge-Type Displacement Amplification Mechanism Using the Non-Uniform Rational B-Spline Curve.

This paper presents a new analytical model of a conical bridge-type displacement amplification mechanism (DAM) considering the effect of external loads and a piezostack actuator (PSA). With the merits of simple implementation and better fitting, the non-uniform rational B-spline (NURBS) is employed to parameterize conical connecting beams of the DAM, and an analytical model of the displacement amplification ratio and input stiffness is established based on Castigliano's second theorem. After that, considering the interactions with elastic loads and PSA, the actual displacement amplification ratio of the conical DAM is obtained, and the effect of the shape of connecting beams in the performance of the DAM is further analyzed. The proposed analytical model is verified by finite element analysis (FEA), and the results show a maximum error of 6.31% between the calculated value and FEA results, demonstrating the accuracy of the proposed model. A prototype of the conical DAM with optimized shape is fabricated and experimentally tested, which further validates the effectiveness and accuracy of the proposed analytical model. The proposed model offers a new method for analysis and shape optimization of the bridge-type DAM under specific elastic loads.

Crack propagation analysis of slewing bearings in wind turbines applying a modified sub-model technology

As slewing bearings in wind turbines are exposed to complex operational environments, they are prone to crack initiation, propagation and evolution that can lead to contact fatigue problems. Reliable crack extension prediction is a critical requirement. With the goal of obtaining more accurate crack characteristics, this study proposes a crack initiated contact finite element model (CI-CFEM) targeted at the raceway of slewing bearings by introducing a modified sub-model. In the application of the global finite element model (G-FEM) to the slewing bearing system, the rolling displacements of the ball and the boundary displacements are employed in CI-CFEM to take account of external ring deformations and the support conditions. The crack is embedded using FRANC3D, and the stress intensity factor distribution and propagation characteristics of the crack front are investigated. Furthermore, the effect of external load and the design parameters of the slewing bearing on crack propagation are explored, providing insight for optimizing the design of slewing bearings to extend service life. The results reveal that changing external loads and bearing parameters are an effective means of retarding crack propagation rate, while have relatively minor influence on crack growth angle.

Load transfer analysis of aircraft composite-metal hybrid joint fasteners under combined external loads and temperature

Due to the different thermal expansion coefficients of composite materials and metal materials, the variation of ambient temperature changes the load transfer ratio of composite-metal hybrid joint structures. In this paper, the Finite Element Method (FEM) is used to study the combined effects of external load and temperature field on the load distribution of CFRP-aluminium alloy single-lap hybrid joints. The effects of the temperature rise and fall on load transfer are considered. The simulation results show that the most dangerous position and the load transfer ratio of the hybrid show significant joint changes after the combination of the temperature effect under the external load.

Stress intensity factor and fatigue crack propagation assessment of mode-I failure in alumina-calcium hexaluminate refractories

Alumina-calcium hexaluminate refractories experience crack development under severe conditions, leading to a significant reduction in mechanical strength. The external finite element method and Paris' law were employed to investigate the effects of external load and in-situ crack length on stress intensity factor. Fatigue life and crack propagation process of refractories were simulated for varying CAx contents under Model I failure. The findings revealed a linear correlation between the stress intensity factor and external load for a fixed in-situ crack length (a≤16 mm). The ultimate strength of alumina-calcium hexaluminate refractories is inversely proportional to the in-situ crack length. The material's microstructure significantly influences the ultimate strength of refractories, whereas the crack propagation ratio at the interface-to-the aggregate level strongly affects fatigue life. Refractories with a CAx content of 29.78% exhibit the longest fatigue life, attributed to the favorable formation of CA6/CA2 and the highest interface-to-aggregate crack propagation ratio.

Analysis of an improved Nishihara creep model considering plastic strain accumulation

Rock-engineering structures, particularly subway excavation rock-engineering structures, are subjected to the long-term effects of external loading that may gradually damage and cause creep and severe plastic deformations or even progressive failure. The traditional Nishihara creep model cannot accurately describe the accelerated creep stage of rock with particularly obvious nonlinear characteristics. Based on this model, a damage variable that can consider the plastic strain accumulation is introduced in this study to replace the viscoplastic body in the traditional model with a damaged viscoplastic body and establish an improved Nishihara creep model. Using the superposition principle, the creep equations of the improved model in the one- and three-dimensional stress states are derived. The accuracy and rationality of the improved model are verified using uniaxial and conventional triaxial creep tests of mudstone and sandstone under different confining pressures. The improved model can not only accurately reflect the nonlinear characteristics of the creep curve in the decay and constant velocity stages but also describe the accelerated creep characteristics of mudstone and sandstone in a high-stress state. Its applicability and accuracy are superior to those of the traditional model. This study can provide a theoretical reference for subway tunnel excavation and stability analysis of deep roadway surrounding rocks.

Multi-physics simulation of mechano-electrochemical bidirectional coupling interaction of galvanic corrosion between Al alloy and 316L SS

Due to the limitations of experimental testing in material size and time scale, this work presents a mechano-electrochemical bidirectional coupling finite element method (FEM) simulation model on account of mechanistic and corrosion kinetics understanding in Al alloy-316L SS galvanic couple. The galvanic corrosion behavior and anodic dissolution deformation of the couple in 3.5 wt.% NaCl solution were analyzed. The effect of external load on galvanic corrosion initiation and propagation was investigated based on Gutman’s theory. The FEM model reveals that the galvanic corrosion is connected with the mechanical damage and the stress concentration coefficient, and highlights the crucial role of corrosion defect in the mechanical behavior of Al alloy. The results show that the external force aggravates the galvanic corrosion at the defects, deteriorating the protection of corrosion products. The thickness of the Al (OH)3 deposition layer reflects the electrochemical reactivity at different positions on the anode surface. The mechanical damage occurs initially at the corrosion defect and then extends to the middle of the anode. The stress concentration coefficient at the center of the anode gradually exceeds the position of the corrosion defect, resulting in mechanical failure at this position.

Fluid-structure interaction analysis of amniotic fluid with fetus and placenta inside uterus exposed to military blasts

Introduction: Pregnancy-related trauma is one of the leading causes of morbidity and mortality in pregnant women and fetuses. The fetal response to injury is largely dependent on the timing of fetal presentation and the underlying pathophysiology of the trauma. The optimal management of pregnant patients who have suffered an obstetric emergency depends on clinical assessment and understanding of the placental implantation process, which can be difficult to perform during an emergency. Understanding the mechanisms of traumatic injuries to the fetus is crucial for developing next-generation protective devices. Methods: This study aimed to investigate the effect of amniotic fluid on mine blast on the uterus, fetus, and placenta via computational analysis. Finite element models were developed to analyze the effects of explosion forces on the uterus, fetus, and placenta, based on cadaveric data obtained from the literature. This study uses computational fluid-structure interaction simulations to study the effect of external loading on the fetus submerged in amniotic fluid inside of the uterus. Results: Computational fluid-structure interaction simulations are used to study the effect of external loading on the fetus/placenta submerged in amniotic fluid inside the uterus. Cushioning function of the amniotic fluid on the fetus and placenta is demonstrated. The mechanism of traumatic injuries to the fetus/placenta is shown. Discussion: The intention of this research is to understand the cushioning function of the amniotic fluid on the fetus. Further, it is important to make use of this knowledge in order to ensure the safety of pregnant women and their fetuses.

Stress analysis of the contact problem in a functionally graded layer loaded with a distributed load and two rigid circular punches resting on an elastic two quarter planes

In this study, the solution of the contact problem in a functionally graded (FG) layer resting on elastic two quarter planes was done using the finite element method (FEM). The contact problem consists of two rigid circular punches loaded FG and two elastic quarter planes. P and Q loads are transmitted to the FG layer by two rigid circular punches. All surfaces in the problem were considered as frictionless and the weight effect is also taken into account. The two-dimensional model of the contact problem was created with the ANSYS package program based on FEM and the stress analyzes were performed. All operations of quarter planes and circular punches are done with standard ANSYS menus. However, defining the material properties of the FG layer and dividing into meshes in finite elements cannot be done with standard menus. For this reason, a special macro was added to the program in order to define the material properties of the FG layer and to perform the mesh division, and the necessary parameters were applied to the layer by this macro. In the study, the effects of external load, stiffness parameter (βh), density parameter (γh) and contact stresses of distributed load change, normal stresses, and stresses along the depth were investigated.

Effects of external loads on microstructure and properties of P92 steel

During the metal-solid phase transition, the mechanical properties of metal materials are affected by the nucleation rate and growth rate of grain. In this work, external loads (200 N, 400 N, 600 N, and 800 N) were applied to P92 steel during the heat treatment process in an attempt to improve and optimize the microstructure and mechanical properties of P92 steel. The effects of different external loads on the morphology, corrosion resistance, microhardness, and mechanical properties of P92 steel were investigated by using optical microscopy, microhardness testing, electrochemical testing, tensile strength measurements, and semi-automatic impact tester. The results show that the grain growth rate of P92 steel was moderate under an external load of 600 N; the grain distribution was uniform and orderly whereas the microhardness and corrosion resistance of the sample reached the optimum value (528 Hv). The tensile strength, yield strength, and elongation of the sample were 786 MPa, 525 MPa, and 37.8 %, respectively. However, the impact power of the P92 steel under an external load of 200 N was the minimum, and its average value was 132 J. The results depict that the external load can improve the mechanical properties of P92 steel.

Construction relationship between a functionally graded structure of bamboo and its strength and toughness: Underlying mechanisms

The special functional gradient structure of bamboo determines its excellent properties of strength and toughness, which make it an excellent candidate for biomimicking purposes in advanced material design. However, the construction relationship and underlying mechanism of the functionally graded structure in the direction of the bamboo wall and its excellent strength and toughness have not been elucidated. Accordingly, this study first conducts a quantitative analysis of the relationship between the directional gradient structure of the bamboo wall layer and its chemical composition and physical and mechanical properties. To this end, in situ scanning electron microscopy (in situ SEM) was used to investigate the mechanical behavior and failure mode of the bamboo wall layer under the effect of external loads, and to investigate the structure–activity relationship between the gradient structure of the bamboo wall layer and its strength and toughness, as well as the potential mechanism of action. From the perspective of structural mechanics, the mechanical model of the bamboo wall direction under the applied load was analyzed, and the mechanism by which the bamboo wall gradient structure improves the strength and toughness of bamboo was further elucidated. The results showed that the uniform gradient distribution of the vascular bundles and their interfaces in the direction of the bamboo wall determines the gradient distribution of its chemical components and physical and mechanical properties. Together, the uneven deformation of parenchyma cells and fibers, multi-path propagation of cracks, fiber bridging, pull-out and fracture constitute the mechanism by which the bamboo gradient structure contributes to its strength and toughness. This study provides a theoretical basis and innovative ideas for the design of biomimetic advanced materials based on the bamboo wall gradient structure by revealing the potential close relationship between the excellent mechanical properties of bamboo of high strength and toughness and its functional gradient structure.

엎드린 자세에서 엉덩관절 폄 동작 시 외적 부하가 복부 근육의 두께 변화에 미치는 영향

The purpose of this study was to study the effect of external loads on the thickness change of the transverse abdominis, intra oblique muscle, and extra oblique muscle when prone hip extension with knee flexion. This study was conducted on 25 healthy adults, and prone hip extension with knee flexion was performed with 0kg, 1kg, and 2kg of sandbags worn on the ankles in a prone position. The change in muscle thickness was measured using ultrasound equipment. The thickness of the transverse abdominis and internal oblique muscles increased significantly when prone hip extension was performed with an external load applied rather than prone hip extension without an external load. There was no significant change in muscle thickness of external oblique muscle. We propose that providing an external load when performing prone hip extension is more effective for activation of deep abdominal muscles.