External Loading Conditions Research Articles

Modeling of superelastic auxetic structures of Ti–Zr base alloy

The superelastic properties of a novel shape memory Ti–24Zr–10Nb–2Sn alloy were evaluated in two different auxetic geometrics embedded in an airfoil by the nonlinear finite element software Abaqus. In the first part, a constitutive model was developed to determine the phenomenology and mechanical response of shape memory alloy in a superelastic state. In the second part, a numerical model of re-entrant and chiral auxetic structures was developed. The beam modeling was selected due to its efficiency in contrast to the shell and 3D solid elements. The chiral structure (simple AAS and complex AAC) is accommodated within the airfoil providing flexibility and ability to withstand loads. A larger displacement with limited strain of the airfoil was observed in both conditions. Numerical results of auxetic structural elements were consistent with experimental results. This study explores the superelastic capability of novel shape memory alloys embedded with auxetic core lattice as an alternative for soft morphing airfoil. • Finite element modeling of auxetic structures were developed to simulate superelastic capacity of Ti–24Zr alloy. • Two-dimensional model of the Eppler 420 airfoil structure was developed and evaluated for external loading conditions. • A constitutive model was developed to determine the mechanical response of shape memory alloy in a superelastic state. • The maximum stress is proportional to the number of sub-cells in auxetic structures. • A larger displacement with limited strain of the airfoil was observed in simple AAS and complex AAC chiral structures.

METHODOLOGY AND RESULTS OF THE SERIES P-2 GLASS SLABS DURABILITY TEST

The paper presents the results of studies of glass plates of series P-2 for durability, which were made of float glass sheets, the methodology of experimental studies of glass plates for durability, as well as the design of the test facility. The analysis of literature sources on the subject made it possible to study the main factors of application of glass slabs as load-bearing structures. Glass is characterized by high strength, but glass structures are not widely used because of the possibility of their sudden brittle fracture and the lack of reliable calculation methods. The strength and reliability of glass structures depend on the type and strength of glass, manufacturing technology, the magnitude of external load and the duration of its action. Glass structures are characterized by the phenomenon of rheology and sudden brittle fracture, so the study of their durability, at different levels of external static load will ensure their reliable operation for the required time. Durability of a structure is the time from the beginning of static load action, which does not exceed the destructive load, with its further endurance until the destruction of the structure. For experimental studies of the durability of glass slabs, there was a need to create a research technique to ensure the stability of the external static load during the entire experiment with the possibility to record the growth of the deflection of the glass slab, the time and the nature of the failure up to the very moment of their sudden brittle failure. The paper describes the methodology and presents the initial results of the experimental study of glass beam slabs for durability. The slabs were hinged to two supports and operated as a single-span beam under a steady static load. Based on the experimental data obtained on the fracture of glass slabs during the action of a steady static load, we can try to predict their durability.

Earthquake resistant design of reinforced concrete retaining walls considering the project location change effect

In this paper, the design process of reinforced concrete retaining walls is investigated under the issue of “project location change effect” which becomes a significant requirement to assess the earthquake resistant design depending on the new Turkish Building Earthquake Code-2018 (TBEC-2018). Within this context, in the light of the related code, fourteen different districts which are located in the Anatolian Side of Istanbul Province (Turkey) have been taken into consideration, to search for also the effects of the supported earth fill depth, the unit weight and the shear strength angle of surrounding soil and the external loading conditions. In this way, it has been aimed to focus on the application details of the design code and reflect the outcomes of the analysis in terms of the changes that happened in wall dimensions depending on the locations of project. Besides, with this study, it is aimed to reveal that the definition of type sectional wall will not be possible with the new code. As the result, the influence rates of the investigated project variants have been explained considering site-specific retaining wall design in terms of integrated relations of the design parameters.

An new elastic\u2013plastic analytical solution of circular tunnel under non-axisymmetric conditions

The surrounding rock is in the initial stress state before the tunnel excavation, and it undergoes the stress redistribution to reach the secondary stress state after the tunnel excavation. The surrounding rock is not only the main load source but also is an important part of the load bearing structure. Once the stress of some zone in the surrounding rock exceeds the strength of the rock mass, the part surrounding rock will enter into a state of plasticity or failure. Analytical solution is the most powerful mean to analyze this kind of underground cavern engineering problems. However, the existing solutions can not directly or simultaneously obtain the secondary stress field and excavation disturbance displacement field that we are concerned about. The implicit approximate solution cannot be degenerated to an accurate axisymmetric expression for the most existing non-axisymmetric elastic–plastic solutions. Therefore, this paper derives the elastic solution of a circular tunnel under the condition of the non-axisymmetric external load with the radial and shear inner loads. On this basis, the new elastic–plastic solution and the plastic zone radius equation of the circular tunnel under the conditions of the non-axisymmetric external load with radial inner load are derived. It can directly obtain the secondary stress field and excavation disturbance displacement field, and can degenerate to an accurate axisymmetric expression. The distribution characteristics of the analytical solution are in good agreement with the numerical test results, indicating that the new solution can provide a relatively accurate theoretical basis for the analysis and research of tunnel engineering.

Study on Seismic Isolation of Long Span Double Deck Steel Truss Continuous Girder Bridge

In order to improve the seismic performance of long-span double deck steel truss continuous girder bridge, taking Dao Qing Chau Bridge in Fuzhou as an engineering background, the isolation scheme of friction pendulum bearing (FPB) and friction pendulum bearing combined with viscous dampers is applied to study seismic performance. A three-dimensional dynamic model of the bridge is established using SAP2000. Taking three artificial seismic waves as seismic excitation, the seismic response of the seismic structure is calculated by nonlinear time history integration, and is then compared with the seismic response of the seismic reduction and isolation structure. The results show that the friction pendulum bearing (FPB) scheme and combined seismic dissipation and isolation (CSDI) scheme show a good seismic dissipation and isolation effect and ensure the safety of the bridge structure. However, for whole-bridge isolation, friction pendulum bearing (FPB) will produce certain residual deformations and additional stress of the bearing under the conditions of temperature and external load. For the purpose of protecting the bearing, it is recommended to use the combined seismic dissipation and isolation (CSDI) scheme.

Dynamic fracture behaviors and fragment characteristics of pre-compressed flawed sandstones

Because of tectonic stress and dynamic disturbance, underground rock masses containing pre-existing flaws usually undergo complex loading conditions combining static pre-stress (SPS) and external dynamic loads. Comprehending the mechanical behaviors of flawed rocks under coupled static-dynamic loads is helpful to assess the stability of underground engineering. This study presented a series of coupled static-dynamic compression experiments on sandstone containing two non-coplanar flaws. The results indicated that the dynamic strength of the flawed sandstone increased first and then decreased with the increase in the SPS for a given dynamic strain rate (DSR), and the coupled strength of the flawed sandstone was less dependent on the DSR under the SPS of 60% of the uniaxial compressive strength than the other SPS values. Low SPS and DSR generally induced an asymmetrically X-shaped shear failure mode of the specimen, while this failure pattern could be observed in the tests with high SPS and DSR. Moreover, both a greater SPS and a higher DSR could lead to smaller location parameter values in the generalized extreme value fitting and a higher fractal dimension of the rock fragments, resulting in a more severe crushing destruction of the flawed sandstone. In addition, this study demonstrates that both the fracture process zones and the higher-order stress terms in the Williams series expansion, which are often neglected in traditional related studies, cannot be thoughtlessly ignored when analyzing the crack initiation, propagation, and coalescence of flawed rocks.

A New Two-Stage Degradation Model for the Preload of Linear Motion Ball Guide Considering Machining Errors

Abstract Preload, which is widely applied in linear motion ball guide (LMBG) to eliminate clearance and increase stiffness, gradually decreases owing to wear, resulting in the degradation of the load-bearing capability and dynamic response of LMBG. However, no solution can be found on the modeling of the preload degradation of LMBG considering raceway profile error, ball diameter error, etc. Therefore, this paper presented a new two-stage degradation model to predict the preload variation of LMBG with considering machining errors. The model was experimentally verified with the prediction accuracy much higher than the model considering no machining errors at either of the two wear stages, which demonstrates the effectiveness of considering machining errors. Additionally, the effects of waviness errors, external load, and feed speed on the preload degradation of LMBG were discussed. The simulation results indicate that the preload loss rate rises with the increase of waviness error, external load and feed speed. For obtaining a longer effective service life of LMBG, it is helpful to select appropriate external load and feed speed conditions and improve the processing technique as well as the machined surface quality.

Stress-dependent nonlinear magnetoelectric effect in press-fit composites: A numerical and experimental study

Magnetoelectric (ME) composites have posed an immense research interest over the past few decades. Their multifunctional capabilities enable a wide array of applications like field and pressure sensors, energy harvesters, gyrators, etc. The voltage developed under applied magnetic fields in these composites is governed strongly by the stress and magnetization state of the magnetostrictive phase, which needs to be characterized effectively. Towards this end, magnetostriction measurements are carried out under applied stresses in Nickel to understand its magnetomechanical response. A three-dimensional magnetostrictive constitutive model is used to predict the magnetostrictive behavior, which is later implemented in COMSOL Multiphysics® using the external material module. The FE solutions obtained are validated against analytical solutions. The model is subsequently used to obtain FE solutions for the magnetoelectric response of press-fit composites subjected to general magneto-thermo-mechanical loading. Experiments are performed on the press-fit composite to validate the voltage response predicted by the developed model, which shows a good agreement. The developed FE model is used to conduct a parametric study to quantify the effect of external loading conditions, the shape of inclusion, and the field orientation with an effort to optimize the ME response in press-fit ME composites.

An instrumented walker in three-dimensional gait analysis: Improving musculoskeletal estimates in the lower limb mobility impaired

BackgroundIn three-dimensional (3D) gait analysis of individuals requiring a walking frame (walker), acquisition of artefact-free motion and force data is challenging. Without inclusion of handle-reaction forces alongside ground reaction forces, external forces used in musculoskeletal modelling are incomplete. This may increase dynamic inconsistencies between the model and measured motions and forces, thus, uncertainties in estimates of musculoskeletal load. Research questionTo develop an instrumented walker and evaluate the effects of including handle-reaction forces on residual forces during musculoskeletal modelling. MethodsAn instrumented walker measuring handle-reaction forces synchronously with motion capture and ground reaction force data was developed. 3D gait analysis was conducted in ten elderly participants recovering from a proximal femur fracture and requiring a walker for ambulation. Joint kinetics and residual forces were calculated between two external load conditions: (1) external loads applied using only force platforms; or (2) external loads applied using force platforms and walker handle-reaction forces. ResultsIncluding handle-reaction forces reduced residual forces and improved estimates of musculoskeletal loads of the torso (P = <0.001). SignificanceA wide instrumented walker measuring handle-reaction forces allows for the gait analysis of individuals requiring a walker and improves reliability of musculoskeletal dynamics.

The interaction of hydrogen with retained austenite in automotive steel grades

This work investigates the effect of a constant load on hydrogen diffusion through transformation induced plasticity (TRIP)-assisted and quenching and partitioning (Q&P) steel containing metastable retained austenite by combining electrochemical hydrogen permeation and thermal desorption spectroscopy. Furthermore, a comparison is made with ferrite/martensite dual phase (DP) steel, which serves as a reference material not containing any retained austenite. Material samples are placed at different external loading conditions, ranging from 50% to 125% of the yield stress. The permeation transients indicate a different response between TRIP steel and Q&P steel. In the latter, hydrogen diffusion is delayed for all stressed conditions, even at stresses in the elastic regime, whereas TRIP steels follows the same behaviour as the reference DP steel with increased hydrogen diffusivity in the elastic regime and decreased in the plastic regime.From subsequent thermal desorption spectroscopy performed on the specimens after the permeation test, the hydrogen desorption spectra of Q&P steel samples show a high temperature peak which is not present in the spectrum of the unloaded sample. Thus indicating that the retained austenite is capable of trapping hydrogen in a loaded condition. Due to the difference in matrix surrounding the austenite phase, it is reasoned that the discrepancy in trapping behaviour is due to the internal stresses present in the austenite in Q&P steel and the higher hardness of the surrounding matrix compared to TRIP steel.

Fatigue life analysis of aero-engine blades for abrasive belt grinding considering residual stress

Abrasive belt grinding technology is widely used in the processing of aero-engine blades. Residual stress is used as an indicator of grinding gauge integrity, which has a significant impact on the fatigue performance of aero-engine blades. In fatigue life research, experiments are mainly used to explore the influence of residual stress on fatigue life. Restricted by factors such as experimental efficiency and cost, it is necessary to simulate the influence of residual stress in the process of fatigue failure. Based on the theory of crack initiation and propagation, this paper proposes a life prediction algorithm considering residual stress; carries out a bending vibration fatigue experiment and simulation fatigue life analysis of aero-engine blade grinding with abrasive belt; compares the results of experiments and simulations and proposes a residual stress equivalent calibration method. Used theory, simulation, and experiment to verify the effectiveness of the method, and uses this equivalent calibration method to analyze the effect of residual stress on the fatigue life of aero-engine blades ground by abrasive belts. The experimental results show that the surface residual compressive stress will optimize the size and distribution of the surface stress during the service process of the aero-engine blade. Under the same external load and surface roughness conditions, a larger surface residual compressive stress will increase the aero-engine blade stiffness, reduce the aero-engine blade’s vibration amplitude, and reduce Surface stress, which in turn, has a beneficial effect on fatigue life. The proposed calibration method considering residual stress can accurately predict the fatigue life of aero-engine blades with a prediction accuracy up to 90%.

Unified fatigue life prediction of bolts with different sizes and lengths under various axial loading conditions

Bolts tend to show different fatigue behavior with respect to the size or shape of a bolt and the level of preload though it is the same material. This makes it difficult to predict the fatigue life of bolts. In this study, a novel method to construct a unified stress-life (S-N) curve was proposed for the three different bolts with different sizes and lengths subjected to various external axial loading conditions and preloads, ranging from 44 % to 88% of the ultimate tensile stress. A total of 133 experiments for 46 different fatigue conditions were conducted and finite element analysis was also performed to calculate multiaxial stress components at the root of the thread. The fatigue characteristics of the bolts were investigated depending on various loading conditions, and the life prediction performance with fitted S-N curves was compared with respect to four mean stress correction models. The unified S-N curve showed high accuracy in life prediction; 15 % mean absolute error without exceeding ± 50 % for finite life loading conditions.

Musculoskeletal modelling based estimates of load dependent relative muscular effort during resistance training exercises

ABSTRACT The purpose of this study was to investigate the relative muscular effort (RME) of the hip and knee extensor and ankle plantarflexor muscle groups during the back squat (BS) and split squat (SS) exercises across four external load conditions. Motion capture and force plate data were collected as participants performed the BS and SS at 0%, 25%, 50%, and 75% of their body-mass. These data were used to calculate net joint moments (NJM) at the hip, knee, and ankle of the front leg during the SS and the matched leg during the BS. A musculoskeletal model, which accounted for force-length-velocity properties of 52 muscles, was used to estimate the maximal possible NJM (NJMmax) of the hip and knee extensor and ankle plantarflexor muscle groups. RME was calculated as the ratio between NJM and NJMmax, and compared across exercises and loads. The results indicated that while hip extensor RME increased across all loads, the increases in hip extensor RME were disproportionately greater during the SS at loads of 50% and 75%. Knee extensor RME increased linearly across loads and did not differ between exercises. These results provide coaches and athletes with detailed information about how to optimise resistance training specificity.

Fracture properties of the gold mine tailings-based geopolymer under mode I loading condition through semi-circular bend tests with digital image correlation

Sustainably reusing mine tailings and reducing the economic costs of storing them is an ongoing concern in the geomechanics field. This paper discusses the process of utilizing MTs in the manufacture of geopolymer through alkaline activation. Since geopolymer is subjected to various external and internal loading conditions that could result in failures and fractures, understanding the fracture behaviors of MTs-based geopolymer is critically important for its use and application. The fracture behaviors of geopolymer remain largely unexplored. The study presented in this paper addressed this knowledge gap by evaluating the mode I fracture tests that are commonly used in the rock mechanics field for adoption to test geopolymer by using three-point bending instrument and considering various influential parameters, such as notch depths. The geopolymer specimens in this study were cast into cylindrical molds by mixing different mine tailings with a 10 M NaOH solution at a water/tailings ratio of 22% and then cured with a slightly elevated temperature of 72 ± 2℃, for seven days. Thereafter, the cylindrical specimens were cut into semi-circular specimens and a series of semi-circular bending tests were performed. The mode I fracture toughness, KIC, of the geopolymer were estimated and the sensitivity of the notch depth was evaluated based on linear elastic fracture mechanics for the specimens with current sizes. Also, the strain behaviors of the semi-circular specimens were investigated through digital image correlation mapping. The mode I fracture behaviors were studied and the force-displacement behaviors of the semi-circular bending specimens with regard to the notch depths were compared and interpreted. Further, the strain properties of the semi-circular bending specimen were evaluated with respect to different load levels and the fracture process zone and crack tip opening displacement of the geopolymer then were measured by digital image correlation analyses.

Current Trends in Integration of Nondestructive Testing Methods for Engineered Materials Testing.

Material failure may occur in a variety of situations dependent on stress conditions, temperature, and internal or external load conditions. Many of the latest engineered materials combine several material types i.e., metals, carbon, glass, resins, adhesives, heterogeneous and nanomaterials (organic/inorganic) to produce multilayered, multifaceted structures that may fail in ductile, brittle, or both cases. Mechanical testing is a standard and basic component of any design and fabricating process. Mechanical testing also plays a vital role in maintaining cost-effectiveness in innovative advancement and predominance. Destructive tests include tensile testing, chemical analysis, hardness testing, fatigue testing, creep testing, shear testing, impact testing, stress rapture testing, fastener testing, residual stress measurement, and XRD. These tests can damage the molecular arrangement and even the microstructure of engineered materials. Nondestructive testing methods evaluate component/material/object quality without damaging the sample integrity. This review outlines advanced nondestructive techniques and explains predominantly used nondestructive techniques with respect to their applications, limitations, and advantages. The literature was further analyzed regarding experimental developments, data acquisition systems, and technologically upgraded accessory components. Additionally, the various combinations of methods applied for several types of material defects are reported. The ultimate goal of this review paper is to explain advanced nondestructive testing (NDT) techniques/tests, which are comprised of notable research work reporting evolved affordable systems with fast, precise, and repeatable systems with high accuracy for both experimental and data acquisition techniques. Furthermore, these advanced NDT approaches were assessed for their potential implementation at the industrial level for faster, more accurate, and secure operations.

Numerical Nonlinear Static Analysis of Cutout-Borne Multilayered Structures and Experimental Validation

The influence of two different types of nonlinear strain-displacement kinematics (Green–Lagrange and von Kármán) and their importance are investigated in this analysis by computing the static deflection and stress (normal and shear) values of cutout abided composite structures. The structural deformation behavior under the external loading conditions is derived with a higher-order polynomial without hampering the strain and stress (in-plane and out-of-plane) continuity. The mathematical formulation of the curved structure is derived, and the governing equation order is reduced using nonlinear finite element steps. A generic computer code is prepared using the derived mathematical formulation in conjunction with the isoparametric finite element technique in a MATLAB environment. The final output (that is, the nonlinear deflection and stress data) is predicted using a robust nonlinear solution method (Picard’s iteration). The suitability of full-scale geometrical nonlinearity (Green–Lagrange strain) in the framework of a higher-order displacement field model for the laminated structure is established by comparing the experimental deflection data and published analytical solutions. Furthermore, a series of numerical examples is solved to show the influences of different individual and/or the combined parametric influences on the structural deflections and the normal/shear stress (in-plane and out-of-plane) values, including the variable geometrical shapes.

Nonlinear Vibration Characteristics of the Involute Spline Coupling in Aeroengine with the Parallel Misalignment

In order to control the vibration of the involute spline coupling in aeroengine well and reduce the fretting wear, a bending–torsion coupling nonlinear vibration model of the involute spline coupling with the misalignment was proposed, and a dynamic meshing stiffness function with multiteeth engagement was established. Then, the influence of different misalignment, wear, and rotation speeds with different misalignment on the nonlinear vibration characteristics of the involute aviation spline coupling was explored. The result shows that with an increase of the parallel misalignment, the system experienced the state of a single period, a quasiperiod, multiperiod, and chaos but finally only alternated between the quasiperiod and the chaos state. The uneven wear of each tooth of the spline displayed a significant influence on the vibration of the spline coupling, and the influence of the uniform wear was smaller under given conditions here. Furthermore, with an increase of the speed, the larger the misalignment was, the more times the system entered or left the chaos state were. The model proposed here is found to be closer to the actual working conditions, and the analysis results can provide more accurate external load conditions for the prediction of the fretting damage of the spline coupling in aeroengine.

Optimization-based subject-specific planar human vertical jumping prediction: Effect of elbow flexion and weighted vest.

Jumping strategies differ considerably depending on athletes' physical activity demands. In general, the jumping motion is desired to have excellent performance and low injury risk. Both of these outcomes can be achieved by modifying athletes' jumping and landing mechanics. This paper presents a consecutive study on the optimization-based subject-specific planar human vertical jumping to test different loading conditions (weighted vest) during jumping with or without elbow flexion during the arm-swing based on the validated prediction model in the first part of this study. The sagittal plane skeletal model simulates the weighting, unweighting, breaking, propulsion phases and considers four loading conditions: 0%, 5%, 10%, and 15% body weight. Results show that the maximum ground reaction forces, the body center of mass position, and velocities at the take-off instant are different for different loading conditions and with/without elbow flexion. The optimization formulation is solved using MATLAB® with 35 design variables with 197 nonlinear constraints for a five-segment body model and 42 design variables with 227 nonlinear constraints for a six-segment body model. Both models are computationally efficient, and they can predict ground reaction forces, the body center of mass position, and velocity. This work is novel in the sense that presents a simulation model capable of considering different external loading conditions and the effect of elbow flexion during arm swing.

Analysis of planes within reduced micromorphic model

A plane within reduced micromorphic model subjected to external static load is studied using the finite element method. The reduced micromorphic model is a generalized continuum theory which can be used to capture the interaction of the microstructure. In this approach, the microstructure is homogenized and replaced by a reduced micromorphic material model. Then, avoiding the complexity of the microstructure, the reduced micromorphic model is analyzed to reveal the interaction of the microstructure and the external loading. In this study, the three-dimensional formulation of the reduced micromorphic model is dimensionally reduced to address a plane under in-plane external load. The governing system of partial differential equations with corresponding consistent boundary conditions are discretized and solved using the finite element method. The classical and nonclassical deformation measures are then demonstrated and discussed for the first time for a material employing the reduced micromorphic model.

Crack layer model for semi-elliptical surface cracks in HDPE pipes and application in buried pipes with complicated loading conditions

The crack layer (CL) model can be used to theoretically simulate unique discontinuous slow crack growth (SCG) and the consequent lifetime of pipe-grade high-density polyethylene (HDPE). However, its application has been limited to several specimen configurations and 1-dimensional (1D) crack growth in pipes. In this study, a 2-dimensional (2D) CL growth model was formulated for a semi-elliptical surface crack in an HDPE pipe, for the first time. The 2D semi-elliptical discontinuous SCG kinetics of the inner surface of the pipe were successfully simulated. In addition, the proposed model was applied to a buried HDPE pipe under the complicated loading condition, e.g., internal pressure, ground pressure induced by structures and traffic loads, as well as the point load due to stones contacting the pipe surface. As the point load exerted by such hard objects within the soil medium can reduce the structural integrity of the buried pipes, this effect is a valid consideration. Various levels of these loading conditions were applied for semi-elliptical CL growth simulations, with different stone sizes in contact with the buried pipe. The results indicate that the diameter of the stone influences semi-elliptical crack propagation behavior and significantly reduces failure time even under the same external loading condition. In addition, it was observed that the lifetime reduction rate depends on the ratio of the internal pressure to ground pressure. This study broadens the applicability of the 2D CL model for buried HDPE pipes to more practical situations and quantifies the effect of stone-embedded soils on SCG kinetics and its lifetime.