Maximum Allowable Strain Research Articles

Seismic Performance Assessment for Serviceability of Geosynthetic Reinforced Embankments

Embankments in the field of civil engineering were historically not given much attention in terms of their ability to withstand seismic activity, as they were considered to be non-critical structures. However, in recent years, the seismic stability of embankments has gained increasing importance in the field of geotechnical engineering. This increased significance is due to the need to quickly restore functional infrastructure after earthquakes. The occurrence of lateral spreading, resulting from foundation liquefaction, is the primary factor leading to embankment distress in geotechnical engineering during seismic events. To address this issue, this study presents a novel approach that employs geosynthetic basal reinforcement. The research paper presents a technique that uses geosynthetic basal reinforcement to manage the lateral spreading of embankments both pre- and post-earthquakes, guaranteeing their ongoing effectiveness. The proposed approach utilizes a pseudo-static limit equilibrium method for determining the tensile load produced in the basal reinforcement. The serviceability criteria establish the maximum strain permitted in the basal reinforcement by imposing a restriction on the horizontal movement of the embankment toe. By taking into account the tensile load of the reinforcement and the maximum allowable strain, it is feasible to establish an appropriate geosynthetic reinforcement that considers various factors including tensile strength, strain, design life, installation, and durability impacts.

Blade Structure Analysis of 2 MW V-Shaped Vertical Axis Wind Turbine Using Numerical Simulation

The intensive research on large-scale Vertical Axis Wind Turbine (VAWT) couldprovide an alternative to Horizontal Axis Wind Turbine (HAWT) in offshore deployment for the future. Regarding this fact, this article develops a conceptual design of the VAWT blade structure and analyzes its feasibility using numerical simulation. The blade structure is designed for 2 MW Darrieus type V- shaped VAWT. The blade is tapered, 90m long, and inclined at 35° to the vertical axis. Initially, the blade design is tested for ultimate strength test according to IEC 61400-01 standard using aluminum alloy and homogenized composite material. In doing so, maximum aerodynamic loading on the blade is calculated after steady state 3-D RANS CFD simulation of the blade in ANSYS Fluent. The Finite Element Method (FEM) model of the blade is created using shell element in ANSYS Static Structural with structured meshing strategy, and tested with the aerodynamic load using the one-way Fluid-Structure Interaction (FSI) technique, to obtain mesh independent solution. The impact of the using 2, 3, and 4 number of shear webs is then analyzed on the selected mesh model of the blade. Finally, a four-shear web model of the blade is tested under extreme conditions. The thickness of the blade surface and shear web are varied to test maximum deflection at the tip, and maximum allowable strain of the blade. After obtaining the required blade structure, the deformation, maximum equivalent stress, and maximum equivalent strain for the blade are studied at rotation Tip Speed Ratio (TSR) of 5 under aerodynamic and gravitational loading, using both materials. The study showed significant deflection at the tip of the blade for the tower-less V-VAWT blade, suggesting an alternative support mechanism for the blade. Also, the study concluded that better structural robustness is achieved while using a composite material instead of an aluminum alloy. This article provides basis to study structural behavior of the novel V-VAWT blades and contribute to continuing research on obtaining optimized blade structure for such turbine.

Mechano-Graded Electrodes Mitigate the Mismatch between Mechanical Reliability and Energy Density for Foldable Lithium-Ion Batteries.

Flexible lithium-ion batteries (LIBs) with high energy density are highly desirable for wearable electronics. However, difficult to achieve excellent flexibility and high energy density simultaneously via the current approaches for designing flexible LIBs. To mitigate the mismatch, mechano-graded electrodes with gradient-distributed maximum allowable strain are proposed to endow high-loading-mass slurry-coating electrodes with brilliant intrinsic flexibility without sacrificing energy density. As a proof-of-concept, the up-graded LiNi1/3 Mn1/3 Co1/3 O2 cathodes (≈15mg cm-2 , ≈70µm) and graphite anodes (≈8mg cm-2 , ≈105µm) can tolerate an extremely low bending radius of 400 and 600µm, respectively. Finite element analysis (FEA) reveals that, compared with conventionally homogeneous electrodes, the flexibility of the up-graded electrodes is enhanced by specifically strengthening the upper layer and avoiding crack initiation. Benefiting from this, the foldable pouch cell (required bending radius of ≈600µm) successfully realizes a remarkable figure of merit (FOM, energy density vs bending radius) of 121.3 mWh cm-3 . Moreover, the up-graded-electrodes-based pouch cells can deliver a stable power supply, even under various deformation modes, such as twisting, folding, and knotting. This work proposes new insights for harmonizing the mechanics and electrochemistry of energy storage devices to achieve high energy density under flexible extremes.

Non-linear analysis of orthotropic hyperelastic plate using VAM

An asymptotically accurate zeroth-order constitutive relation between 2D strains and stress tensor for an orthotropic hyperelastic material is derived using the Variational Asymptotic Method (VAM). Material nonlinearity is encompassed through the hyperelastic material model while geometric nonlinearity is by allowing finite displacements and rotations. Moderate strains of order 20% are considered. The small parameters such as the ratio of thickness to characteristic dimension, and maximum allowable strain (0.2) separate strain energy density into different orders. The analysis starts with the 3D strain energy density function and is divided into the thickness analysis (1D) and mid-surface analysis (2D). The 1D analysis leads to analytical expressions for warping functions, constitutive relations, and recovery relations. The 2D analysis is based on a non-linear finite element method that takes the constitutive relation as its input and obtains 2D displacements. The recovery relation converts them to 3D field variables i.e. displacements, strains, and stresses. The theory is applied to a square clamped plate subjected to uniformly distributed pressure. The results are accurate and obtained in a computationally efficient manner.

Performance of high-damping rubber bearings for seismic isolation of residential buildings in Turkey

The applicability of high-damping rubber bearings for seismic isolation of residential buildings in Turkey is studied using numerical and experimental approaches. Seismic isolation system composed of high-damping rubber bearings is designed according to the recently updated Turkish Building Seismic Code-2018 (TBSC2018). Three model buildings of different height at assumed seismically active area are chosen from an actual building database, on which, equivalent lateral force procedure, and time history analyses are carried out.The seismic responses of the buildings are evaluated and the seismic isolation system's efficiency is confirmed. It is pointed out that the requirements in the new code in terms of the maximum allowable shear strain of elastomeric isolators are excessively conservative for those isolators with much larger capacity which is verified by sufficient test data, and as a result, designed isolator size becomes larger than necessary from a practical aspect. In order to verify the isolator design without compliance of shear strain limitation in the code, full-scale prototypes of high-damping rubber bearings are specially designed, developed and are subjected to dynamic loading test under test protocol specified in the code. The specific values of test conditions, such as compressive force, shear displacement and frequency, are developed referring several projects in Turkey. The results are comprehensively discussed and the applicability of high-damping rubber bearing for seismic isolation of residential buildings in Turkey is concluded with numerical and experimental approaches and a possible modification of TBSC2018 regarding maximum shear strain is proposed.

Effects of environmental conditions on the axial tension–compression fatigue behavior of carbon/epoxy plain-weave laminates containing flaws

The objective of this work is to investigate the effects of environmental conditions on the axial fatigue behavior of a carbon/epoxy plain-weave laminate with an embedded flaw subjected to a partially reversed cyclic load (stress ratio R = −0.1) in tension–compression. This specific material is more commonly used in aerospace engineering for the manufacturing of aircraft structural parts, which are directly exposed to various environmental conditions during service. Specific environmental and loading conditions that are appropriate to simulate real-life conditions are considered to observe and collect information about the material's behavior. For the investigation, dry and wet coupons were submitted to room temperature, 82 and 121 ℃ under loading frequencies of 7 and 15 Hz. A maximum allowable strain increase criterion is used to monitor the flaw growth threshold or delamination onset, during fatigue testing. The ultrasonic imaging (C-scan) technique is used to verify and confirm the delamination onset. Results show that the delamination onset strain increase criterion, along with fatigue life, generally decreased as the operating temperature and humidity were increased and that frequency had little effect on the delamination onset fatigue life. The S– N curves obtained from the tension–compression fatigue data were then compared to those of a previous work carried out in tension–tension fatigue loading. Results show a clear degradation in the delamination onset fatigue life of the coupons tested under tension–tension cyclic loading when the minimum tensile component of the cyclic load was replaced with a compressive load of the same magnitude.

A general global-local modelling framework for the deterministic optimisation of composite structures

This work deals with the multi-scale optimisation of composite structures by adopting a general global-local (GL) modelling strategy to assess the structure responses at different scales. The GL modelling approach is integrated into the multi-scale two-level optimisation strategy (MS2LOS) for composite structures. The resulting design strategy is, thus, called GL-MS2LOS and aims at proposing a very general formulation of the design problem, without introducing simplifying hypotheses on the laminate stack and by considering, as design variables, the full set of geometric and mechanical parameters defining the behaviour of the composite structure at each pertinent scale. By employing a GL modelling approach, most of the limitations of well-established design strategies, based on analytical or semi-empirical models, are overcome. The GL-MS2LOS makes use of the polar formalism to describe the anisotropy of the composite at the macroscopic scale (where it is modelled as an equivalent homogeneous anisotropic plate). In this work, deterministic algorithms are exploited during the solution search phase. The challenge, when dealing with such a design problem, is to develop a suitable formulation and dedicated operators, to link global and local models physical responses and their gradients. Closed-form expressions of structural responses gradients are rigorously derived by taking into account for the coupling effects when passing from global to local models. The effectiveness of the GL-MS2LOS is proven on a meaningful benchmark: the least-weight design of a cantilever wing subject to different design requirements. Constraints include maximum allowable displacements, maximum allowable strains, blending, manufacturability requirements and buckling factor.

Experimental investigation on response characteristics of buried pipelines under surface explosion load

In order to study the impact of surface explosion load such as terrorist attacks and disasters on buried pipelines, the field experimental study of the dynamic response characteristics of buried pipelines under surface explosion load was carried out by means of explosion experiment of on-site pre-buried pipelines and explosives, combined with blasting vibration and dynamic strain monitoring. The attenuation law of the ground surface peak particle velocity (PPV) above the pipeline was analyzed under explosion load with varied explosive charge and different blasting distances, meanwhile, the PPV and the peak particle strain (PPS) distribution characteristics of buried pipelines under surface explosion load are studied. The function expression of the relationship between ground surface's PPV, pipeline's PPV and pipeline's PPS is established on the basis of field experiment results. Integrated with the maximum allowable strain theory of pipelines, the safety evaluation of buried pipelines under blasting load is carried out. Then, the “safety area” of explosion parameters for preventing pipeline damage is proposed.

Influence of cold rolling deformation mechanisms on the grain refinement of Fe–15Mn–10Cr–8Ni–4Si austenitic alloy

The efficiency of rolling deformation mechanisms on grain refinement during recrystallization annealing was studied in Fe–15Mn–10Cr–8Ni–4Si austenitic alloy samples rolled to different strains at 0, 25, 100 and 200 °C. Two deformation routes were examined: rolling to a fixed strain (r) of 48% and rolling to strains of 55, 67, 88 and 93%, which were identified as the maximum allowable strains achieved in the alloy at 0, 25, 100 and 200 °C, respectively. The increase in rolling temperature changed the major deformation mechanism from deformation-induced ε-martensitic transformation (ε-MT) at 0 < T ≤ 25 °C, which provided the formation of multi-phase austenite/ε-martensite microstructure, to mechanical twinning of austenite at 100 < T < 200 °C; both of these deformation mechanisms were accompanied by dislocation slip. Moderate rolling strains of 48–67% were sufficient to produce multi-phase microstructures with a sufficiently high driving force for the formation of truly recrystallized grains (approximately 2 μm in size) during annealing at 700 °C for 30 min. The change in the deformation mechanism from deformation-induced ε-MT to mechanical twinning reduced the recrystallization driving force due to a decrease in stored dislocation density and an increase in microstructure homogeneity. In a single-phase microstructure, rolling strains above 88% were required to provide a sufficiently large driving force for the formation of fully recrystallized fine-grained microstructures during annealing.

Finite element method-based modeling of bending under tension friction test of deep drawing quality steel sheets

Understanding of the effect of the friction on the sheet deformation is a key factor in design and realization of stamping process. Among others, bending under tension friction test simulates the frictional phenomena on rounded edge of punch in sheet metal forming operations. In this paper, change of friction coefficient with 1-mm-thick deep drawing quality steel sheet deformation was evaluated using a special tribological simulator which simulates the friction in rounded edge of punch. The results of experimental investigations have been used to verify the results of numerical modeling carried out inmSC. Marc 2014 program. The friction coefficient value and contact stresses have been determined numerically. The results show that the distribution of the normal and friction stresses is very non-uniform along the wrap angle of the cylindrical countersample and along the specimen width. It has been concluded that FEM-based investigations allow a fast and suitable selection of the punch edge profile ensuring an increase of maximum allowable sheet strains.

Experimental and modelling study on nonlinear time-dependent behaviour of thin spray-on liner

Thin spray-on liners (TSLs) are fast-setting multi component polymeric materials applied on rock or coal surface with a thickness of 2–5 mm that have fairly high tensile strength, adhesion, and elongation capabilities. Compared to conventional surface support elements, TSLs with polymer content exhibit different material responses over time. As a matter of fact, the creep behaviour of TSLs under a constant load has a significance for the evaluation of the long term performances of TSLs. This paper investigates the nonlinear creep behavior of a polymer based TSL for different curing times. Experimental studies were completed to show the nonlinear time-dependent response of the liner under various constant load and curing time conditions. Dogbone shape test specimens were sustained under constant loads up to 2 months of testing time for different test sets. New equations were proposed for rupture time prediction (creep rupture envelopes) which may aid support design engineers to estimate the effective permanent support time and maximum allowable strain amount of the TSL. Test results were used to construct nonlinear viscoplastic models and viscoelastic models consisting of one independent spring and multi Kelvin–Voight elements. A good agreement was obtained between model predictions and experimental values. Generated constitutive models might aid to further numerical studies in TSL literature.

Impact of homogenization heat treatment on the high temperature deformation behavior of cast AZ31B magnesium alloy

Uniaxial isothermal compression tests were conducted on cylindrical specimens extracted from a DC cast AZ31B ingot with and without a homogenization treatment in the temperature range of 300°C–500°C, at strain rates of 10−3s−1–1.0s−1. As-cast specimens (without a homogenization treatment) exhibited cracking at a strain rate of 1.0s−1 for deformation temperatures of 400°C and above. The cracking is believed to be associated with incipient melting of the γ-Mg17Al12 phase. Homogenization of the specimens at 450°C for 5h improved the hot workability and no cracking was observed under the investigated conditions. Deformation of the cast-homogenized material was successfully conducted at 500°C and 1.0s−1, to a final strain of 1.0. The volume fraction of dynamically recrystallized (DRX) grains was observed to increase with strain, but the DRX grain size exhibited little to no change. The DRX grain size however did increase with deformation temperature and with decreasing strain rate. Increasing the deformation temperature from 350°C to 500°C increased the maximum allowable strain before cracks were observed at the surface. Additional specimens were homogenized at temperatures of 400°C or 500°C, for times of 3h or 5h, followed by a water quench or air cooling. Under all circumstances, incipient melting of the γ-Mg17Al12 phase was no longer observed upon heating using differential scanning calorimetry (DSC). Furthermore, homogenization at a temperature of 350°C for up to 8h resulted in partial dissolution of the γ-Mg17Al12 phase, and an increase in incipient melting onset temperature was observed by DSC.

Development of a strain dependent pressure law for superplastic forming of 2024 aluminium alloy

AbstractSuperplastic forming is widely used in aeronautic industry to produce complex parts due to the ability of the material to sustain very large deformation. One of the main problems lies in the determination of the pressure law applied during the process to control the strain rate evolution. Many algorithms exist in numerical codes to predict the pressure law, but they generally use a constant value of maximum strain rate as reference to control the pressure law. These simulations give globally good results while lead to long cycle times. In this work, the pressure law is computed in order to control the forming process by a non‐constant strain rate. The value of the optimum strain rate is indeed adapted to the level of strain developed within the part during the forming. This approach is applied on the 2024 aluminium alloy. Uniaxial tensile tests are performed to determine the influence of strain level on the maximum allowable strain rate. Then, the new pressure control algorithm is implemented in the ABAQUS code. Numerical simulations of generic parts are finally performed and the results show a significant reduction of the forming time without decreasing the quality of the parts.

Development of a finite element model for comparing metal and composite fuselage section drop testing

ABSTRACTPart of the work of AircraftFire, a project investigating the effects of fire and crash on aircraft survivability, is presented. This work compares the effect of changing the material model from metallic to composite on the impact damage and floor acceleration characteristics. First, the metallic two- and six-frame sections of an A320 are analysed, with drop test data to compare for reference and validation. The six-frame metallic and composite sections for a larger, A350-like aircraft are examined to compare the relative safety of newer composite fuselages. The composite model includes both a quasi-isotropic analysis with damage based on maximum allowable strain, and a ply-by-ply laminate model with Hashin damage. Energy dissipation and acceleration analyses follow, which show the potentially dangerous acceleration pulses for passengers seated in the cabin.

Design, Implementation and Analysis of 3D Printed Grasshopper Robot for Jumping Mechanism

This scientific paper consists of the analysis of the grasshopper jumping mechanism through literature studies, manufacturing, analysis and experimentation to enhance the knowledge to the manufacturing and analyzing of the artificially developed grasshopper-like robots. The first step involved the understanding of the actual grasshopper mechanisms which was carried out by the dissection of actual grasshopper bodies to analyze the hind leg movements, actuating muscles and structured sizes of the involved organs. The next step involved the development structural of the prototype consisted of design of the grasshopper jumping robot and the durability of the structure was checked at the critical locations. The results indicated that the strains produced in the tibia (immediately before and immediately after the jump) and femur of the designed structure was 2.5.10-5, 3.2.10-5 and 634.10-5 respectively. Whereas, the maximum allowable strain of the material during elastic deformation is 660.10-5, so the design of the structure could satisfy the strength requirements. The structural strength of the tibia and femur with the vertical printing were also in line with the stress requirements. Fabrication and jumping test was carried out which indicated 5 times higher jumps for the designed and fabricated grasshopper like jumping robot. This result is very helpful in robotic industry for the smooth movements of the robots for carrying out the intended function on rough terrains.

Three-dimensional invariant-based failure criteria for fibre-reinforced composites

A new three-dimensional failure criteria for fibre-reinforced composite materials based on structural tensors is presented. The transverse and the longitudinal failure mechanisms are formulated considering different criteria: for the transverse failure mechanisms, the proposed three-dimensional invariant-based criterion is formulated directly from invariant theory. Regarding the criteria for longitudinal failure, tensile fracture in the fibre direction is predicted using a noninteracting maximum allowable strain criterion. Longitudinal compressive failure is predicted using a three-dimensional kinking model based on the invariant failure criteria formulated for transverse fracture. The proposed kinking model is able to account for the nonlinear shear response typically observed in fibre-reinforced polymers. For validation, the failure envelopes for several fibre-reinforced polymers under different stress states are generated and compared with the test data available in the literature. For more complex three-dimensional stress states, where the test data available shows large scatter or is not available at all, a computational micro-mechanics framework is used to validate the failure criteria. It is observed that, in the case of the IM7/8552 carbon fibre-reinforced polymer, the effect of the nonlinear shear behaviour in the failure loci is negligible. In general, the failure predictions were in good agreement with previous three-dimensional failure criteria and experimental data. The computational micro-mechanics framework is shown to be a very useful tool to validate failure criteria under complex three-dimensional stress states.

New method to determine proper strain rate for constant rate-of-strain consolidation tests

The development of a new semiempirical method to predict the proper strain rate for constant rate-of-strain (CRS) consolidation tests is described herein. The validity of the proposed method is analyzed using experimental results from CRS and incremental loading tests on four types of soil: Lake Bonneville clay, Massena clay, kaolinite, and montmorillonite. It is found that the maximum allowable strain rate depends on the initial void ratio of the soil and thus is related to the compressibility of the soil. The effect of the strain rate on the distribution of the pore pressure within the sample is investigated by comparing values of effective vertical stress calculated using a linear equation published by Wissa et al. in 1971 with values of effective stress at the base of the specimen determined from measured values of pore pressure. Overall, the proposed method predicts the maximum allowable strain rate very well for three of the four soils and moderately well for the other soil.

DESIGN OF A LOAD CELL WITH LARGE OVERLOAD CAPACITY

To increase the signal-to-noise (S/N) ratio and sensitivity of a load cell, it is desirable to design a structure that generates large strain close to maximum allowable strain of the sensor material for a given rating load force. However, accommodating the margin of safety with respect to overloading, compromises the sensitivity. This paper presents the design, analysis, and prototype testing of a load cell which can provide large overload protection capacity without compromising the sensitivity of the sensor. This is achieved by a special design of sensor structure that becomes virtually rigid after its flexures reach their maximum deflection, thereby the sensor can be protected against a large over load. The sensor dimensions, which maximizes the sensor’s sensitivity, for given values of rating load and overload are obtained through mechanical strength analysis. A load cell prototype is fabricated and then tested to measure its linearity and overload characteristics. The experimental results show an accuracy of 0.2% of full scale and overload protection of the sensor flexures.

Mechanism of creep deformation of Alloy 230 based on microstructural analyses

Creep testing of Alloy 230 was performed at 750, 850 and 950 °C under applied stresses equivalent to its 10% and 25% yield strength (YS) values. The results indicate that this alloy satisfied the maximum allowable creep strain of 1% when loaded to 0.10YS level at these temperatures. Microscopic evaluations revealed the formation of second phase particles including superstructures and carbide precipitates as a function of temperature. The enhanced plastic strain at 0.25YS stress level at 950 °C was attributed to dislocation glide, subgrain formation, and recrystallization.

Analyzing of Stainless Elliptical Cup Drawing Process

A methodology of formulating an incremental elasto-plastic three-dimensional finite element model, which is based on Prandtl-Reuss flow rule and von Mises’s yield criterion respectively, associated with an updated Lagrangian formulation, is developed to simulate elliptical cup drawing process. An extended algorithm is proposed to formulate the boundary conditions, such as the yield of element, maximum allowable strain increment, maximum allowable rotation increment, maximum allowable equivalent stress increment, and tolerance for nodes getting out of contact with tool. In order to verify the reliability and accuracy of the FEM code, the fractured thickness of a specimen in the simple tension test is adopted as the fracture criterion of forming limit in simulation. A set of tools was designed to perform the elliptical cup drawing experiment on the hydraulic forming machine. According to the simulation and experimental results, the limit drawing ratio (LDR) amounts to about 2.136 for penetration in the elliptical cup drawing process of this study. This paper also found a comparison of the LDR of different tool radii. According to the definition of LDR, when the die radius is increased from R3.0mm to R9.0mm, the LDR would increase from 2.11 to 2.157. When the punch radius is increased from r3.0mm to r9.0mm, the LDR would increase from 2.07 to 2.181. This paper has provided a better understanding of the elliptical cup drawing process for improving the manufacturing processes and the design of tools.