Failure Strain Values Research Articles

An Criterion to Minimize FE Mesh-Dependency in Concrete Plate under Impact Loading

In the context of an increasing need for safety in concrete structures under blast and impact loading condition, the behavior of concrete under high strain rate condition has been an important issue. Since concrete subjected to impact loading associated with high strain rate shows quite different material behavior from that in the static state, several material models are proposed and used to describe the high strain rate behavior under blast and impact loading. In the process of modelling high strain rate conditions with these material models, mesh dependency in the used finite element(FE) is the key problem because simulation results under high strain-rate condition are quite sensitive to applied FE mesh size. This paper introduces an criterion which can minimize the mesh-dependency of simulation results on the basis of the fracture energy concept, and HJC(Holmquist Johnson Cook) model is examined to trace sensitivity to the used FE mesh size. To coincide with the purpose of the perforation simulation with a concrete plate under a projectile(bullet), the residual velocities of projectile after perforation are compared. The analytical results show that the variation of residual velocity with the used FE mesh size is quite reduced and accuracy of simulation results are improved by applying a unique failure strain value determined according to the proposed criterion.

Tensile Properties and Biocompatibility of Indonesian Wild Silk Cricula Trifenestrata: A Preliminary Study

As it is reported in many publication about successful work of many research in developing biomaterial from Bombyx mori silk which is attract many researchers to observe the possibilities in using different type of the silk other than Bombyx mori for biomaterial. Wild silks which is a silk that is not obtained from domesticated species are become object to explorer for better result for biomaterial. This research focused on Wild silk cocoon of Cricula trifenestrata obtained from Indonesian source. In this study the degumming process to separate the fiber from the cocoon was explored and the result is a separated fiber that is tested for its tensile strength and biocompatibility. It can be concluded that the silk obtained from cocoon of Cricula trifenestrata has good biocompatibility properties. The silk can be prepared by degumming method of boiling in 0.01 M NaOH for 1 hour. The modulus elasticity of the single fiber of Cricula trifenestrata is about 3681 MPa. The ultimate tensile strength is obtained about 162 MPa together with value of failure strain about 0.12. 

Research on Basalt Fiber Asphalt Concrete's Low Temperature Performance

Conduct experimental study on low temperature performance about asphalt concrete with 6mm basalt fiber and without basalt, 6mm fibers whose dosage is 0.12%0.15% and 0.17%, test method is the indirect tensile test,test temperature is-10±0.5°C. The results show that basalt fiber improved the strength and failure strain of asphalt concrete in low temperature damage, reduced the failure stiffness,in which the maximum increased value of breaking strength is 3.41%, the maximum increased value of failure strain is 38.83%,and the maximum reduced value of failure stiffness is 25.52%,obviously improved low temperature cracking resistance of asphalt concrete;for low temperature performance, the optimum amount of value about 6mm basalt fiber is 0.15% .

Mechanical Properties of Graphene Nanowiggles

ABSTRACTIn this work we have investigated the mechanical properties and fracture patterns of some graphene nanowiggles (GNWs). Graphene nanoribbons are finite graphene segments with a large aspect ratio, while GNWs are nonaligned periodic repetitions of graphene nanoribbons. We have carried out fully atomistic molecular dynamics simulations using a reactive force field (ReaxFF), as implemented in the LAMPPS (Large-scale Atomic/Molecular Massively Parallel Simulator) code. Our results showed that the GNW fracture patterns are strongly dependent on the nanoribbon topology and present an interesting behavior, since some narrow sheets have larger ultimate failure strain values. This can be explained by the fact that narrow nanoribbons have more angular freedom when compared to wider ones, which can create a more efficient way to accumulate and to dissipate strain/stress. We have also observed the formation of linear atomic chains (LACs) and some structural defect reconstructions during the material rupture. The reported graphene failure patterns, where zigzag/armchair edge terminated graphene structures are fractured along armchair/zigzag lines, were not observed in the GNW analyzed cases.

Numerical Analysis of Deformation and Failure of Penetration into Concrete Target by Projectile

Penetration is an important topic in the military and protection engineering field. Based on *MAT_PLASTIC_KINEMATIC of LS-DYNA program, this report studies effects of failure strain of the material parameters on structure of penetrating projectile. By establishing a group of numerical models about 45 steel hemispherical projectile penetrating semi-infinite concrete targets, this research aimed at analyzing effects of different failure strain values related to the destruction of the internal bracket structures of this projectile. At the same time, it studied the criterion of failure on finite dynamic program. The numerical results show that the use of failure strain in this model can well simulate damage of internal bracket structures of the projectile. Test was carried on based on this conclusion, which showed that bracket plate is subjected to shear failure in process of penetration, and numerical simulation was consistent with the experimental results.

Nonlinear failure analysis of carbon nanotubes by using molecular-mechanics based models

Equivalent nonlinear fracture models for pristine and reconstructed one- and two-atom vacancy defected single wall carbon nanotubes are developed by using the molecular mechanics based models where the initial reconstructed nanotube models are obtained by using molecular dynamic simulations and nonlinear characteristic of the covalent bonds are obtained by using the modified Morse potential. As a result of analyses, it is concluded that fractures of all types of nanotubes are brittle, armchair nanotubes are stiffer than zigzag nanotubes and vacancy defects significantly affect the mechanical behavior of nanotubes. In brief, fracture stress and strain values of pristine armchair nanotubes are respectively 30% and 32% larger than those of pristine zigzag nanotubes, and predicted failure stress and strain values of vacancy defected nanotubes are respectively 27% and 52% smaller than those of pristine ones. It is shown that large deformation and nonlinear geometric effects are important on fracture behavior of nanotubes. Comparisons are made with the failure stress and strain results reported in literature that show good agreement with our results.

Thermomechanical Behavior of Developmental Thermal Barrier Coating Bond Coats

Thermal expansion, microtensile, and stress relaxation experiments have been performed to contrast and compare the thermal and mechanical response of two experimental (L1 and H1) coatings provided by Honeywell Corporation (Morristown, NY). Thermal expansion experiments reveal that both coatings have coefficients of thermal expansion (CTE) that vary with temperature and that the CTE mismatch between the coatings and superalloy substrate is significant in the case of L1 as compared to H1. Values of the 0.2% offset yield stress (YS), Young’s modulus (E), and hardening exponent (n) are reported. Room-temperature microtensile experiments show higher strain hardening and a very low value of failure strain for L1 as compared to H1. At elevated temperatures, there is a significant decrease in the YS of as-received L1 for (924 MPa at room temperature to 85 MPa at 1000°C) as compared to H1. Finally, a power law creep description for high-temperature stress relaxation is developed and the measured values of the stress exponent (n = 3) and activation energies (Qcreep = 200–250 kJ/mol) are shown to be consistent with power law creep.

Tensile Characteristics of Coconut Fibers Reinforced Mortar Composites

Natural fibers such as coconut fibers are numerous in Indonesia. The tensile strength of coconut fibers produced in this country is among the highest of natural fibers ones. This paper is to determine the tensile strength of coconut fibers with or without special treatment (water washing dry) and assessment the ability of coconut fiber for reinforcement in mortar composites. Experimental observations on coconut fibers and mortars carried out. There were tensile tests and scanning electron microscopy (SEM) providing microstructural properties of coconut fibers. The results showed that the coconut fibers treatment increases tensile strength and provides higher failure strain values. It showed that coconut fibers largely improved tensile strength behavior of mortar composites. To a conclusion, the coconut fibers are able to be used as reinforcement for ductile mortar composites.

Effect of crosslinking and long-term storage on the shape-memory behavior of (meth)acrylate-based shape-memory polymers

This work highlights the free- and fixed-strain shape-memory response of amorphous (meth)acrylate-based shape-memory polymers as the level of crosslinking is varied from uncrosslinked to highly crosslinked (corresponding to a decrease in failure strains and overall increase in rubbery moduli and failure stresses). The effect of long-term storage on the free-strain shape-memory response is also considered. Tensile deformation levels during the shape-memory cycle are 90% of failure strain values to determine the full extent of free- and fixed-strain recovery behavior. All materials demonstrate full shape-recovery under free-strain conditions (material is unconstrained during recovery); however, total recoverable strains increase with decreasing crosslinking level, with uncrosslinked and lightly crosslinked materials recovering strains on the order of 3–10× that of moderately and highly crosslinked materials. In contrast, under fixed-strain conditions (material is fully constrained in the fixed shape during recovery), the magnitude of recovery stress generation increases with increasing crosslinking level, with highly crosslinked materials demonstrating recovery stress levels 4–20× that of lightly crosslinked and uncrosslinked materials. The ability to produce recovery stresses on par with those reached during deformation also increases with crosslinking level. Stored-shape fixation and free-strain recovery levels remain stable after long-term storage in the deformed temporary state at 20 °C; however, recovery onset temperatures increase (by up to 9 °C) with storage time spanning ∼1 year, as do rates of free-strain recovery (by up to 9×), due to physical aging. Results indicate that aging could potentially be used as a method for shape-memory response optimization.

Relation Between Normalized Axial Stress and Failure Strain in Heterogeneous Carbonate Rocks Exhibiting Large Axial Strains

A semi-analytical equation for the modeling of stress–strain relationship for heterogeneous carbonate rocks exhibiting large axial strains (eaf > 1%) is formulated. The equation is derived by modifying the stress–strain model based on Haldane’s distribution proposed by Palchik (2006) for carbonate rocks exhibiting e af ≤ 1%. The developed exponential model is used to relate normalized axial stress (σ a/σ c) over the whole pre-failure strain range to current axial strain (e a) and failure strain (e af). For carbonate rocks exhibiting e af > 1%, the value of pre-calculated parameter δ involved in the stress–strain model is not constant, but dependent on the failure strain value (e af). The normalized stress–strain model can be used to calculate the failure strain in terms of uniaxial compressive strength and stress–strain measurement at one point only. The advantages of the failure strain model and ways of its use in engineering practice are discussed.

Investigation of rain erosion on a brittle material by means of numerical simulation

In this work, the resistance and deformation characteristics of a brittle material against rain erosion are examined by using the non-linear, explicit software LS-DYNA. The water jet with varying speeds impinges at 90° on silica float glass plates with different thicknesses. In the simulations, the Arbitrary Lagrangian Eulerian method is used for modelling of the water. In order to analyse the deformations on the brittle material Johnson–Holmquist–Ceramics (JH-2) is used as the material model. Minimum plate thickness (for constant water jet speed) and maximum water speed (for constant plate thickness), which do not cause any damage to the target, are determined depending on the geometry, boundary conditions and assumed failure strain value for erosion. The results are compared with the water-hammer pressure.

조선 해양 구조물용 강재의 소성 및 파단 특성 I: 변형률 경화 및 변형률 속도 경화의 이론적 배경

*Dep't of Naval Architecture and Ocean Engineering, Inha Univer sity, Incheon, Korea**Dep't of Naval Architecture and Marine Engineering, Mokpo Nat ional University, Mokpo, KoreaKEY WORDS: Plasticity 소성, Strain hardening 변형률 경화, Strain rate hardening 변형률 속도 경화, Fracture 파단, True stress 진응력ABSTRACT: In this paper, the global study trends for material behaviors a re investigated regarding the static and dynamic hardenings and final fractures of marine structural steels. In particular, after rev iewing all of the papers published at the 4th and 5th ICCGS (In ternational Conference on Collision and Grounding of Ship), the used hardening and fra cture properties are summarized, explicitly presenting the mate rial properties. Although some studies have attempted to employ new plasticity a nd fracture models, it is obvious that most still employed an i deal hardening rule such as perfect plastic or linear hardening and a simple shear fracture criterion with an assumed value of failure strain. HSE (2001) presented pioneering study results regarding the temperature dependency o f material strain hardening at various levels of temperature, b ut did not show strain rate hardening at intermediate or high strain rate range s. Nemat-Nasser and Guo (2003) carried out fully coupled tests for DH-36 steel: strain hardening, strain rate hardening, and temperature harden ing and softening at multiple steps of strain rates and tempera tures. The main goal of this paper is to provide the theoretical background for stra in and strain rate hardening. In addition, it presents the procedure and methodology needed to derive the material constants for the static hardenin g constitutive equations of Ludwik, Hollomon, Swift, and Ramber g-Osgood and for the dynamic hardening constitutive equations of power from Cowper-S ymonds and Johnson-Cook.교신저자 정준모: 인천광역시 남구 용현동 253, 032-860-7346, jmchoung@inha.ac.kr

Numerical study on concrete penetration/perforation under high velocity impact by ogive-nose steel projectile

Severe element distortion problem is observed in finite element mesh while performing numerical simulations of high velocity steel projectiles penetration/perforation of concrete targets using finite element method (FEM). This problem of element distortion in Lagrangian formulation of FEM can be resolved by using element erosion methodology. Element erosion approach is applied in the finite element program by defining failure parameters as a condition for element elimination. In this study strain parameters for both compression and tension at failure are used as failure criteria. Since no direct method exists to determine these values, a calibration approach is used to establish suitable failure strain values while performing numerical simulations of ogive-nose steel projectile penetration/perforation into concrete target. A range of erosion parameters is suggested and adopted in concrete penetration/perforation tests to validate the suggested values. Good agreement between the numerical and field data is observed.

Low-temperature tensile behaviour of asphalt binders: Application of loading time–temperature–conditioning time superposition principle

Thermal cracking of bituminous layers is one of the main modes of failure for asphalt pavements. This distress is highly related to the rheological properties of asphalt binders. The purpose of this study was to investigate the low-temperature behaviour of asphalt binders by performing Direct Tension Tests (DTTs) according to Superpave specification. The DTT results were analyzed and compared in terms of trend of stress–strain curve instead of conventional failure stress or failure strain values. Through the analysis of stress–strain diagram, it was possible to evaluate the effects of temperature, elongation rate and conditioning time on the rheological properties of binders. Particular attention was paid to the conditioning time variable as it was observed that the stiffness of the binder changes with time when it is stored isothermally at low temperature due to the physical hardening phenomenon. To this end, a modified superposition effects principle, which also includes the conditioning time in addition to the temperature and elongation rate variable, has been proposed. Finally, this principle allowed the authors to find an analytical model capable of describing the rheological properties of asphalt binders as functions of the three considered test variables.

An experimental study on influences of material brittleness on chip morphology

Though several material properties such as hardness, thermal conductivity, specific heat, strain hardening, and thermal softening ability have been studied in terms of influencing segmental or serrated chip formation process, rare study about material brittleness affecting the chip formation process has been carried out. In this paper, an orthogonal cutting experiment with four steels with different brittleness was carried out. The effect of workpiece material brittleness on segmental chip formation and consequent chip morphology was investigated. The experimental results show that the material brittleness heavily affects chip formation process and chip shape. A novel chip formation model was developed to explain the mechanism of material brittleness working on the chip formation process. The mechanism is that material brittleness lowers the value of failure strain and thus makes the maximum stress in flow stress curve occur earlier, which leads to the catastrophic shear instability in primary shear zone and consequent segmented chip.

Standardization of Test Procedure for Tension Test on Coir Yarns and Woven Coir Geotextiles

Abstract This paper presents the results of an experimental investigation conducted to develop a standard test procedure for tension testing on coir yarns and woven coir geotextiles. Uniaxial tension tests were conducted on nine types of woven coir geotextiles and eleven types of coir yarns. Specimens of different dimensions were tested at various deformation rates. Test results indicated that tensile properties of coir yarns and geotextiles were largely influenced by testing parameters. Statistical analysis of yarn tension data was carried out to establish the gauge length, strain rate, and specimen dimensions of geotextiles. Consistent values of tensile strength and failure strain were obtained when gauge length and strain rate were adopted as 150 mm and 5 %/min, respectively. It was also observed that reliable results were obtained when the width of the geotextile specimen for tension test contained not less than ten yarns.

Numerical analysis of chip formation during machining for different value of failure strain

AbstractGrinding is a very complicated processing. To increase quality of product and minimize the cost of abrasive machining, we should know physical phenomena which exist during the process. The first step to solution of this problem is analysis of machining process with a single abrasive grain. In the papers [1, 2] the thermo‐mechanical models of this process are presented, but in this work attention is concentrated on chip formation and his separation from object. The influence of failure strain εf on states of strain and stress in surface layer during machining is explained. The phenomena on a typical incremental step were described using step‐by‐step incremental procedure, with updated Lagrangian formulation. Then, the Finite Element Method (FEM) and Dynamic Explicit Method (DEM) were used to obtain the solution. Application was developed in the ANSYS system, which makes possible a complex time analysis of the physical phenomena: states of displacements, strains and stress. Numerical computations of the strain have been conducted with the use of two methodologies. The first one requires an introduction of boundary conditions for displacements in the contact area determined in modeling investigation, while the second – a proper definition of the contact zone through the introduction of finite elements of TARGET and CONTACT types, without the necessity to introduce boundary conditions. This model includes variational equations of the object's motion and deformation. Examples of calculations for the displacement, strain and stress field in the surface layer zones were presented. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

High strain rate behavior of 4-step 3D braided composites under compressive failure

The out-of-plane and in-plane compressive failure behavior of 4-step 3D braided composite materials was investigated at quasi-static and high strain rates. The out-of-plane and in-plane direction compressive tests at high strain rates from 800/s to 3,500/s were tested with the split Hopkinson pressure bar (SHPB) technique. The quasi-static compressive tests were conducted on a MTS 810.23 tester and compared with those at high strain rates. The comparisons indicate that the failure stress, failure strain and compressive stiffness both for out-of-plane and in-plane loading directions are rate sensitive. For example, the failure stress, failure strain and stiffness are 55.19 MPa, 6.70% and 1.35 GPa respectively as opposed to 145.00 MPa, 1.21% and 13.50 GPa respectively for strain rate of 2,500 s−1 under in-plane compression. The 3D braided composites have higher values of failure stress and strain for out-of-plane than for in-plane compression at the same strain rate; however, the in-plane compression stiffness is higher than that of out-of-plane compression at high strain rates. The compressive failure mode of 3D braided composites in the out-of-plane direction is mainly shear failure at various strain rates, while for the in-plane direction it is mainly cracking of matrix.

The Effect of Ti–B and Sr on the mechanical behaviour of the Zinc–Aluminum-based ZA-12 alloy produced by gravity casting

Abstract In this study, the effect of Ti–B (0.05–0.7wt.% Ti, 0.01–0.13wt.% B) and Sr additions (0.05–0.7wt.%) on the hardness, ultimate tensile strength (UTS), strain and fatigue properties of the gravity cast Zn–Al-based ZA-12 alloy was investigated. While the Ti–B additions had no significant effect on the hardness of the alloys, the Sr additions lowered the hardness by a small amount. UTS and fatigue resistance of the ZA-12 alloy increased with 0.05wt.% Ti, but the addition of 0.05wt.% Sr to the standard alloy did not change these properties significantly. In excess of 0.05wt.% Ti and Sr, the UTS and fatigue resistance of the alloys decreased and reached a lower value than that of the standard alloy. The failure strain only increased for the ZA-12 alloy containing 0.05wt.% Ti, then decreased with further increase in Ti content. The failure strain values of the alloys decreased with addition of Sr. Metallographic examination indicated that the addition of Ti–B strongly modified the microstructure of the standard ZA-12 alloy, but Sr did not. Ti and Sr have also formed complex-shaped intermetallic compounds, which were identified as Al5Ti2Zn and Zn5Al3Sr by X-ray diffraction and EDS analyses. It can be suggested that these particles cause a decrease in UTS, fatigue resistance, and strain to failure of the ZA-12 alloy.

Modelling the area expansion ratio on uniaxial compression of cylindrical potato samples

Uniaxial compression tests were performed on potato flesh. Cylindrical samples of heights (5, 10, 15 and 20 mm) and diameters (25.4 and 19.05 mm) were tested under lubricated (mineral oil), non-lubricated (natural) and increased friction (emery paper) conditions. Sample flatness (force free area/loaded area) ranged between 0.79 and 4.20. Deformation rate effect was also examined by performing compression tests at 50, 100, 200 and 400 mm min −1. In this study, parameter derived from compression to failure was failure strain ( ε r %). It was established a method for determining the area expansion ratio, AF/ A 0 (actual maximum area in contact with the loading platens/original area) at several deformation levels ( ε %). For that, loaded area was determined at deformation levels (20%, 40% and 80%) by planimetring of a graphic mark, and then adjusted by regression with respect to deformation level. From this regression, area expansion ratio at failure, AF r/ A 0 was obtained by replacing at each equation corresponding failure strain value. Cylindrical potato samples compression was accompanied by a significant cross-sectional area expansion, evidencing a far-ideal area expansion. For lubricated and non-lubricated friction conditions, increasing deformation rate and sample diameter increased AF r/ A 0, whereas increasing sample height decreased the ratio, mainly under non-lubricated condition. Lubrication causes an increase of AF r/ A 0 average value, near 5% with respect to that obtained with non-lubricated friction condition, meaning a lower influence of deformation rate and sample height, but a higher flatness influence. Effect due to surface lubrication was smaller than in previous compression tests on cheeses, which could be attributed to release of fluid from the damaged tissue of the potato flesh which relatively reduced lubricant effectiveness.