Poisson's Ratio Values Research Articles

Evaluation of elastic properties of fiber reinforced concrete with homogenization theory and finite element simulation

This paper aims to evaluate the elastic modulus and Poisson ratio of fiber reinforced concrete with homogenization theory and finite element simulation. A theoretical model for predicting the elastic modulus and Poisson ratio of fiber reinforced concrete was established by homogenization theory. Firstly, the elastic tensor matrix of unidirectional distribution fiber reinforced concrete composites was solved by the composite cylinder model and Ruess series model, and then the elastic tensor matrix of random distribution of fiber reinforced concrete composites was obtained based on the probability density function of fiber distribution. Finally, the elastic modulus and Poisson ratio of fiber reinforced concrete were obtained based on the elastic tensor matrix. In addition, according to the related parameters of experiment, the random distribution meso-model of fiber reinforced concrete was established using MATLAB software, and then the axial compression of fiber reinforced concrete was stimulated using Abaqus. The simulation values of elastic modulus and Poisson ratio of fiber reinforced concrete were obtained. By comparison, it was found that the homogenization theoretical predicted value, the finite element simulation value and the macroscopic experiment value were in good agreement, which verified the accuracy of the homogenization theoretical model and the finite element model.

Auxetic Properties of a f.c.c. Crystal of Hard Spheres with an Array of [001]‐Nanochannels Filled by Hard Spheres of Another Diameter

Preliminary results on the influence of periodically distributed cylindrical nanoinclusions introduced into the f.c.c. hard sphere crystal on its elastic properties and the Poisson's ratio are presented. The nanoinclusions are oriented along the [001]‐direction and filled with hard spheres of diameter different from the spheres forming the matrix crystal. The Monte Carlo simulations show that symmetry of the crystal changes from the cubic to tetragonal one. In the case when spheres inside the inclusion are smaller than spheres forming the crystal, the changes of Poisson's ratio are qualitatively similar to the changes observed earlier in the Yukawa sphere crystal, that is, the introduction of nanochannels causes simultaneous decrease of the Poisson's ratio in the [110][10]‐direction, and its increase in [110][001]‐direction. Filling the nanochannel with spheres having diameters greater than that of the spheres in the crystalline matrix, causes a decrease of the Poisson's ratio value from 0.065 down to −0.365 in [111][11]‐direction. The dependence of the minimal Poisson's ratio on the direction of the applied load is shown in a form of surfaces in spherical coordinates, for selected values of nanochannel particle diameters. The most negative value of the Poisson's ratio found amongst all systems studied was as low as −0.873.

Study of Radial Vibrations in an Infinitely Long Fluid-Filled Transversely Isotropic Thick-Walled Hollow Composite Poroelastic Cylinders

Abstract In this paper, radial vibrations of an infinitely long fluid-filled transversely isotropic thick-walled hollow composite poroelastic cylinder are investigated in the framework of poroelasticity. The cylinder consists of two concentric cylindrical layers namely, core (inner one) and coating (outer one), each of which retains its own distinctive properties. A comparative study has been made between the thick-walled hollow composite poroelastic cylinder and that of fluid-filled one. Frequency is computed against the ratio between the thickness to inner radius of the composite cylinder at various anisotropic ratios. Another comparative study is made between the results of current case and that of isotropic case by making Young’s modulus and Poisson ratio values of isotropic and that of transversely isotropic in the transverse direction equal. Numerical results are depicted graphically and then discussed.

First-principles studies of Mg17Al12,Mg2Al3,Mg2Sn,MgZn2,Mg2Ni and Al3Ni phases

Thermal stabilities, electronic structures and elastic properties of Mg2Ni, Al3Ni, Mg2Sn, MgZn2, Mg17Al12 and Mg2Al3 have been determined from first-principle calculations. The calculated results of heats of formation and cohesive energies show that Al3Ni has the strongest alloying ability and structural stability. Gibbs free energy is calculated and discussed. The densities of states (DOS) and Mulliken electronic populations of these compounds are given. The elastic constants are calculated, the bulk moduli, shear moduli, Young's moduli and Poisson ratio value are derived, the brittleness and plasticity of these phases are discussed.

Mechanical Properties of Y2Al Crystal

The lattice parameters of the material were obtained by Quantum Espresso code in the GGA approach a = 12.4346580117 Bohr b / a = 0.7757687079 and c / a = 1.4439057035. In the calculations made, values of 50 Ry (ecutwfc), 175 Ry (ecutrho) were used. Anisotropy factor and linear compressibility were investigated. Elastic constants C11, C22, C33, C44, C55, C66, C12, C13 and C23 were determined with ElaStic software. Using these obtained elastic constants, bulk modulus (55.04 GPa), shear modulus (30.75 GPa), Young modulus (77.77 GPa) and Poisson's ratio (0.26) values were obtained in Hill approximation. The results were compared with current literature values.

A mathematical model for gas and water production from overlapping fractured coalbed methane and tight gas reservoirs

With the continuous expansion, exploration and development of unconventional natural gas resources, mainly coalbed methane, shale gas and tight gas, some areas overlapped by two or three types of unconventional natural gas reservoirs are explored, e.g., the Linxing, Shilou and Linfen blocks located in the east margin of the Ordos Basin, China. Gas extraction from an individual reservoir becomes not economic as gas resources are not fully recovered; thus, gas coproduction from two or multiple layers is an effective method for improving gas production. In this work, a mathematical model of gas and water two-phase flow for the coproduction of coalbed methane and tight gas is developed. The adsorption characteristics, stress-sensitive and matrix shrinkage effects on coal permeability, and the stress-sensitive effect of tight sandstone are all considered in the model. The gas production related parameters, such as bottom hole flowing pressure, reservoir pressure differences, reservoir properties (e.g., permeability, cleat compressibility of coal, and Langmuir isotherm parameters) are discussed and compared with different geological conditions. The results show that the gas and water flow from the coalbed and sandstone reservoirs show no interference between each other under a constant pressure drainage system; the sandstone reservoirs show a fast pressure drawdown with a high gas production rate decline, while the coalbed reservoir is slow in pressure drawdown and the gas production rate increases gradually. The properties of a specific reservoir have a great influence on its own gas production performance, but with no influence on the other reservoirs. It was found that a lower constant drainage pressure should be adopted in the case of stress-sensitive effects, and coal with a lower cleat compression coefficient and Poisson's ratio value is better for higher gas production. The production contribution from each layer can be acquired if a specific production rate is set. If the reservoir pressure difference between the two reservoirs is too high (for instance at least > 3 MPa in the cases studied in this work), gas and water intrusion may happen, but the reservoirs would be balanced quickly. Thus, the coproduction of coalbed methane and tight gas from one well bore is feasible, and more work should be conducted on proposing a proper drainage strategy to improve the gas resource recovery efficiency in coal-bearing strata.

Effect Bi2O3 on the physical, structural and radiation shielding properties of Er3+ ions doped bismuth sodiumfluoroborate glasses

Er3+ ions doped Bismuth sodiumfluoroborate glasses with varying Bi2O3 content (0−50 in wt%) have been prepared following the melt quenching technique. The density, molar volume, FTIR and UV–Visible studies have been used to determine physical and structural properties of the prepared glasses. The FTIR studies explores that, addition of Bi2O3 helps the progressive conversion of [BO4] units into [BO3] units thus lead to the creation of non-bridging oxygens (NBOs). The boron‑boron separation(<dB–B>), oxygen packing density(OPD), bond density(nb) and calculated Poisson's ratio (μcal) values are found to decrease with the addition of Bi2O3thus reveal the fact that the network connectivity decreases due to the formation of non-bridging oxygen sites and the glass network becomes less tightly packed. Further, ionic nature of the Er3+ − metal ligand bond was identified from the measured optical basicity (Λth), covalent and ionic characteristic factors, and bonding parameter (δ) values.The observed variations in the optical electronegativity, basicity, metallization criterion and optical band gap energy (Eg) values have been discussed in terms of the structural changes that takes place due to the addition of Bi2O3 into the B2O3 network. Additionally, radiation shielding properties of the prepared glasses have been studied in the energy range 0.015–15 MeV. The mass attenuation coefficient has been calculated using MCNP5 code and XCOM software. The MCNP5 results match most of the XCOM data very well. Further, the effective atomic number, mean free path and half value layer (HVL) for the titled glasses were computed. The mass attenuation coefficient and the effective atomic number were found to progressively increase with the increase in the Bi2O3 content. The addition of Bi2O3 led to decrease the half value layer which means that more Bi2O3 content enhances the radiation shielding performance for the prepared glasses.

Soil characterization of Bornova Plain (Izmir, Turkey) and its surroundings using a combined survey of MASW and ReMi methods and Nakamura’s (HVSR) technique

Structural damage which occurs during earthquakes is related to both the soil dynamic behavior attributes and soil response spectrums. Therefore, soil characterization based of S-wave velocity (Vs) is one of the prime factors to estimate damage and hazards. In this study, multi-channel analysis of surface waves (MASW) and refraction microtremor (ReMi) methods have been applied to estimate Vs values of the area located east of Izmir Bay. Based on the estimated Vs values, two- and three-dimensional shear-wave velocity and the maximum shear modulus maps at various depths down to 50 m were prepared. To study the relationship between the predominant period of the soil and shear-wave velocity values, a horizontal-to-vertical (H/V) spectral ratio method using Nakamura’s technique has been applied. Groundwater level, standard penetration test (SPT-N30) and Poisson ratio values were also obtained from previous geotechnical borehole data in the study area. In addition, we calculated building periods using the empirical relationship between height (or number of floors) of buildings and predominant period of the buildings to examine soil-structure resonance. According to the National Earthquake Hazard Reduction Program (NEHRP; 1997) soil classification, the study site consists of B-, C- and F-type soils. Risk maps were created using dynamic properties of the soil.

Full potential study of HoMg

Abstract In this paper, HoMg is studied in two different phases i.e. B1 and B2. The calculated lattice constants in B1 and B2 phases are 6.39 A and 3.78 A and corresponding energies are −25,648.49 Ry and −25,648.56 Ry, respectively. It is more stable in B2 phase (Pm-3m configuration with no. 221). The analysis of the obtained band structure and density of states shows metallic character of HoMg. Detailed information about the elastic properties is also presented in this paper. The calculated values of Cauchy pressure, G/B and Poisson ratio are −10.72, 0.58 and 0.26, respectively which indicates that HoMg have brittle character. Calculations for the optical spectra such as the components of dielectric function, refractive index and other parameters of the optical properties are performed in the energy range of 0–20 eV. For HoMg, the main peak of absorption spectra and energy loss function is located at 7.44 eV and 11.76 eV, respectively. Thermal parameters such as Gruneisen parameter, Debye temperature, Specific heat etc. have been reported as a function of pressure and temperature.

Deformation and cracking behavior of La2O3-doped oxide glasses with high Poisson's ratio

Oxide glasses pose high theoretical strength originating from their strong ionocovalent bonding, but they experience amplification of tensile stresses around defects under tensile loading and lack efficient stress dissipation mechanisms. Consequently, glasses exhibit low practical strength and fracture toughness, limiting the scope of their applications. Different strengthening and reinforcement approaches have thus been tested, but relatively little success has been achieved with respect to making the glasses intrinsically more ductile through composition optimization. Following earlier literature reports, a possible route to achieve this would be to prepare glasses with high Poisson's ratio above ~0.32. Yet, no oxide glasses with such high Poisson's ratio have been reported and the mechanical properties of oxide glasses with Poisson's ratio ≥ 0.30 are poorly understood. In this paper, we synthesize 25%La2O3–15%Al2O3–60%B2O3, 25%La2O3–15%Al2O3–60%SiO2, and 25%La2O3–15%Al2O3–60%GeO2 glasses (fractions in mol%), all exhibiting high Poisson's ratio values (~0.30). We evaluate the mechanical properties, including elastic moduli, Poisson's ratio, hardness, and resistance to indentation cracking of the as-prepared as well as densified glasses. In addition, the indentation deformation mechanism of the glasses along with the accompanying underlying structural changes is investigated. This study therefore presents insight into the composition-property relations of high Poisson's ratio glasses, which may be used in future design of ductile oxide glasses with potential applications in electronic devices, optical fibers, and load-bearing components of buildings or other constructions.

Enhancing the mechanical properties of virgin and damaged jute/polypropylene hybrid nonwoven geotextiles via mild alkali treatment of jute fibers

Nonwoven geotextiles made from hybridization of natural and synthetic fibers can potentially offer distinct advantages in terms of uniformity and improved mechanical properties. To further enhance the mechanical properties of hybrid nonwoven geotextiles, natural fibers such as jute must be treated with a minimal amount of alkali, such that the treatment process becomes scalable, cost-effective and environmentally friendly. Herein, we report a comparative analysis of physical and mechanical properties between the corresponding samples of untreated (UT) jute/polypropylene (PP) and mild alkali-treated (MAT) jute/PP nonwoven geotextiles in both virgin and damaged conditions. The constituent jute fibers were treated with 0.5 wt.% of sodium hydroxide solution under ambient temperature conditions for 24 h duration. Such mild treatment of jute fibers with alkali solution resulted in considerable improvement in the mechanical properties of MAT jute/PP nonwoven geotextiles corresponding to the sets of UT jute/PP nonwoven geotextiles. Various types of damage, including circular holes, horizontal cuts, vertical cuts and inclined cuts at an angle of 45°, were artificially induced in hybrid nonwoven geotextiles to investigate the reduction in tensile properties. Further, the Poisson's ratio in virgin and damaged states was determined to make a comparison between the UT and MAT jute/PP nonwoven geotextiles. In general, lower Poisson's ratio values were observed for mechanically damaged MAT jute/PP nonwoven geotextiles corresponding to the samples of UT jute/PP nonwoven geotextiles. Surprisingly, the vertical cuts induced in MAT jute/PP nonwoven geotextiles yielded tensile strength comparable to that of virgin samples.

MOPSO: a new computing algorithm for joint inversion of Rayleigh wave dispersion curve and refraction traveltimes

Adequate estimation of shear-wave (VS) and P-wave (VP) velocity profiles is one of the significant objectives in the course of seismic surveys; however, the main problem in obtaining VS and VP is the non-uniqueness of surface waves and refracted seismic inversion results. Moreover, the hidden-layer problem often exists in the case of the refraction seismic method. The main purpose of this study is to cope with the above problems and reconstruct subsurface structures by joint inversion of Rayleigh wave dispersion curve and refraction traveltimes. The proposed joint inversion is based on a multi-objective particle swarm optimisation (MOPSO) strategy as a new tool for joint inversion of seismic datasets. The Pareto front concept was applied in the proposed joint inversion scheme. Using the Pareto front, the presented inversion algorithm provided a useful tool to evaluate the results (i.e. the number of layers, thicknesses or Poisson ratio values for the estimated models). The proposed algorithm was tested on two synthetic datasets and also on an experimental dataset. Furthermore, the joint inversion results were compared with the results of individual datasets inverted using PSO inversion algorithm. To verify the applicability of the proposed method, it was applied at a sample site located in Tabriz city, north-western Iran. For a real dataset, the refraction microtremor (ReMi) was used to obtain Rayleigh wave dispersion curves. Moreover, sourced from a vertical-incident seismic source (sledgehammer), seismic refraction data were recorded via vertical component geophones. The results showed that the proposed joint inversion technique can considerably reduce uncertainties of the inverted models.

Sensitivity of elastic parameters during the numerical simulation of pharmaceutical die compaction process with Drucker-Prager/Cap model

Numerical simulation of the die compaction process with Drucker-Prager/Cap (DPC) model is increasingly used to understand the powder behavior during compression. The use of DPC model to numerically simulate the powder compression requires the characterization of a number of parameters like the DPC model parameters, the elastic parameters and the friction coefficient.The methods used to characterize the required parameters are well detailed in the literature. Nevertheless, the values determined for a given parameter of a product varies from a study to another. The effects of the variations of some plastic parameters were already studied in the literature, but the influence of elastic parameters has not been assessed. Then, to investigate such an influence, in this article, we have used already published values for the elastic parameters of microcrystalline cellulose. Moreover, realistic deviations of the values of Young's modulus and Poisson's ratio, based on the differences observed in the literature were introduced in the numerical simulation performed with the Drucker-Prager/Cap (DPC) model and their effects on the results were analyzed.The results show that the variation of the Young's modulus E has no influence on the distribution of the relative density, the axial and radial stresses and on the final tablet thickness. On the other hand, variations of the Poisson's ratio lead to a change of the results of the compaction. The residual radial stresses are low when high Poisson's ratio values are used in the simulation. In particular the residual die wall pressure decreases and tends towards zero when the Poisson's ratio increases. In the case of simultaneous variations of the Young's modulus and the Poisson's ratio, the effects on the numerical results are principally due the change of the Poisson's ratio. Nevertheless, the elastic recovery is more important when the values of the two parameters are low.This work clearly highlights a link between the Poisson's ratio and the residual die wall pressure. Since a correlation was established between the die wall pressure and the occurrence of some defects like capping, it is important to well characterize the Poisson's ratio for a good prediction of capping phenomena when using FEM modeling.

Stress-controlled Poisson ratio of a crystalline membrane: Application to graphene

We demonstrate that a key elastic parameter of a suspended crystalline membrane---the Poisson ratio (PR) $\nu$---is a non-trivial function of the applied stress $\sigma$ and of the system size $L$, i.e., $\nu=\nu_L(\sigma)$. We consider a generic 2D membrane embedded into space of dimensionality $2+d_c$. (The physical situation corresponds to $d_c=1$.) A particularly important application of our results is free-standing graphene. We find that at very low stress, where the membrane exhibits a linear response, the PR $\nu_L(0)$ decreases with increasing $L$ and saturates for $ L\to \infty$ at a value which depends on the boundary conditions and is essentially different from the value $\nu=-1/3$ previously predicted by the membrane theory within a self-consisted scaling analysis. By increasing $\sigma$, one drives a membrane into a non-linear regime characterized by a universal value of PR that depends solely on $d_c.$ This universal non-linear PR acquires its minimum value $\nu_{\rm min}=-1$ in the limit $d_c\to \infty.$ With the further increase of $\sigma$, the PR changes sign and finally saturates at a positive non-universal value prescribed by the conventional elasticity theory. We also show that one should distinguish between the absolute and differential PR ($\nu$ and $\nu^{\rm diff}$, respectively). While coinciding in the limits of very low and very high stresses, they differ in general, $\nu \neq \nu^{\rm diff}$. In particular, in the non-linear universal regime, $\nu^{\rm diff}$ takes a universal value which, similarly to absolute PR, is a function solely of $d_c$ but is different from the universal value of $\nu$. In the limit $d_c\to \infty$, the universal value of $\nu^{\rm diff}$ tends to $-1/3$, at variance with the limiting value $-1$ of $\nu$. Finally, we briefly discuss generalization of these results to a disordered membrane.

Evaluation of the residual stresses in 95wt%Al2O3-5wt% SiC wear protection coating using X-Ray diffraction technique

This paper aims to measuring the residual stresses practically in wear protection coatings using the sin2ψ method according to X-ray diffraction technique. The wear protection coatings used in this study was composite coating 95wt% Al2O3-5wt% SiC, while bond coat was AlNi alloy produced by using flame spraying technique on the mild steel substrate. The diffraction angle, 2θ, is measured experimentally and then the lattice spacing is calculated from the diffraction angle, and the known X-ray wavelength using Bragg’s Law. Once the dspacing values are known, they can be plotted versus sin2ψ, (ψ is the tilt angle). In this paper, stress measurement of the samples that exhibit a linear behavior as in the case of a homogenous isotropic sample in a biaxial stress state is included. The plot of dspacing versus sin2ψ is a straight line which slope is proportional to stress. On the other hand, the second set of samples showed oscillatory dspacing versus sin2ψ behaviour. The oscillatory behaviour indicates the presence of inhomogeneous stress distribution. In this case the X-ray elastic constants must be used instead of Young’s modulus (E) and Poisson ratio (ν)values. These constants can be obtained from the literature for a given material and reflection combination. The value of the residual stresses for the present coating calculated was compressive stresses (-325.6758MPa).

Evolutionary design of nonuniform cellular structures with optimized Poisson's ratio distribution

For negative Poisson's ratio (NPR) cellular structures, most previous research focus on the design of unit cells, and then repeat the unit cell to construct uniform cellular structures. However, there is a disadvantage that these structures do not have much design freedom to achieve high-level functions, such as performing a desired deformation. As a solution, an evolutionary design method is proposed to develop nonuniform cellular structures. To conduct this method, the design domain is divided into finite unit cells with tunable Poisson's ratio (PR). With a given objective deformation, the value of each unit cell's PR is optimized using evolutionary algorithm (EA). In order to reduce the computational cost of the algorithm, discrete cosine transform (DCT) is applied to encode the structure for evolving. Considering the geometrical complexity of the optimized nonuniform cellular structures, additive manufacturing (AM) is chosen to build them physically. Both two-dimensional (2D) and three-dimensional (3D) design cases were developed and analyzed to validate the proposed method. The computational and experimental results showed good conformation with each other. Most importantly, this novel design method brings huge potential to NPR cellular structures with high-level functions and much wider applications.

A new numerical investigation of cement sheath integrity during multistage hydraulic fracturing shale gas wells

Volume fracturing of shale gas wells has been observed to lead to the failure of cement sheath and to sustained casing pressure (SCP). This paper presents a new numerical investigation aimed at understanding the failure mechanism of the cement sheath during volume fracturing. A wellbore temperature model was established to obtain the required input parameters for the dynamic temperature boundary. The numerical model considers the coupling of casing, cement sheath, and formation rock to calculate the radial and tangential stresses in the cement sheath. In addition to the cement mechanical properties, the influencing factors considered include the casing pressure, fracturing fluid displacement, and initial temperature. The cement sheath integrity was evaluated using the Mohr-Coulomb failure criterion. The results show that the temperature of cement sheath changes drastically during fracturing. The radial and tangential stresses in the cement sheath change continuously with time. Lowering the internal wellbore pressure can effectively reduce the radial and tangential stresses in the cement sheath. Reducing the fracturing fluid displacement can significantly lower the radial and tangential stresses in the cement sheath. Increasing the initial fracturing fluid temperature will cause the radial stress of cement sheath to increase and the tangential stress to decrease. The use of cements with low Young's modulus values can significantly reduce the radial and tangential stresses in the cement sheath. The use of cements with low Poisson's ratio values can lower the tangential stress. The results obtained using the model were verified by field data that demonstrated no occurrence of casing pressure when using a cement with a low elastic modulus, as suggested by the model.

Effect of far-field stresses and residual stresses incorporation in predicting fracture toughness of carbon nanotube reinforced yttria stabilized zirconia

Yttria-stabilized zirconia (YSZ) is a potential thermal insulating ceramic for high temperature applications (&amp;gt;1000 °C). YSZ reinforced with multi-walled carbon nanotubes (MWNTs) was processed via spark plasma sintering to produce dense, crack-free homogeneous sample and avoid any degradation of MWNTs when sintered using conventional routes. Despite porosity, the addition of MWNT has a profound effect in improving the damage tolerance of YSZ by allowing the retention of tetragonal phase. However, at some instances, the crack lengths in the MWNT reinforced YSZ matrices have been found to be longer than the standalone counterparts. Therefore, it becomes inappropriate to apply Anstis equation to calculate fracture toughness values. In this regard, a combined analytical cum numerical method is used to estimate the theoretical fracture toughness and quantitatively analyze the mechanics of matrix cracking in the reinforced composite matrices incorporating the effects of various factors (such as far-field stresses, volume fraction of MWNTs, change in the modulus and Poisson's ratio values along with the increase in porosity, and bridging and phase transformation mechanism) affecting the fracture toughness of YSZ-MWNT composites. The results suggest that the incorporation of far-field stresses cannot be ignored in estimating the theoretical fracture toughness of YSZ-MWNT composites.

The effect of fluid and solid properties on the auxetic behavior of porous materials having rock-like microstructures

Materials with a negative Poisson's Ratio (PR), known as auxetics, exhibit the counterintuitive behavior of becoming wider when uniaxially stretched and thinner when compressed. Though negative PR is characteristic of polymer foams or cellular solids, tight as well as highly porous rocks have also been reported to exhibit negative PR. The paper proposes a novel auxetic structure based on pore-space configuration observed in rocks. We developed a theoretical auxetic 3D model consisting of rotating rigid bodies. To alleviate the mechanical assumption of rotating bodies, the theoretical model was modified to include crack-like features being represented by intersecting, elliptic cylinders. We then used a 3D printer to create a physical version of the modified model, whose PR was tested. We also numerically explored how the compressibility of fluids located in the pore-space of the modified model as well as how the elastic properties of the material from which the model is made of affect its auxetic behavior. We conclude that for a porous medium composed of a single material saturated with a single fluid (a) the more compliant the fluid is and (b) the lower the PR of the solid material, the lower the PR value of the composite material.

Fracture Behavior of Epoxy Resins in Fabric‐Supported Form

SummaryElastic‐plastic fracture behavior of a structural adhesive in the bulk and bonded forms is discussed. The model adhesive chosen with and without scrim carrier cloth (neat resin) solid film adhesives exhibit a relatively brittle material behavior to justify the use of Linear Elastic Fracture Mechanics (LEFM) methods. The solid film adhesives are first cast in the form of tensile coupons to determine the bulk fracture properties with the use of single‐edge‐cracked specimen geometry. KIC evaluation is done using the procedure suggested by the ASTM standard. A K‐calibration method based on application of boundary collocation procedure to the William's stress function is utilized to relate the measured critical loads to the KIC values. The yield stresses (σY) and elastic moduli (E) values in the bulk tensile mode are also evaluated. The availability of KIC, σY, E and ν (Poisson's ratio) values makes the calculation of crack tip plastic zone radii (rYC) and fracture energy (GIC) values possible on the basis of Irwin's theory. The bulk casting procedure is done under different cure (temperature, time and cool‐down) conditions to determine optimum properties. We found that the most suitable model that would fit the stress‐strain response of the model adhesives with prediction of the stress whitening stress level, σ*, under material damage surrounding flaws and crack tips was a modified version of Ramberg‐Osgood equation. A bilinear behavior is obtained when log(ϵp) is plotted against log(σ – Θ). The plastic strain ϵp is assumed to be a function of the over‐stress above the elastic limit stress, Θ, and the stress levels defining the intersection point for the bilinear behavior are found to occur slightly below the stress whitening stress values.