In-plane Tensile Loading Research Articles

Evaluation of нот cracking susceptibility of nickel-based alloys during welding with forced deformation

Nickel alloys are widely used in the nuclear power industry, turbine construction, chemical engineering. The alloys have high mechanical properties, corrosion resistance, but they are prone to the hot cracking in welding. One of such alloys is Inconel 690. The aim of the article is to estimate the hot cracking susceptibility of Inconel 690 alloy in welding. The hot cracking resistance of the joint was determined according to the Varestraint-test method (longitudinal extension), the Transvarestraint-test method (lateral extension) and the PVR-test method (the in-plane tensile load acting along the weld with a programmable rate of deformation). The welding of the samples was performed by the nonconsumable electrode in the inert gas without additives (TIG) and by the multilayer cladding with the Inconel 52 wire, respectively. The criteria for evaluation of the hot cracking resistance according the first two methods were the total crack length as well as the maximum crack length or the temperature range of brittleness. The criterion of hot cracking susceptibility at the PVR-test was the critical strain rate at which the first cracks appear. The selected test methods allow one to set quantitative and qualitative assessment of the tendency against crystallization and undersolidus cracks. It is stated that the welds formed with the Inconel 52 wire are more susceptible to crack formation of holes of plasticity (undersolidus cracks (Vcr = 3 mm / min) than to the formation of crystallization cracks (Vcr = 9 mm / min)). The temperature range of the plasticity cracking holes is 1150 ... 600 0 С. The destruction occurs on the big angle grain boundaries.

Fully-Modeled Unit Cell Analysis for Macro/Micro Elastic-Viscoplastic Behavior of Quasi-Isotropic CFRP Laminates

A fully-modeled unit cell analysis is performed to investigate the macroscopic and microscopic elastic-viscoplastic behaviors of a quasi-isotropic carbon fiber-reinforced plastic (CFRP) laminate. To this end, a quasi-isotropic CFRP laminate and its microstructure composed of carbon fibers and a matrix material are considered three-dimensionally. Then, a hexagonal prism-shaped unit cell fully modeled with fibers and a matrix including interlaminar areas is defined. For this quasi-isotropic laminate, a homogenization theory for nonlinear time-dependent composites with point-symmetric internal structures is applied, enabling us to analyze both the macroscopic and microscopic elastic-viscoplastic behaviors of the laminate. The substructure method is introduced into the theory to reduce computational costs. The present method is then applied to the elastic-viscoplastic analysis of a quasi-isotropic carbon fiber/epoxy laminate subjected to an in-plane uniaxial tensile load, to investigate the macroscopic elastic-viscoplastic behavior of the laminate and the microscopic stress and strain distributions in them.

Size dependent response of large shell elements under in-plane tensile loading

Large-scale thin-walled structures with a low weight-to-stiffness ratio provide the means for cost and energy efficiency in structural design. However, the design of such structures for crash and impact resistance requires reliable FE simulations. Large shell elements are used in those simulations. Simulations require the knowledge of the true stress–strain response of the material until fracture initiation. Because of the size effects, local material relation determined with experiments is not applicable to large shell elements. Therefore, a numerical method is outlined to determine the effect of element size on the macroscopic response of large structural shell elements until fracture initiation. Macroscopic response is determined by introducing averaging unit into the numerical model over which volume averaged equivalent stress and plastic strain are evaluated. Three different stress states are considered in this investigation: uniaxial, plane strain and equi-biaxial tension. The results demonstrate that fracture strain is highly sensitive to size effects in uniaxial tension whereas in plane strain or equi-biaxial tension size effects are much weaker. In uniaxial and plane strain tension the fracture strain for large shell elements approaches the Swift diffuse necking condition.

Two-dimensional non-linear finite element analysis of CMC microstructures

A research program has been developed to quantify the effects of the microstructure of a woven ceramic matrix composite and its variability on the effective properties and response of the material. In order to characterize and quantify the variations in the microstructure of a five harness satin weave, chemical vapor infiltrated (CVI) SiC/SiC composite material, specimens were serially sectioned and polished to capture images that detailed the fiber tows, matrix, and porosity. Open source quantitative image analysis tools were then used to isolate the constituents, from which two dimensional finite element models were generated which approximated the actual specimen section geometry. A simplified elastic–plastic model, wherein all stress above yield is redistributed to lower stress regions, is used to approximate the progressive damage behavior for each of the composite constituents. Finite element analyses under in-plane tensile loading were performed to examine how the variability in the local microstructure affected the macroscopic stress–strain response of the material as well as the local initiation and progression of damage. The macroscopic stress–strain response appeared to be minimally affected by the variation in local microstructure, but the locations where damage initiated and propagated appeared to be linked to specific aspects of the local microstructure.

Stochastic First-Ply Failure Analysis of Laminated Composite Plates under in Plane Tensile Loading

The present work deals with second order statistics of first-ply failure response of geometrically nonlinear laminated composite plate subjected to in-plane tensile loading with random system properties. System properties such as the material properties and lamina plate thickness are modeled as independent random variables.The mathematical formulation is based on higher order shear deformation theory (HSDT) with von-Karman nonlinear kinematics. An efficient C0 nonlinear finite element method based on direct iterative procedure in conjunction with a first order perturbation approach (FOPT) is extended successfully and applied for failure problem in random environment and is employed to evaluate the dimensionless mean failure load and variance of failure index by modeling the system properties as basic random variables using Tsai-Wu and Hoffman failure criteria.Typical numerical results are presented to examine the effect of amplitude ratios, boundary conditions, lamination schemes with random system properties for different failure criterion.The results obtained using present solution approach is validated with the results available in the literatures.

Failure strain and stress fields of a chopped glass-reinforced polyester under biaxial loading

We perform experimental tests to obtain biaxial stress states in a chopped glass-reinforced polyester composite, applying in-plane perpendicular tensile loads to cruciform specimens. Three different specimens’ geometries have been considered for obtaining adequate failure modes with different loading cases. The scope is to estimate the strain and the stress failure states by measuring with gages the strains developed in the central zone, where a plane stress state with zero shear component occurs. We develop numerical simulations using the Finite Element Method in order to achieve a better understanding of the behaviour of the cruciform specimens under loading and to compare the numerical results with the experimental data. Maximum stress, Maximum strain, Tsai-Hill and Tsai-Wu biaxial failure theories are evaluated for the assumption of isotropic behaviour and contrasted with the experimental results.

Quasi-static tensile behavior and damage of carbon/epoxy composite reinforced with 3D non-crimp orthogonal woven fabric

This paper presents a comprehensive experimental study and detailed mechanistic interpretations of the tensile behavior of one representative 3D non-crimp orthogonal woven (3DNCOW) carbon/epoxy composite. The composite is tested under uniaxial in-plane tensile loading in the warp, fill and ±45° bias directions. An “S-shape” nonlinearity observed in the stress–strain curves is explained by the concurrent contributions of inherent carbon fiber stiffening (“non-Hookean behavior”), fiber straightening, and gradual damage accumulation. Several approaches to the determination of a single-value Young’s modulus from a significantly nonlinear stress–strain curve are discussed and the best approach recommended. Also, issues related to the experimental determination of effective Poisson’s ratios for this class of composites are discussed, and their possible resolution suggested. The observed experimental values of the warp- and fill-directional tensile strengths are much higher than those typically obtained for 3D interlock weave carbon/epoxy composites while the nonlinear material behavior observed for the ±45°-directional tensile loading is in a qualitative agreement with the earlier results for other textile composites. Results of the damage initiation and progression, monitoried by means of acoustic emission, full-field strain optical measurements, X-rays and optical microscopy, are illustrated and discussed in detail. The damage modes at different stages of the increasing tensile loading are analyzed, and the principal progressive damage mechanisms identified, including the characteristic crack patterns developed at each damage stage. It is concluded that significant damage initiation of the present material occurs in the same strain range as in traditional cross-ply laminates, while respective strain range for other previously studied carbon/epoxy textile composites is significantly lower. Overall the revealed advantages in stiffness, strength and progressive damage behavior of the studied composite are mainly attributed to the absence of crimp and only minimal fiber waviness in the reinforcing 3DNCOW preform.

A structural modelling framework for prediction of damage development and failure of composite laminates

This article presents the latest developments of a constitutive modelling framework, CODAM (COmposite DAmage Model), for predicting the non-linear in-plane response of composite laminates using continuum damage mechanics. The methodology is best suited for non-linear structural analysis of large-scale laminated composites whose boundaries do not interfere/interact with the damage zone that develops and grows within the structure. The new development presented here, CODAM2, addresses the deficiencies in both the numerical and material objectivity of the original version of CODAM. While the previous CODAM formulation was essentially a local smeared crack model that was augmented with crack band scaling to overcome one aspect of the numerical objectivity, namely the mesh-sensitivity, CODAM2 introduces a non-local regularisation scheme to alleviate both the spurious mesh dependency and mesh orientation problems that plague all local strain-softening models. Two of the 13 test cases, provided in the third-world wide failure exercise, which were related to the in-plane tensile and compressive loading of open hole specimens, were used in order to demonstrate the effectiveness of CODAM2 in predicting the damage development and the corresponding overall response in such structural loading configurations.

Free Edge Stress Analysis of Unidirectional CFRP Laminates Based on a Homogenization Theory for Time-Dependent Composites

In this study, distributions of microscopic stress at free edges of unidirectional carbon fiber-reinforced plastic laminates (CFRP laminates) are analyzed three-dimensionally, based on a homogenization theory for time-dependent composites. For this, the homogenization theory is reconstructed for free edge problems using a traction-free boundary condition. Then, an analysis domain is reduced using the point-symmetry of the internal structure of the unidirectional CFRP laminate. Moreover, the substructure method is newly introduced into the theory to reduce the computational costs required for the analysis. The present method is then applied to the elastic-viscoplastic microscopic stress analysis at free edges of unidirectional carbon fiber/epoxy laminates subjected to an in-plane uniaxial tensile load. It is shown that complex microscopic stress distributions occur in the vicinity of the free edge, especially around fiber/matrix interface regions.

Refined fixture design for effective essential work of fracture toughness characterization of m-LLDPE thin films

Characterization of Mode-I fracture toughness of ductile polymeric thin films is nontrivial. Proper specimen preparation and experimental procedures are required to ensure in-plane tensile loading. In this study, a custom-built double-edge notched tensile test fixture was employed to characterize the Mode-I essential work of fracture (EWF) toughness of metallocene linear low-density polyethylene (m-LLDPE) films. Effects of specimen geometry, strain rate and film orientation on the specific essential work of fracture, we, and the specific non-essential work of fracture, wp, were investigated. Results indicate both EWF parameters are independent of the crosshead speed, gauge length (distance between upper and lower clamps) and specimen width within the ranges tested. we is significantly higher for thinner films and for crack propagation perpendicular to the blown film machine direction (MD). The usefulness of EWF for evaluating m-LLDPE fracture toughness is discussed.

Analysis of an adhesively bonded single lap joint subjected to eccentric loading

A new experimental test is proposed, which allows the contribution of Mode I, II and III fracture modes to the failure of the adhesive layer of bonded joints aiming at achieving the realistic conditions often occurring during loading of practical joints. The main objective of this test is benchmarking of computational tools. The test is based on a Single Lap Joint subjected to Eccentric Loading (SLJ-EL). The basic concept that lies behind this configuration is that the applied in-plane tensile load leads the adhesive layer to develop normal stresses, in-plane and out-of-plane shear stresses, which correspond to Mode I, II and III loading and fracture. These tests were designed so that the metal substrates do not enter plasticity and the adhesive achieves a mode mixity ratio between Mode II and Mode III not lower than 0.5. The experiments were simulated in a 3-dimensional finite element space and a previously developed mixed-mode model is utilized for the adhesive layer, under the framework of Cohesive Zone Modeling (CZM) techniques. The numerical results are in very good agreement with the corresponding experimental measurements, as regards both the linear and non-linear region, and the attained strength. It is concluded that in the early stages of loading the contribution of Mode III is 150% higher than that of Mode II.

A combined elastoplastic damage model for progressive failure analysis of composite materials and structures

The paper is concerned with the development and verification of a combined elastoplastic damage model for the progressive failure analysis of composite materials and structures. The model accounts for the irreversible strains caused by plasticity effects and material properties degradation due to the damage initiation and development. The strain-driven implicit integration procedure is developed using equations of continuum damage mechanics, plasticity theory and includes the return mapping algorithm. A tangent operator consistent with the integration procedure is derived to ensure a computational efficiency of the Newton–Raphson method in the finite element analysis. The algorithm is implemented in Abaqus as a user-defined subroutine. The efficiency of the constitutive model and computational procedure is demonstrated using the analysis of the progressive failure of composite laminates containing through holes and subjected to in-plane uniaxial tensile loading. It has been shown that the predicted results agree well with the experimental data reported in the literature.

Effect of woven fabric architecture on interlaminar mechanical response of composite materials: an experimental study

Woven fabrics are usually selected for the reinforcement phase in laminated composite materials due to their balanced in-plane mechanical and thermal properties and their relatively simple handling during the composite fabrication process. One of the questions that usually arise in the design of laminated composites is the selection of the woven fabric architecture. It is well known the effect that this architecture plays in the in-plane elastic and ultimate composite properties under either in-plane tensile or shear loading. However, the effect of the woven fabric architecture on the mechanical response of composites under interlaminar shear loading is not well established. An experimental study was conducted to determine the role of the woven fabric architecture and its geometrical parameters on the interlaminar shear response of laminated composites. A set of composite materials with the same epoxy matrix and carbon fiber were prepared with five different woven fabrics of similar areal density and fiber volume fraction. The experimental results reveal that the interlaminar shear modulus is not significantly affected by the woven fabric architecture and that the interlaminar shear strength is not only dependent on the amount of crimp in the woven fabric reinforcement but also significantly affected by bridging effects.

Analysis of Nonlinear Shear Deformations in CFRP and GFRP Textile Laminates

Carbon fibre-reinforced polymer (CFRP) and glass fibre-reinforced polymer (GFRP) woven composites are widely used in aerospace, automotive and construction components and structures thanks to their lower production costs, higher delamination and impact strengths. They can also be used in various products in sports industry. These products are exposed to different in-service conditions such as large tensile and bending deformations. Composite materials, especially ±45° symmetric laminates subjected to tensile loads, exhibit significant material as well as geometric non-linearity before damage initiation, particularly with respect to shear deformations. Such a nonlinear response needs adequate means of analysis and investigation, the major tools being experimental tests and numerical simulations. This research deals with modelling the nonlinear deformation behaviour of CFRP and GFRP woven laminates subjected to in-plane tensile loads. The mechanical behaviour of woven laminates is modelled using nonlinear elasto-plastic as well as material models for fabrics in commercial finite-element code Abaqus. A series of tensile tests is carried out to obtain an in-plane full-field strain response of [+45/-45]2s CFRP and GFRP laminates using digital image correlation technique according to ASTM D3518/D3518M-94. The obtained results of simulations are in good agreement with experimental data.

Performance of bolted joints in Discontinuous Ceramic Cored Sandwich Structures – Static experimental testing

Thick section composites that consist of discontinuous ceramic tile arrays as a core represent a unique class of sandwich structures. They have been developed to provide a balance of structural, impact, and penetration resistance at minimum weight. Bolted joints are often used to fasten the Discontinuous Ceramic Cored Sandwich Structures (DCCSS) to other structures. Extensive experimental testing has been completed in order to better understand the performance of bolted joints in DCCSS. In this study, pin-loaded specimens are subjected to static in-plane tensile loading to establish the sequence and severity of failure modes and ultimate joint capacity. Static testing was completed on various geometric ratios such as edge distance effects, as well as the influence of tile gaps that exist in the discontinuous tile array. The results from this study establish guidelines for design of bolted joints in DCCSS.

Analytical and experimental studies on the low-velocity impact response and damage of composite laminates under in-plane loads with structural damping effects

In this paper, low-velocity impact response and damage of composite laminates under in-plane loads are analytically and experimentally investigated. The authors recently proposed a modified displacement field of plate theory, considering the effect of initially loaded in-plane strain, and used a finite element program to analyze the structural behavior of the composite laminate. In this study, the program is upgraded to account for the structural damping effect of the laminate. A pendulum type impact test system and an in-plane loading fixture are constructed for the experimental study. The analytical and experimental impact behaviors are compared at different impact energy levels for cases with an initial in-plane tensile load and a compressive load, as well as cases without the initial in-plane load. The results show good correspondence between the analytical and experimental impact force histories. The effect of the initial in-plane load reduces for higher impact energies. The numerical estimation of the damaged area is in good agreement with the results from C-scanning experiments.

Three-Phase Textile Nanocomposites: Significant Improvements in Strength, Toughness and Ductility

It is well established that in-plane tensile properties of unidirectional microfiber-reinforced composites are not significantly influenced by addition of carbon nanotubes to the matrix. This is because the principal effect of the nanotubes is to enhance the matrix dominated (out-of-plane) properties. Here we report that the above situation changes when nanotubes are incorporated into woven-fabric (textile) composites. We report up to 200% increase in strain-to-break and 180% increase in toughness under in-plane tensile load with approximately 0.05% weight of nanotube additives. We attribute this effect to the geometrical arrangement of the micro-fibers and the critical role of the pure-matrix-block in textile composites.

Characterization of In-Plane Mechanical Properties of Laminated Hybrid Composites

An experimental investigation was conducted to study the effect of hybrid composite specimen subjected to in-plane tensile and compressive loading. The laminated specimens in accordance with ASTM standards were fabricated using steel and nylon bi-directional mesh as reinforcements and polyester as the binder. The various volume fractions and fiber orientations were used in which the percentage of polyester (40%) was maintained constant. From the investigations it is revealed that, the specimens with higher percentage of steel sustain greater loads & also the strengths are superior in case of 0/900 oriented specimens. A relationship between the tensile/compressive strength, fiber content and orientation has been established.

Nonlinear elastic behavior of graphene:Ab initiocalculations to continuum description

The nonlinear in-plane elastic properties of graphene are calculated using density-functional theory. A thermodynamically rigorous continuum description of the elastic response is formulated by expanding the elastic strain energy density in a Taylor series in strain truncated after the fifth-order term. Upon accounting for the symmetries of graphene, a total of fourteen nonzero independent elastic constants are determined by least-squares fit to the ab initio calculations. The nonlinear continuum description is valid for infinitesimal and finite strains under arbitrary in-plane tensile loading in circumstance for which the bending stiffness can be neglected. The continuum formulation is suitable for incorporation into the finite element method.

A comparative study of tensile properties of non-crimp 3D orthogonal weave and multi-layer plain weave E-glass composites. Part 2: Comprehensive experimental results

This Part 2 paper presents results of comparative experimental study of progressive damage in 2D and 3D woven glass/epoxy composites under in-plane tensile loading. As Part 1, this Part 2 work is focused on the comparison of in-plane tensile properties of two non-crimp single-ply 3D orthogonal weave E-glass fibre composites on one side and a laminate reinforced with four plies of E-glass plain weave on the other. The damage investigation methodology combines mechanical testing with acoustic emission registration (that provides damage initiation thresholds), progressive cracks observation on transparent samples, full-field surface strain mapping and cracks observation on micrographs, altogether enabling for a thorough characterisation of the local micro- and meso-damage modes of the studied composites. The obtained results demonstrate that the non-crimp 3D orthogonal woven composites have significantly higher in-plane strengths, failure strains and damage initiation thresholds than their 2D woven laminated counterpart. The growth of transverse cracks in the yarns of 3D composites is delayed, and they are less prone to a yarn–matrix interfacial crack formation and propagation. Delaminations developing between the plies of plain weave fabric in the laminate at certain load level never appear in the 3D woven single-ply composites.