Numerical analysis of the dual actuator load test applied to fracture characterization of bonded joints (original) (raw)
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Engineering Fracture Mechanics, 2013
The present work is dedicated to development of a crack equivalent data reduction scheme applied to the load jig previously developed by Fernlund and Spelt [1] in order to characterize fracture of bonded joints under mixed-mode I + II loading. The jig allows for easy alteration of the mode-mixity and permits covering the full range of mixed-mode I + II combinations. A data reduction scheme based on specimen compliance, beam theory and crack equivalent concept is proposed to overcome several difficulties inherent to the test analysis. The method assumes that the performed test can be viewed as a combination of the double cantilever beam and asymmetrically loaded end-notched flexure tests, which provide modes I and II fracture characterization, respectively. A numerical analysis including a cohesive mixed-mode I + II damage model was performed considering different mixed-mode loading conditions to validate the proposed data reduction scheme. Issues regarding self-similar crack growth and fracture process zone development are discussed. It was verified that the considered in-plane mix mode fracture criterion is well captured using the proposed data reduction scheme.
Design and Development of an Adhesive Joint Testing Apparatus for Mixed-Mode Evaluation
2013
The present work is dedicated to the development and design of a load jig inspired in the proposed solution by Fernlund and Spelt in order to characterize fracture of bonded joints under mixed-mode I+II loading. The jig allows for easy alteration of the mode-mixity and permits covering the full range of mixed-mode I+II combinations. A data reduction scheme based on specimen compliance, beam theory and crack equivalent concept is proposed to overcome several difficulties inherent to the test analysis. The development was based in a design methodology using numerical validation based on experimental data obtained with a Dual Loading Frame from Virginia Tech. This methodology is presented and then validated with the experimental application of the jig. INTRODUCTION Bonded joints are being increasingly applied in structures involving risk, as is the case of the aeronautical, automotive, and civil infrastructure industries. The classical strength prediction based on stress or strain anal...
An apparatus for mixed-mode fracture characterization of adhesive joints
Theoretical and Applied Fracture Mechanics, 2017
This paper describes a method of measuring the toughness of adhesive joints in various mixed mode combinations from mode I (opening) to mode II (shear) relying exclusively on the load-displacement curve obtained from an universal testing machine and the displacement from two linear variable differential transformers (LVDT) connected to the specimen beams. The novelty of the method reported here is that it does not use a visual crack length measurement, instead employing a method that deduces the crack length from the displacement obtained from LVDTs. Relying exclusively on the three machine outputs described, it allows for an automated data reduction scheme and, therefore, results in an easier analysis that is both accurate and not depending on human observation. Validation of the mixed-mode results was performed using classic mixed-mode tests and classic pure-mode tests which provided comparable results, therefore validating the apparatus results.
Mixed mode fracture testing of adhesively bonded wood specimens using a dual actuator load frame
Holzforschung, 2010
An experimental evaluation of mixed mode fracture tests conducted on adhesively bonded wood specimens using a dual actuator load frame is presented. This unit allows the fracture mode mixity to be easily varied during testing of a given specimen, providing improved consistency, accuracy, and ease of testing over a range of loading modes. Double cantilever beam (DCB) type specimens made of southern yellow pine (Pinusspp.) wood substrates bonded with a commercially available one part polyurethane adhesive were tested over a wide range of mode mixities from pure mode I to pure mode II. The critical strain energy release rate (SERR) values were calculated from the measured load, displacement, and crack length data, in combination with material properties and specimen geometric parameters, and compared on aversusfracture envelope plot. Mean quasi-static fracture energy values were calculated to be 390 J m-2and 420 J m-2for mode I and mode II fracture, respectively. For various mixed mode...
International Journal of Fracture, 2007
ABSTRACT Characterizing the fracture energy of bonded adhesive joints over a range of mode mixities often requires special fixtures or a variety of test configurations. By pairing a tapered and a constant thickness adherend, a hybrid double cantilever beam (DCB) specimen is proposed. This asymmetric tapered DCB configuration can be used to determine the fracture energy as a function of mode mixity. As the debond propagates, the relative stiffness of the adherends varies in a systematic manner, resulting in a range of mode mixities from 0° to approximately 20°. Strain energy release rates were obtained using corrected beam theory and a finite element fracture analysis. Single-leg bending tests were used to determine the fracture energy at mode mixity up to 56°. Constant thickness and tapered DCB tests were used to determine the mode I fracture energy. The resulting fracture envelope was constructed in order to show the dependence of the fracture energy on mode mixity for a two part acrylic adhesive.
Journal of Adhesion Science and Technology, 2009
In contrast to fracture in monolithic materials, where cracks naturally grow in a mode I manner, fracture in laminated or adhesively bonded joints often involves cracks growing under mixed mode conditions. In many cases, the mixed mode fracture energy increases as the fracture mode changes from mode I to mode II, but exceptions have been noted for several practical engineering adhesives. In some cases, G IIc may be less than G Ic , while in other situations, failure may occur at total energy release rate (G T = G I + G II) values that are smaller than either of the pure mode fracture energies. Several examples of this behavior are reported along with possible explanations for the behavior, which often involves the propagation of the growing debond into regions where less energy is dissipated by the fracture process. These examples showing that mixed mode fracture energies of adhesive joints may be lower than pure mode fracture energies remind us of the importance of developing fracture envelopes over a wide range of mode mixities for engineering design.
Mixed-Mode I + II Fracture Characterization of Bonded Joints using a Novel Multi-Mode Apparatus
2013
Este trabajo esta dedicado a la elaboracion y diseno de un aparato inspirado en la solucionpropuesta por Fernlund y Spelt para caracterizar la fractura de las uniones adhesivas bajoaplicaciones de cargas en modo mixto I + II . El aparato permite una facil variacion delmodo de mezcla y cubre todo el rango de combinaciones posibles (I y II).Ademas, se propone un procedimiento para tratamiento de datos en funcion del tamano degrieta, basado en la teoria de la viga y el concepto de grieta equivalente, superando variasdificultades inherentes a los ensayos realizados. El desarrollo se basa en una metodologiade diseno mediante la validacion numerica basada en datos experimentales obtenidos conun equipo de ensayo de doble accion en Virginia Tech. Esta metodologia se presenta acontinuacion, y esta validada con la aplicacion experimental del aparato.
THE JOURNAL OF ADHESION, 2019
The dissemination of composite materials introduces applications of hybrid structures with composite and metal parts. The development of reliable methodologies to evaluate the performance of these structures is required. In this work, the mixed-mode fracture behaviour of a bi-material adhesively bonded joint is investigated. A new strain-based criterion for the design of the mixed-mode bending (MMB) bi-material specimen is suggested. A new analytical partitioning method based on the ‘global method’ is proposed and tested on a composite-to-metal bonded joint and compared with a finite element model using the virtual crack closure technique (VCCT). The results show that the proposed strain-based design methodology can be successfully used in MMB test for bi-material joints. The fracture mode partitioning is accurately predicted by the analytical method. However, the absolute values of the strain energy release rate (SERR) predicted by the analytical method are only accurate if the shear deformation in the test is not significant.
Analysis of the mixed-mode end load split delamination test
Composite Structures, 2006
Composite delaminations are commonly characterized using the double cantilever beam test for mode I, the end-notched flexure test or the end load split test for mode II and the mixed-mode bending test for mixed-mode. For all these tests, the mode mix remains constant and does not vary with the crack length. However, in the mixed-mode end load split test (MMELS), the delamination propagates under a varying mode mix that depends on the crack extension, which is a more realistic scenario. The MMELS test has been previously analysed by different researchers but the resulting expressions are not equivalent. A more accurate alternative analysis of the test, based on the finite element method and the virtual crack closure technique, is used in the present work for comparison. The results are compared to the predictions of approaches presented in the literature and significant findings are found for materials characterization using the MMELS test.