Adhesive Joint Model for Delamination Analysis of a Co-Cured Composite Joint: Applicability and Limitation

2019 ◽  
Vol 86 (5) ◽  
Author(s):  
C. N. Duong
Keyword(s):  
Adhesive Joint ◽  
Load Transfer ◽  
Strain Energy Release ◽  
Joint Model ◽  
Fe Analysis ◽  
Cohesive Elements ◽  
Composite Joint ◽  
Energy Release Rates ◽  
Material Forming ◽  
Joint Characteristic

Modeling the interface between two adherents in a co-cured composite joint for a delamination analysis is always a challenge since properties and thickness of the material forming the interface are not clearly defined or well characterized. In a conventional finite element (FE) analysis using virtual crack closure technique (VCCT) based on a linear elastic fracture mechanics (LEFM) theory, adherents are assigned to share the same common nodes along their intact interface. On the other hand, an FE analysis using cohesive elements or analytical methods based on an adhesive joint model for a delamination analysis of a co-cured joint will require modeling of the interface as well as the appropriate selection of its thickness and properties. The purpose of this paper is to establish the applicability and limitation of the adhesive joint model for a delamination analysis of a co-cured composite joint. In particular, it will show that when certain requirements are met, the strain energy release rates (SERR) become independent or nearly independent of the adhesive stiffness and thickness, and thus, SERR of an adhesive joint will be the same as that for a co-cured joint. These requirements are determined from a theoretical consideration, and they can be expressed explicitly in terms of joint characteristic (or load transfer) lengths and joint physical lengths. The established requirements are further validated by numerical results for various cracked joint geometries. Finally, implication of a mode ratio obtained by the proposed adhesive joint model for a corresponding delamination crack is discussed.

Three Stages of Fatigue Crack Growth in GFRP Composite Laminates

2000 ◽  
Vol 123 (1) ◽  
pp. 139-143 ◽  
Author(s):  
Jie Tong
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Energy Release ◽  
Crack Growth ◽  
Strain Energy ◽  
Strain Energy Release ◽  
Release Rates ◽  
Energy Release Rates ◽  
Three Stages ◽  
Strain Energy Release Rates

Multiple fatigue crack growth behavior has been studied in model transparent GFRP laminates. Detailed experimental observations have been made on the growth of individual fatigue cracks and on the evolution of cracks in off-axis layers in 0/90/±45S and ±45/90S laminates. Three stages of fatigue crack growth in the laminates have been identified: initiation, steady-state crack growth (SSCG), crack interaction and saturation. The results show that SSCG rate is essentially constant under constant load, independent of crack length and crack spacing. Finite element models have been developed and used to calculate the strain energy release rates associated with the off-axis matrix cracking. A correlation has been achieved between fatigue crack growth rates in off-axis layers and the total strain energy release rates.

A Preliminary Study on the Mechanical Performance of Tiled Polymer Composites

2006 ◽  
Author(s):  
M. A. Qidwai ◽  
J. N. Baucom ◽  
A. C. Leung ◽  
J. P. Thomas
Keyword(s):  
Composite Laminates ◽  
Load Transfer ◽  
Mechanical Performance ◽  
Local Stress ◽  
Superior Performance ◽  
Design Parameters ◽  
Interlaminar Stresses ◽  
Stress Concentrations ◽  
Critical Design ◽  
Composite Joint

We are developing and exploring the concept of in-plane tiling of composite laminates, called MOSAIC, to mitigate or control delamination at free edges due to interlaminar stresses. Initial mechanical testing has shown that MOSAIC composites with uniaxial graphite-fiber reinforced tiles retain the stiffness levels of traditional uniaxially reinforced composites but with reduced strength. The reduction in strength is attributed to the formation of resin-rich pockets between adjacent tiles. In this study, we have performed detailed finite element analyses to identify the critical design parameters that affect the mechanical performance of uniaxially reinforced MOSAIC composites. We have found that using continuous laminae on the outer surfaces significantly increases the overall loadcarrying capacity. Increasing aspect ratio of the pocket and decreasing material property differences between resin and tiles also cause better load transfer between tiles but may not necessarily improve overall strength due to increasing stress concentration. The tiling scheme and density of pocket placement influence the interaction of local stress concentrations. Consequently, a novel composite joint is proposed and found to have superior performance.

A Standard Approach for Measuring Adhesion Energies in Stiction-Failed Microdevices

2006 ◽  
Author(s):  
Zayd C. Leseman ◽  
Steven Carlson ◽  
Xiaojie Xue ◽  
Thomas J. Mackin
Keyword(s):  
Strain Energy ◽  
Peel Test ◽  
Strain Energy Release ◽  
Piezo Actuator ◽  
Release Rates ◽  
Linear Elastic ◽  
Macro Scale ◽  
Energy Release Rates ◽  
Elastic Fracture ◽  
Strain Energy Release Rates

We present results from a new procedure developed to quantify the pull-off force and strain energy release rates associated with stiction-failure in microdevices. The method is analogous to a standard, macro-scale peel test, but carried out using micro-scale devices. Adhesion is initiated by lowering an array of microcantilevers that protrude from a substrate into contact with a separate substrate. Displacement is controlled by a piezo-actuator with sub-nm resolution while alignment is controlled using linear and tilt stages. An interferometric microscope is used to align the array and the substrate and to record deflection profiles and adhesion lengths during peel-off. This geometry is accurately modeled using linear elastic fracture mechanics, creating a robust, reliable, standard method for measuring adhesion energies in stiction-failed microdevices.

Effects of Crimped Fiber Paths on Mixed Mode Delamination Behaviors in Woven Fabric Composites

2016 ◽  
Author(s):  
Paul V. Cavallaro ◽  
Andrew Hulton ◽  
Mahmoud Salama ◽  
Melvin W. Jee
Keyword(s):  
Fracture Toughness ◽  
Energy Release ◽  
Mixed Mode ◽  
Strain Energy ◽  
Strain Energy Release ◽  
Woven Fabric ◽  
Woven Fabric Composites ◽  
Fabric Composites ◽  
Energy Release Rates ◽  
Strain Energy Release Rates

This research investigated the fracture toughness and crack propagation behaviors of woven fabric reinforced polymer (WFRP) composite laminates subjected to single and mixed mode loadings using numerical models. The objectives were to characterize the fracture behaviors and toughness properties at the fiber/matrix interfaces and to identify mechanisms that can be exploited for increasing delamination resistance. The mode-I and mode-II strain energy release rates GI and GII, the effective critical strain energy release rate, Gc_eff, (also known as the mixed mode fracture toughness) and crack growth stabilities were determined as functions of crimped fiber paths using meso-scale, 2D multi-continuum finite element models. Three variations of a plain-woven fabric architecture were considered; each having different crimped fiber paths. The presence of mixed-mode strain energy release rates at the meso-scale due to the curvilinear fiber paths was shown to influence the interlaminar fracture toughness and was explored for pure single-mode and mixed-mode global loadings. It was concluded that woven fabric composites provided a Fracture Toughness Conversion Mechanism (FTCM) and their toughness properties were dependent upon and varied with positon along the crimped fiber paths. The FTCM was identified as an advanced tailoring mechanism that can be further utilized to improve toughness and damage tolerance thresholds especially when the mode-II fracture toughness GIIc is greater than the mode-I fracture toughness GIc.

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