Vibration analysis of delaminated composite beams and plates using a higher-order finite element

: Static strength methodology and evaluations of joint static and fatigue test data are reported. Analytic studies complement methodology development and illustrate: the need for detailed stress analysis, the utility of the developed 'Bolted Joint Stress Field Model' (BJSFM) procedure, and define model limitations. For static strength data, correlations with analytic predictions are included. Data trends in all cases are discussed relative to joint strength and failure mode. For joint fatigue studies, data trends are discussed relative to life, hole elongation, and failure mode behavior.

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Effect of Variances and Manufacturing Tolerances on the Design Strength and Life of Mechanically Fastened Composite Joints. Volume 3. Bolted Joint Stress Field Model (BJSFM) Computer Program User's Manual

: The objective of this program is development of failure criterion and improved fatigue life prediction methodology of mechanically fastened joints in advanced composite structure. This report summarizes activity for the period 15 February 1978 to 30 June 1978. Program activities are divided into five tasks: Task 1 - Literature Survey; Task 2 - Evaluation of Joint Design Variables; Task 3 - Evaluation of Manufacturing and Service Anomalies; Task 4 - Evaluation of the Effect of Critical Joint Design Parameters on Fatigue Life; Task 5 - Development of Final Analyses and Correlation. This report documents Task 1 - Literature Survey activities. Summarized are the state-of-the-art in design and analysis of mechanically fastened composite joints, selected methodology, conclusions, and recommendations for the remainder of this program.

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Effect of Variances and Manufacturing Tolerances on the Design Strength and Life of Mechanically Fastened Composite Joints

Theoretical modeling of fatigue phenomenon in composite pipes

Results from approximate and exact stress analyses are reported for elastic stress and displacement fields in two interlaminar mode II fracture toughness specimens. End-notched flexure tests for laminates and unidirectional composites are studied in detail. Based on approximate closed form solutions for energy release rates procedures are suggested for fitting compliance versus delamination length data. Such procedures should be followed when through the thickness shear moduli of the layers are small as compared to axial moduli.

Analysis of Test Specimens for Interlaminar Mode II Fracture Toughness, Part 1. Elastic Laminates:

The analytical and experimental study performed to expand the existing static and fatigue failure analysis is described. The analytical effort extended the analysis to include interlaminar effects, while the experimental effort developed methods to obtain basic experimental data required as input to the analysis. The static failure analysis for notched laminates was modified to include interlaminar effects near the notch. Three dimensional elastic and two dimensional elasticplastic finite element analysis were performed for some notched laminates.

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Evaluation and expansion of an analytical model for fatigue of notched composite laminates

: Typical flaws are identified and static analyses developed or presented to predict their growth. A 'wearout' fatigue concept is incorporated into the static/fatigue model and the concept of an instability boundary established for every flaw size and location. An experimental program is outlined to support the analysis and to measure the specific adhesive surface fracture energy quantitatively. Acoustic monitoring of the specimens to detect damage growth and a corresponding vibration analysis are carried out as a potential NDT and for correlation studies. Ultrasonic 'C' scans are used to ensure quality control and to determine approximate damage growth rates. The analytical and experimental results are incorporated into an NDE technique to quantitatively determine a measure of the residual lifetime and strength of the structural component. A comparison of these with a quantified criterion for damage tolerance would establish flaw criticality through the need, or lack of it, for mandatory repair.

S. V. Kulkarni

Papers

Evaluation and expansion of an analytical model for fatigue of notched composite laminates

Definition and Modeling of Critical Flaws in Graphite Fiber Reinforced Epoxy Resin Matrix Composite Materials.

Analytical Modeling and ND Monitoring of Interlaminar Defects in Fiber-Reinforced Composites