M.J. Hinton

Lamina properties, lay-up configurations and loading conditions for a range of fibre-reinforced composite laminates

This paper gives details of the input data and a description of the laminates provided to all participants in an exercise to predict the strength of composite laminates. The input data include the elastic constants and the stress/strain curves for four unidirectional laminae and their constituents. Six types of laminates, chosen for the analysis, are described together with the lay-up, layer thicknesses, stacking sequences and the loading conditions. Consideration is given as to why these six laminates were selected and of the challenges imposed by the selected problems. The detailed instructions issued to the contributors are also presented.

A COMPARISON OF THE PREDICTIVE CAPABILITIES OF CURRENT FAILURE THEORIES FOR COMPOSITE LAMINATES

Abstract This paper presents a unique and comprehensive comparison between the predictions of internationally recognised failure theories for fibre-reinforced polymer-composite laminates. The theories were applied by their originators (or their colleagues) to carefully selected test cases covering a wide range of lay-ups, materials and in-plane loading conditions. Key features in each theory are identified including: types of failure models employed, whether linear or non-linear analysis was carried out, reliance on software and numerical methods, allowance for thermal stresses and identification of modes of failure. The results (initial and final failure envelopes and representative stress/strain curves) have been superimposed to show similarities and differences between the predictions of the various theories. In addition, bar charts were constructed to demonstrate the levels of agreement between the predicted initial and final failure stresses and strains. Sources of discrepancies between the predictions of the various failure theories are discussed. The originators have the opportunity to comment on and compare their theoretical predictions with experimental results in the second part of this Exercise which will be published separately.

A comparison of the predictive capabilities of current failure theories for composite laminates, judged against experimental evidence

Abstract This paper draws together the results from a co-ordinated study, known as the World-Wide Failure Exercise, whereby 12 of the leading theories for predicting failure in composite laminates have been tested against experimental evidence. The comparison has been effected through 14 carefully selected test cases, which include biaxial strength envelopes for a range of unidirectional and multi-directional laminates, and stress–strain curves for a range of multi-directional laminates, loaded under uniaxial or biaxial conditions. The predictions were provided by the originators of the theories, not by third parties, and were made without access to the experimental results beforehand. The predictions and experimental data have been compared in a systematic and detailed manner, to identify the strengths and weaknesses of each theory, together with a ranking of the overall effectiveness of each theory. Careful reading of this analysis and study of the figures provided will inform the reader when selecting an appropriate failure theory for use in a given design situation. It will also provide a qualitative assessment of the likely accuracy and reliability of the prediction in a given circumstance.

PREDICTING FAILURE IN COMPOSITE LAMINATES: THE BACKGROUND TO THE EXERCISE

Abstract This Special Edition of Composites Science and Technology is dedicated to the subject of failure theories for continuous fibre-reinforced-polymer composite materials (FRPs). The papers were commissioned as a co-ordinated study (referred to as the ‘failure exercise’) aimed at providing a comprehensive description of the foremost failure theories available at the present time, a comparison of their predictive capabilities directly with each other, and a comparison of their predictive capabilities against experimental data. This introductory paper sets the scene for the ‘failure exercise’, describing the process by which the participants were selected, the general instructions supplied to each participant and the format for presenting the output of the work.

Recommendations for designers and researchers resulting from the world-wide failure exercise

The World-Wide Failure Exercise (WWFE) contained a detailed assessment of 19 theoretical approaches for predicting the deformation and failure response of polymer composite laminates when subjected to complex states of stress. The leading five theories are explored in greater detail to demonstrate their strengths and weaknesses in predicting various types of structural failure. Recommendations are then derived, as to how the theories can be best utilised to provide safe and economic predictions in a wide range of engineering design applications. Further guidance is provided for designers on the level of confidence and bounds of applicability of the current theories. The need for careful interpretation of initial failure predictions is emphasised, as is the need to allow for multiple sources of non-linearity (including progressive damage) where accuracy is sought for certain classes of large deformation and final failure strength predictions. Aspects requiring further experimental and theoretical investigation are identified. Direction is also provided to the research community by highlighting specific, tightly focussed, experimental and theoretical studies that, if carried out in the very near future, would pay great dividends from the designers perspective, by increasing their confidence in the theoretical foundations.

Biaxial test results for strength and deformation of a range of E-glass and carbon fibre reinforced composite laminates: Failure exercise benchmark data

Abstract In Part A of the World Wide Failure Exercise (published in Composite Science and Technology , Vol 58, No 7, 1998), all contributors were given exactly the same set of material properties and were asked to predict the strength and deformation of the same set of laminates under a range of specified loading conditions. In this part (Part B) of the exercise, available experimental results are superimposed on the theoretical predictions and returned to the contributors for comment. The test data were for (a) 0° unidirectional laminae under biaxial direct and shear loads (b) (90°/±30°) s , (0°/±45°/90°) s , (±55°) s multi-directional laminates under biaxial loads and (c) stress strain curves for (0°/±45°/90°) s , (±55°) s , (±45°) s and (0°/90°) s laminates under uniaxial and biaxial loads. This paper briefly describes the experimental results issued in Part B of the Exercise and their origin and limitations. Comments are made on the material properties given for the unidirectional fibre reinforced layers and constituents used in Part A of the Exercise and on approximations in the laminate models specified in Part A.

A further assessment of the predictive capabilities of current failure theories for composite laminates: comparison with experimental evidence

Abstract This paper presents supplementary conclusions from an international exercise to establish the current status of failure prediction theories for polymer composite laminates. In previous stages of the exercise leading theoreticians in the field used 15 different approaches to predict a range of biaxial failure envelopes and stress–strain curves for composite laminates. The theoretical predictions were compared with experimental results and their performance was assessed using a process designed by the organisers Hinton, Soden and Kaddour [Compos Sci Technol 62 (2002) 1725]. During the course of the exercise four additional theories have emerged that add to the overall picture. The performance of the new theories is assessed here and compared with that of the other fifteen theories, using an identical methodology. The theories are ranked according to their abilities to predict the experimental results for failure of a unidirectional fibre reinforced lamina, initial and final failure of multi-directional laminates and large deformation of laminates under biaxial loads. An attempt is made to identify the most accurate approaches for use in a wide range of applications. The predictions of the four most highly ranked theories, which included two of the new approaches, were within ±50% (i.e. a factor of 2) of the experimental results in more than 75% of the test cases.

A comparison of the predictive capabilities of current failure theories for composite laminates: additional contributions

Abstract Following the publication of an article by Soden, Hinton and Kaddour (Compos Sci Technol, V58, pp. 1225–54, 1998), which compared the predictions of 14 internationally recognised failure theories for fibre reinforced polymer composite laminates, the present paper extends that comparative study to include five more theories, supplied by their originators. Evaluation of the predictive capabilities of the additional theories was carried out in an identical manner to the original study. The same test cases were utilised, covering a wide range of lay-ups, materials and in-plane loading conditions. The results (initial and final failure envelopes and representative stress–strain curves) have been superimposed to show similarities and differences between the predictions of the 19 theories. Final failure predictions for the additional theories fall within the existing range obtained from the original 14 theories but the initial failure predictions for the additional theories have widened the previously observed range. Comments are provided on the possible reasons for the increased spread.

Evaluation of failure prediction in composite laminates: background to ‘part B’ of the exercise

Abstract Over the past 10 years, an international study has been underway to determine the accuracy of current theories for predicting failure in polymer composite laminates. The study, known as the World-Wide Failure Exercise (WWFE), has been carried out in three distinct stages (referred to as Part A, Part B and Part C). Two previous special editions of the Composites Science and Technology journal were dedicated to the first two stages. Part A (Vol. 58, No. 7, 1998) contained detailed descriptions of 14 leading failure theories and predictions by each for a set of test cases defined by the organisers of the exercise (the authors of this paper). Part B (Vol. 62, Nos. 12–13, 2002) provided a detailed comparison between the theoretical predictions and the experimental results, in order to assess the level of maturity of the theories. Part C is aimed at serving a number of purposes. It extends the breadth of the study by including four additional theories that have emerged since the WWFE was first initiated. It provides a comprehensive view on the perceived strengths and weaknesses of all of the leading failure theories considered. It provides direction to designers on choice of theory and likely confidence in the prediction. It provides recommendations to the composites research community as to where efforts should be focussed to develop improved failure prediction tools. This introductory paper to the third special edition contains a detailed description of the process adopted for carrying out ‘Part C’, so that the composites community can draw appropriate conclusions on the overall probity (and hence reliability) of the study.

Input data for test cases used in benchmarking triaxial failure theories of composites

This article gives details of the input data provided for use in the Second World-Wide Failure Exercise (WWFE-II) for benchmarking triaxial failure criteria. It includes (a) three-dimensional elastic constants, ultimate strains and strengths and the nonlinear stress–strain curves for five unidirectional laminae and their constituents and (b) a description of 12 challenging test cases of 5 composite laminates, the lay-ups, layer thicknesses, stacking sequences and the loading conditions. The originators of 3D failure theories were requested to use the exact data provided here in their blind predictions of the test cases. The instructions issued to the contributors are also presented at the end of this article.