EFFECTS OF LARGE DAMAGE ON RESIDUAL STRENGTH OF CARBON FIBER REINFORCED COMPOSITE LAMINATES A Thesis by (original) (raw)

Failure assessment on central-sharp notched carbon/epoxy laminates

Materials & Design, 2010

Fracture models to predict the strength of laminated composites having sharp notches demand the unnotched strength and the critical damage size ahead of the notch. The critical damage size, in general, depends on the material, geometry of the specimen and size of the sharp notch. The extraordinary success of a fracture model lies in its ability to combine a theoretical framework with experimentally measured quantities. Modifications are made in one of the stress-fracture criteria known as the point stress criterion for accurate prediction of notched tensile strength of composite laminates containing sharp notches. To examine the adequacy of these modifications, fracture data of central-sharp notched carbon/epoxy composite laminates with various lay-ups are considered. The notched strength estimates are found to be close to the test results. The modified point stress criterion is very simple and accurate in predicting the notched tensile strength of laminated composites.

A Progressive Damage Methodology for Residual Strength Predictions of Notched Composite Panels

Journal of Composite Materials, 1999

The translaminate fracture behavior of carbon/epoxy structural laminates with through-penetration notches was investigated to develop a residual strength prediction methodology for composite structures. An experimental characterization of several composite materials systems revealed a fracture resistance behavior that resembles the R-curve behavior exhibited by ductile metals. Fractographic examinations led to the postulate that the damage growth resistance was primarily due to fractured fibers in the principal load-carrying plies being bridged by intact fibers of the adjacent plies. The load transfer associated with this bridging mechanism suggests that a progressive damage analysis methodology will be appropriate for predicting the residual strength of laminates with through-penetration notches. A progressive damage methodology developed by the authors was used to predict the initiation and growth of matrix cracks and fiber fracture. The residual strength predictions for different...

Notched strength of carbon fibre/epoxy composite laminates with a circular hole

Forschung im Ingenieurwesen, 2000

This paper improves the two stress fracture criteria proposed by Whitney and Nuismer (known as the point stress criterion and the average stress criterion) to predict the strength of composite laminates with a circular hole. In the point stress criterion, it is assumed that the failure occurs when the stress over some distance (do) away from the notch is equal to or greater than the unnotched laminate strength. In the average stress criterion it is assumed that failure occurs when the average stress over some distance (a0) ahead of the notch equals the unnotched laminate strength. Both stress fracture criteria are two parameter models based on the unnotched strength (a0) and a characteristic dimension (do or a0). A simple relation is used for the characteristic length to improve the accuracy while evaluating the notched strength of carbon/ epoxy composite laminates. The analytical results are compared well with the existing test results of AS4-carbon/ 948 A1 epoxy [0/9014 s and [0/4-45/9012 s composite laminates with various hole diameters and specimen widths. Kerbfestigkeit von Kohle.faser/Epoxid-Verbund-Laminaton mit runden Offnungen Zusammenfassung In diesem Artikel wird eine verbesserte Form der Bruchspannungskriterien yon Whitney und Nuismer vorgestellt, die ftir die Berechnung der Spannungen in Verbundiaminaten verwendet wird, weiche eine runde 0ffnung aufweisen. Der Ansatz mit einem lokalen spannungskriterium geht davon aus, dab ein Versagen des Werkstoffes dann auffritt, sobald die Spannung in einer bestimmmten Entfernung do yon der Kerbe die Festigkeit des ungekerbten Laminates tibserschreitet. Der Ansatz des mittieren Spannungskriterium legt zugrunde, dab ein Materialversagen dann auftritt, wenn die mittiere Spannung in einer bestimmten Entfernung a0 yon der Einkerbung die Festigkeit des ungekerbten Laminates tiberschreitet. Beide Bruchspannungsansfitze sind zweiparametrische Berechnungsansfitze basierend auf der Festigkeit a0 des kerbfreien Material und einer

Size Effects on the Strength of Notched Composites

This paper examines the use of a continuum damage model to predict strength and size effects in notched carbon-epoxy laminates. The effects of size and the development of a fracture process zone before final failure are identified in an experimental program. The continuum damage model is described and the resulting predictions of size effects are compared with alternative approaches. The results show that the continuum damage model is the most accurate technique to predict size effects in composites. Furthermore, the continuum damage model does not require any calibration and it is applicable to general geometries and boundary conditions.

Notched strength prediction of laminated composite under tensile loading

Materials Science and Engineering: A, 2002

Notched strength of composite material with different type of irregularities has been estimated analytically by many researchers and scholars. Some models are extremely complicated and leads to a cumbersome calculation process and others are of limited use. This intrigued authors to seek an estimation which is simple and accurate. This paper represents statistical approach for prediction of notch strength of composite laminates of different lay-ups containing a central crack using point stress criterion and average stress criterion. For calculation of characteristic lengths for point stress criterion and average stress criterion, different expressions are used which are very simple and accurate. Final equations for notched strength of laminated composites are in the simple polynomial form and can simplify further calculations. Results are compared with experimental data of graphite/epoxy composite and data obtain from improved inherent flaw model. The notched strength estimations are found to be within range of tested and improved inherent flaw model values.

A Comprehensive Study on Damage Tolerance Properties of Notched Composite Laminates

1988

: This final report contains the results of an investigation on matrix-related damage mechanisms in notched composite laminates. The theoretical approach taken follows the principles of micromechanisms and the mechanics of brittle fracture at the descriptive level considered valid for the so-called ply-elasticity. Namely, the laminate is basically treated as a 3-dimensional elastic solid which is made of distinctly anisotropic layers. Brittle fracture can initiate and propagate within any layer having a weaker axis of material anisotropy, and within any one of the weaker layer interfaces due to the 3-dimensional interlaminar stresses. Owing to the particular microstructure of the laminate, growth of such sublaminate cracks constitutes a load- or time-dependent evolutionary process. A computer simulation methodology is developed to describe the modes and the extent of damage caused initially by the presence of the notch, and subsequently by the damages themselves. Experiment using a ...

A Finite Element Failure Model for Notched Laminated Composites Loaded in Compression

Advanced Composites Letters, 1994

This paper describes a progressive damage failure model which is making an attempt to predict damage growth and ultimate compressive strength of notched laminates subjected to uniaxial compression. A non-linear finite element programme is developed to perform the ply-by-ply stress analysis and numerical results are compared with existing experimental data [1,2]; the agreement is acceptable.

Measuring the notched compressive strength of composite laminates: Specimen size effects

Composites Science and Technology, 2008

Large fibre reinforced composite structures can give much lower strengths than small test specimens, so a proper understanding of scaling is vital for their safe and efficient use. Small size (scale) Measuring the notched compressive strength of composite laminates: Specimen size effects Abstract Large fibre reinforced composite structures can give much lower strengths than small test specimens, so a proper understanding of scaling is vital for their safe and efficient use. Small size (scale) specimens are commonly tested to justify allowable stresses, but could be dangerous if results are extrapolated without accounting for scaling effects. On the other hand * Corresponding author. Tel.: +44 (0)114 222 7811, Fax: 0044(0)114 2227836, c.soutis@sheffield.ac.uk Manuscript unidirectional specimens thicker than 2 mm is found to be limited by the stress concentration developed at the end tabs and manufacturing induced defects in the form of ply waviness, fibre misalignment and voids rather than specimen size (scaling). In the open hole specimens, for both lay-ups, the strength reduction observed is due to hole size effect rather than specimen thickness or volume increase. The open hole (notched) compressive strength results obtained compare favourably to predictions by a linear softening cohesive zone fracture model developed in earlier work by the second author.

Progressive Damage Modeling of Notched Composites

2016

There is an increased interest in using non-crimp fabric reinforced composites for primary and secondary structural components in high performance automobile applications in order to accomplish desired mass savings. However, one of the main challenges in implementing these composites is the lack of understanding of damage progression under a wide variety of loading conditions for general configurations. Towards that end, researchers at GM and NASA are developing new damage models to predict accurately the progressive failure of these composites. In this investigation, the developed progressive failure analysis model has been applied to study damage progression in center-notched and open-hole tension specimens for various laminate schemes. A segment of this effort was focused on a detailed study with respect to the effect of element size on the analysis outcome, which is presented here.