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Results for “mixed-mode failure”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Characterization of mode 1 and mixed-mode failure of adhesive bonds between composite adherends

A combined experimental and analytical investigation of an adhesively bonded composite joint was conducted to characterize both the static and fatigue beyond growth mechanism under mode 1 and mixed-mode 1 and 2 loadings. Two bonded systems were studied: graphite/epoxy adherends bonded with EC 3445 and FM-300 adhesives. For each bonded system, two specimen types were tested: a double-cantilever-beam specimen for mode 1 loading and a cracked-lapshear specimen for mixed-mode 1 and 2 loading. In all specimens tested, failure occurred in the form of debond growth. Debonding always occurred in a cohesive manner with EC 3445 adhesive. The FM-300 adhesive debonded in a cohesive manner under mixed-mode 1 and 2 loading, but in a cohesive, adhesive, or combined cohesive and adhesive manner under mode 1 loading. Total strain-energy release rate appeared to be the driving parameter for debond growth under static and fatigue loadings.

Mall, S.↗
NASA NTRS1986

Characterization of mode I and mixed-mode failure of adhesive bonds between composite adherends

A combined experimental and analytical investigation of an adhesively bonded composite joint was conducted to characterize both the static and fatigue beyond growth mechanism under mode 1 and mixed-mode 1 and 2 loadings. Two bonded systems were studied: graphite/epoxy adherends bonded with EC 3445 and FM-300 adhesives. For each bonded system, two specimen types were tested: a double-cantilever-beam specimen for mode 1 loading and a cracked-lapshear specimen for mixed-mode 1 and 2 loading. In all specimens tested, failure occurred in the form of debond growth. Debonding always occurred in a cohesive manner with EC 3445 adhesive. The FM-300 adhesive debonded in a cohesive manner under mixed-mode 1 and 2 loading, but in a cohesive, adhesive, or combined cohesive and adhesive manner under mode 1 loading. Total strain-energy release rate appeared to be the driving parameter for debond growth under static and fatigue loadings.

Mall, S.↗
NASA NTRS1979

Delamination crack growth in unidirectional fiber-reinforced composites under static and cyclic loading

An investigation of delamination crack growth in a unidirectional composite laminate under static and fatigue loading conditions is presented. An experimental program was conducted to study failure mechanisms and characterize the crack growth rate; analytical modeling based on microscopic observations was carried out using an advanced singular finite element method of the hybrid-stress model. Using a mixed-mode failure criterion, the delamination growth under a monotonically increasing load can be predicted; the rate of delamination crack propagation under fatigue loading is directly related to the amplitudes of cyclic opening and shearing mode stress intensity factors by a power law relationship.

Wang, S. S.↗
DOE OSTI2026

Uncertainty quantification for competing failure mechanisms in unidirectionally reinforced carbon–carbon composites

Microstructure-informed finite element models play a key role in the carbon–carbon composite design process. Variability in manufacturing process parameters and experimental limitations introduce model parameter uncertainty. This study quantifies the effect of model parameter uncertainty on transverse tensile fracture behavior and proposes a methodology to predict the failure mode based on competing microscale damage mechanisms. Finite element simulations incorporate fiber–matrix interface debonding with cohesive zones and matrix damage with a smeared crack band approach in a unidirectional carbon–carbon composite. Results from a variance-based global sensitivity analysis identifies interfacial and matrix damage parameters as the primary source of variability in fracture behavior. Sobol’ indices indicate that matrix and cohesive zone strengths contribute 94% of the variance in the effective ultimate stress. A local analysis elucidates the relationship between these constituent strength parameters and failure mode by estimating the probability of cohesive, matrix, and mixed-mode dominated failure. Based on the results for 4000 simulations, 93% exhibit mixed-mode or interfacial dominated failure, which underscores the crucial role of fiber–matrix interface debonding in the transverse tensile failure of carbon–carbon composites. These uncertainty quantification results facilitate more efficient model calibration and provide a framework for microstructure-informed failure predictions in the face of manufacturing-induced uncertainty.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Finite deformation implementation of a mixed-mode single-integral type cohesive zone with reorienting surfaces of separation

To model material ductile failure and crack propagation, cohesive zone elements can be embedded along potential fracture paths in a finite element simulation. When damage criteria are met, elements in the mesh decohere, simulating the formation and propagation of a crack. In this paper, we present a novel computational algorithm based on finite deformation theory, essential to modeling crack initiation and growth in solids undergoing large deformations. This new algorithm was formulated within a Lagrangian frame of reference to extend previous cohesive zone algorithms to include modeling crack growth in finite deformation contexts. The local coordinate system, necessary for defining an embedded cohesive zone, is constructed based upon the current configuration and is updated within the nonlinear iteration process, thereby resulting in the convergence of the solution for a growing crack in a large deformation quasi-static setting. The model’s accuracy was demonstrated by comparing finite element model simulation results with the analytic case of a constant surface separation, as shown in the verification examples. The power and efficacy of the algorithm to capture large deformations during crack growth were then demonstrated with a double cantilever beam example case. It indicates that the model can be applied to a variety of physical circumstances for predicting crack initiation and growth with delamination and fracture.

42 ENGINEERING↗
NASA NTRS1985

Mixed-mode cyclic debonding of adhesively bonded composite joints

A combined experimental-analytical investigation to characterize the cyclic failure mechanism of a simple composite-to-composite bonded joint is conducted. The cracked lap shear (CLS) specimens of graphite/epoxy adherend bonded with EC-3445 adhesive are tested under combined mode 1 and 2 loading. In all specimens tested, fatigue failure occurs in the form of cyclic debonding. The cyclic debond growth rates are measured. The finite element analysis is employed to compute the mode 1, mode 2, and total strain energy release rates (i.e., GI, GII, and GT). A wide range of mixed-mode loading, i.e., GI/GII ranging from 0.03 to 0.38, is obtained. The total strain energy release rate, G sub T, appeared to be the driving parameter for cyclic debonding in the tested composite bonded system.

Rezaizadeh, M. A.↗
NASA NTRS1979

Interlaminar crack growth in fiber reinforced composites during fatigue

This paper presents an investigation of interlaminar crack growth behavior in fiber-reinforced composites subjected to fatigue loading. In the experimental phase of the study, interlaminar crack propagation rates and mechanisms were determined for the cases of various geometries, laminate parameters and cyclic stress levels. An advanced singular hybrid-stress finite element method was used in conjunction with the experimental results to examine the local crack-tip behavior and to characterize the crack propagation during fatigue. Results elucidate the basic nature of the cyclic delamination damage and relate the interlaminar crack growth rate to the range of mixed-mode crack-tip stress intensity factors. The study provides fundamental insight into the problem, reveals several important features of the interlaminar fatigue failure, and should be of practical importance in selection, testing and design of composite materials.

Wang, S. S.↗
NASA NTRS1987

Surface flaw reliability analysis of ceramic components with the SCARE finite element postprocessor program

The SCARE (Structural Ceramics Analysis and Reliability Evaluation) computer program on statistical fast fracture reliability analysis with quadratic elements for volume distributed imperfections is enhanced to include the use of linear finite elements and the capability of designing against concurrent surface flaw induced ceramic component failure. The SCARE code is presently coupled as a postprocessor to the MSC/NASTRAN general purpose, finite element analysis program. The improved version now includes the Weibull and Batdorf statistical failure theories for both surface and volume flaw based reliability analysis. The program uses the two-parameter Weibull fracture strength cumulative failure probability distribution model with the principle of independent action for poly-axial stress states, and Batdorf's shear-sensitive as well as shear-insensitive statistical theories. The shear-sensitive surface crack configurations include the Griffith crack and Griffith notch geometries, using the total critical coplanar strain energy release rate criterion to predict mixed-mode fracture. Weibull material parameters based on both surface and volume flaw induced fracture can also be calculated from modulus of rupture bar tests, using the least squares method with known specimen geometry and grouped fracture data. The statistical fast fracture theories for surface flaw induced failure, along with selected input and output formats and options, are summarized. An example problem to demonstrate various features of the program is included.

Gyekenyesi, John P.↗
NASA NTRS1987

Surface flaw reliability analysis of ceramic components with the SCARE finite element postprocessor program

The SCARE (Structural Ceramics Analysis and Reliability Evaluation) computer program on statistical fast fracture reliability analysis with quadratic elements for volume distributed imperfections is enhanced to include the use of linear finite elements and the capability of designing against concurrent surface flaw induced ceramic component failure. The SCARE code is presently coupled as a postprocessor to the MSC/NASTRAN general purpose, finite element analysis program. The improved version now includes the Weibull and Batdorf statistical failure theories for both surface and volume flaw based reliability analysis. The program uses the two-parameter Weibull fracture strength cumulative failure probability distribution model with the principle of independent action for poly-axial stress states, and Batdorf's shear-sensitive as well as shear-insensitive statistical theories. The shear-sensitive surface crack configurations include the Griffith crack and Griffith notch geometries, using the total critical coplanar strain energy release rate criterion to predict mixed-mode fracture. Weibull material parameters based on both surface and volume flaw induced fracture can also be calculated from modulus of rupture bar tests, using the least squares method with known specimen geometry and grouped fracture data. The statistical fast fracture theories for surface flaw induced failure, along with selected input and output formats and options, are summarized. An example problem to demonstrate various features of the program is included.

Gyekenyesi, J. P.↗
NASA NTRS1984

Repeatability of mixed-mode adhesive debonding

The repeatability of debond growth rates in adhesively bonded subjected to constant-amplitude cyclic loading was studied. Debond growth rates were compared from two sets of cracked-lap-shear specimens that were fabricated by two different manufacturers and tested in different laboratories. The fabrication method and testing procedures were identical for both sets of specimens. The specimens consisted of aluminum adherends bonded with FM-73 adhesive. Critical values of strain-energy-release rate were also determined from specimens that were monotonically loaded to failure. The test results showed that the debond growth rates for the two sets of specimens were within a scatter band which is similar to that observed in fatigue crack growth in metals. Cyclic debonding occurred at strain-energy-release rates that were more than an order of magnitude less than the critical strain-energy-release rate in static tests.

Everett, R. A., Jr.↗
NASA NTRS1985

Repeatability of mixed-mode adhesive debonding

The repeatability of debond growth rates in adhesively bonded subjected to constant-amplitude cyclic loading was studied. Debond growth rates were compared from two sets of cracked-lap-shear specimens that were fabricated by two different manufacturers and tested in different laboratories. The fabrication method and testing procedures were identical or both sets of specimens. The specimens consisted of aluminum adherends bonded with FM-73 adhesive. Critical values of strain-energy-release rate were also determined from specimens that were monotonically loaded to failure. The test results showed that the debond growth rates for the two sets of specimens were within a scatter band which is similar to that observed in fatigue crack growth in metals. Cyclic debonding occurred at strain-energy-release rates that were more than an order of magnitude less than the critical strain-energy-release rate in static tests.

Everett, R. A., Jr.↗
NASA NTRS1988

Computational simulation methods for composite fracture mechanics

Structural integrity, durability, and damage tolerance of advanced composites are assessed by studying damage initiation at various scales (micro, macro, and global) and accumulation and growth leading to global failure, quantitatively and qualitatively. In addition, various fracture toughness parameters associated with a typical damage and its growth must be determined. Computational structural analysis codes to aid the composite design engineer in performing these tasks were developed. CODSTRAN (COmposite Durability STRuctural ANalysis) is used to qualitatively and quantitatively assess the progressive damage occurring in composite structures due to mechanical and environmental loads. Next, methods are covered that are currently being developed and used at Lewis to predict interlaminar fracture toughness and related parameters of fiber composites given a prescribed damage. The general purpose finite element code MSC/NASTRAN was used to simulate the interlaminar fracture and the associated individual as well as mixed-mode strain energy release rates in fiber composites.

Murthy, Pappu L. N.↗
NASA NTRS1985

Comparisons of various configurations of the edge delamination test for interlaminar fracture toughness

Various configurations of Edge Delamination Tension (EDT) test specimens, of both brittle (T300/5208) and toughened-matrix (T300/BP907) graphite reinforced composite laminates, were manufactured and tested. The mixed-mode interlaminar fracture toughness, G sub C, was measured using (30/30 sub 2/30/90 sub N)sub s, n=1 or 2, (35/-35/0/90) sub s and (35/0/-35/90) sub s layups designed to delaminate at low tensile strains. Laminates were made without inserts so that delaminations would form naturally between the central 90 deg plies and the adjacent angle plies. Laminates were also made with Teflon inserts implanted between the 90 deg plies and the adjacent angle (theta) plies at the straight edge to obtain a planar fracture surface. In addition, interlaminar tension fracture toughness, GIc, was measured from laminates with the same layup but with inserts in the midplane, between the central 90 deg plies, at the straight edge. All of the EDT configurations were useful for ranking the delamination resistance of composites with different matrix resins. Furthermore, the variety of layups and configurations available yield interlaminar fracture toughness measurements needed to generate delamination failure criteria. The influence of insert thickness and location, and coupon size on G sub c values were evaluated.

Obrien, T. K.↗
NASA NTRS1978

An analysis of delamination in angle-ply fiber reinforced composites

An analytical investigation of the mechanics and failure modes of delamination initiated from a service-induced surface flaw in angle-ply fiber reinforced composites is presented. The analysis employs a hybrid-stress finite element method including a crack-tip singular element with its field variables expressed by Muskhelishvili's complex stress functions. Solutions are obtained for delaminated composites with various laminate parameters. The results elucidate unique and important characteristics of delamination crack-tip response and interlaminar stress transfer mechanisms. Of particular interest are the mixed-mode stress intensity factors associated with the delamination crack. The influence of ply orientation on KI and KII and their effects on subsequent crack extension are discussed.

Wang, S. S.↗
NASA NTRS1980

An analysis of delamination in angle-ply fiber-reinforced composites

A study of the mechanics and failure modes of delamination initiated from a surface flaw in angle-ply fiber-reinforced composites is presented. The analysis employs a hybrid-stress finite-element method including a crack-tip singular element with its field variables expressed by Muskhelishvili's complex stress functions. Solutions are obtained for the delaminated composites with various laminate parameters. The results elucidate unique and important characteristics of delamination crack-tip response and interlaminar stress transfer mechanisms. Of particular interest are the mixed-mode stress-intensity factors associated with the delamination crack. The influence of ply orientation on KI and KII and their effects on subsequent crack extension are discussed.

Wang, S. S.↗
NASA NTRS1985

Influence of the resin on interlaminar mixed-mode fracture

Both literature review data and new data on toughness behavior of seven matrix and adhesive systems in four types of tests were studied in order to assess the influence of the resin on interlaminar fracture. Mixed mode (i.e., various combinations of opening mode 1, G sub 1, and shearing mode 2; G sub 2) fracture toughness data showed that the mixed mode relationship for failure appears to be linear in terms of G sub 1 and G sub 2. The study further indicates that fracture of brittle resins is controlled by the G sub 1 component, and that fracture of many tough resins is controlled by total strain-energy release rate, G sub T. Regarding the relation of polymer structure and the mixed mode fracture: high mode 1 toughness requires resin dilatation; dilatation is low in unmodified epoxies at room temperature/dry conditions; dilatation is higher in plasticized epoxies, heated epoxies, and in modified epoxies; modification improves mode 2 toughness only slightly compared with mode 1 improvements. Analytical aspects of the cracked lap shear test specimen were explored.

Johnson, W. S.↗
NASA NTRS1984

Cyclic debonding of adhesively bonded composites

To analyze the fatigue behavior of a simple composite-to-composite bonded joint, a combined experimental and analytical study of the cracked-lap-shear specimen subjected to constant-amplitude cyclic loading was undertaken. Two bonded systems were studied: T300/5208 graphite/epoxy adherends bonded with adhesives EC 3445 and with FM-300. For each bonded system, two specimen geometries were tested: (1) a strap adherend of 16 plies bonded to a lap adherend of 8 plies, and (2) a strap adherend of 8 plies bonded to a lap adherend of 16 plies. In all specimens tested, the fatigue failure was in the form of cyclic debonding with some 0 deg fiber pull-off from the strap adherend. The debond always grew in the region of adhesive that had the highest mode I (peel) loading and that region was close to the adhesive-strap interface. Furthermore, the measured cyclic debond growth rates correlated well with total strain energy release rates G(T) as well as with its components G(I) (peel) and G(II) (shear) for the mixed-mode loading in the present study.

Mall, S.↗
NASA NTRS1987

Influence of the resin on interlaminar mixed-mode fracture

Both literature review data and new data on toughness behavior of seven matrix and adhesive systems in four types of tests were studied in order to assess the influence of the resin on interlaminar fracture. Mixed mode (i.e., various combinations of opening mode 1, G sub 1, and shearing mode 2; G sub 2) fracture toughness data showed that the mixed mode relationship for failure appears to be linear in terms of G sub 1 and G sub 2. The study further indicates that fracture of brittle resins is controlled by the G sub 1 component, and that fracture of many tough resins is controlled by total strain-energy release rate, G sub T. Regarding the relation of polymer structure and the mixed mode fracture: high mode 1 toughness requires resin dilatation; dilatation is low in unmodified epoxies at room temperature/dry conditions; dilatation is higher in plasticized epoxies, heated epoxies, and in modified epoxies; modification improves mode 2 toughness only slightly compared with mode 1 improvements. Analytical aspects of the cracked lap shear test specimen were explored.

Johnson, W. S.↗