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Brinson, H. F.

Publications and source records attributed to Brinson, H. F..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Accelerated characterization of graphite/epoxy composites

A method to predict the long-term compliance of unidirectional off-axis laminates from short-term laboratory tests is presented. The method uses an orthotropic transformation equation and the time-stress-temperature superposition principle. Short-term tests are used to construct master curves for two off-axis unidirectional laminates with fiber angles of 10 deg and 90 deg. In addition, analytical predictions of long-term compliance for 30 deg and 60 deg laminates are made. Comparisons with experimental data are also given.

Griffith, W. I.↗
NASA NTRS1979

The viscoelastic behavior of a composite in a thermal environment

A proposed method for the accelerated predictions of modulus and life times for time dependent polymer matrix composite laminates is presented. The method, based on the time temperature superposition principle and lamination theory, is described in detail. Unidirectional reciprocal of compliance master curves and the shift functions needed are presented and discussed. Master curves for arbitrarily oriented unidirectional laminates are predicted and compared with experimantal results obtained from master curves generated from 15 minute tests and with 25 hour tests. Good agreement is shown. Predicted 30 deg and 60 deg unidirectional strength master curves are presented and compared to results of creep rupture tests. Reasonable agreement is demonstrated. In addition, creep rupture results for a (90 deg + or - 60 deg/90 deg) sub 2s laminate are presented.

Morris, D. H.↗
NASA NTRS1979

A correlative study between analysis and experiment on the fracture behavior of graphite/epoxy composites

The paper compares the fracture behavior of a composite material by using the analytical models of Waddoups et al. (1971), Whitney and Nuismer (1974, 1975), and Snyder and Cruse (1975) with experimental results from tests performed on center-notched tensile strips. Laminate configurations of (0 deg)8s, (0 deg/90 deg)4s, (+ and -45 deg)4s, and (0 deg/+ and -45 deg/0 deg)2s from T300/934 graphite/epoxy are tested. These particular configurations are used so that the effect of various degrees of anisotropy can be studied. The procedure adopted uses the results from one test for crack size aspect ratio to predict the results of tests of other aspect ratios. For those methods that use a characteristic dimension, predictions are made by assuming the magnitude of this dimension to be constant. The validity of this assumption for a laminate is assessed by comparing predicted and experimental results. Analytical models using a characteristic dimension are compared to the model developed by Cruse (1973).

Yeow, Y. T.↗
NASA NTRS1979

The fracture behavior of graphite/epoxy laminates

The results of uniaxial tensile tests conducted on a variety of graphite/epoxy laminates containing narrow rectangular slits and square or circular holes with various aspect ratios are discussed. The techniques used to study stable-crack or damage-zone growth - namely, birefringence coatings, COD gages, and microscopic observations are discussed. Initial and final-fracture modes are discussed as well as the effect of notch size and shape and laminate type on the fracture process. Characteristic lengths are calculated using the point, average and inherent flaw theories and comparisons with observations are discussed. Further, the effect of flaw geometry on stress states and deformations is assessed.

Yeow, Y. T.↗
NASA NTRS1979

Time-temperature behavior of a unidirectional graphite/epoxy composite

A testing program to determine the time-temperature response of unidirectional T300/934 graphite/epoxy materials is presented. The short-term creep test results of tension specimens with the load at various angles to the fiber direction and at various temperatures are reported, showing that the material is elastic at all temperatures when the fiber is in the load direction. However, when the load is transverse to the fibers, the viscoelastic response varies from small amounts at room temperature to large amounts at temperatures above the 180 C transition temperature. The time-temperature superposition principle or the method of reduced variables were used to determine compliance master curves for each fiber angle, and a viscoelastic analog to the elastic orthotropic transformation equation was used incrementally to predict the master curves for the tensile compliance of the off-axis specimen.

Yeow, Y. T.↗
NASA NTRS1978

A new experimental method for the accelerated characterization of composite materials

The use of composite materials for a variety of practical structural applications is presented and the need for an accelerated characterization procedure is assessed. A new experimental and analytical method is presented which allows the prediction of long term properties from short term tests. Some preliminary experimental results are presented.

Yeow, Y. T.↗
NASA NTRS1978

The time-temperature behavior of a unidirectional graphite/epoxy composite

A testing program to determine the time-temperature response of undirectional graphite/epoxy materials is described. Short-term creep test results of strip tensile specimen with the load at various angles to the fiber direction and at various temperature levels are reported. It was shown that the material is elastic at all temperature levels when the fiber is in the load direction. On the other hand, when the load is transverse to the fibers, the viscoelastic response was shown to vary from small amounts at room temperature to large amounts for temperatures in excess of 180 C for other fiber angles, the response was similar to the latter.

Yeow, Y. T.↗
NASA NTRS1978

A comparison of simple shear characterization methods for composite laminates

Various methods for the shear stress/strain characterization of composite laminates are examined and their advantages and limitations are briefly discussed. Experimental results and the necessary accompanying analysis are then presented and compared for three simple shear characterization procedures. These are the off-axis tensile test method, the (+/- 45 deg)s tensile test method and the (0/90 deg)s symmetric rail shear test method. It is shown that the first technique indicates the shear properties of the graphite/epoxy laminates investigated are fundamentally brittle in nature while the latter two methods tend to indicate that these laminates are fundamentally ductile in nature. Finally, predictions of incrementally determined tensile stress/strain curves utilizing the various different shear behaviour methods as input information are presented and discussed.

Yeow, Y. T.↗
NASA NTRS1978

A new experimental method for the accelerated characterization of composite materials

A method which permits the prediction of long-term properties of graphite/epoxy laminates on the basis of short-term (15 min) laboratory tests is described. Demonstration of delayed viscoelastic fracture in one laminate configuration, and data on the time and temperature response of a matrix-dominated unidirectional laminate contributed to a characterization of the viscoelastic process in the graphite/epoxy composites. Master curves from short-term tests of certain laminate configurations can be employed to generate long-term master curves. In addition, analytical predictions from short-term results can be used to predict long-term (25-hour) laminate properties.

Brinson, H. F.↗
NASA NTRS1977

An experimental investigation on the tensile moduli and strengths of graphite/epoxy laminates

The results of a series of tensile tests on some graphite/epoxy laminates, at rates varying from 0.002 to 2 in./min are examined. The loads were applied at various angles to the fiber directions in each case. The rate-dependent behavior of the stress-strain response is assessed. Evidence is presented to indicate that failure first occurs on inner plies, and that, in some cases, moduli increase with increasing stress (or strain) level. Lamination theory is used to predict the moduli, and comparisons with experiment are given. This theory is also used in conjunction with three failure theories to predict ultimate strengths (with varying degrees of success). Further, two approaches to ply unloading after first-ply failure are used and discussed. One is a standard method found in the literature while the other is a proposed 'strength-of-materials' type of technique which is computationally much simpler.

Yeow, Y. T.↗
NASA NTRS1977

A study of damage zones or characteristic lengths as related to the fracture behavior of graphite/epoxy laminates

Uniaxial tensile tests conducted on a variety of graphite/epoxy laminates, containing narrow rectangular slits, square or circular holes with various aspect ratios are discussed. The techniques used to study stable crack or damage zone growth--namely, birefringence coatings, COD gages, and microscopic observations are discussed. Initial and final fracture modes are discussed as well as the effect of notch size and shape, and laminate type on the fracture process. Characteristic lengths are calculated and compared to each other using the point, average and inherent flaw theories. Fracture toughnesses are calculated by the same theories and compared to a boundary integral equation technique. Finite width K-calibration factors are also discussed.

Yeow, Y. T.↗
NASA NTRS1977

A comparison of simple shear characterization methods for composite laminates

Various methods for the shear stress-strain characterization of composite laminates are examined, and their advantages and limitations are briefly discussed. Experimental results and the necessary accompanying analysis are then presented and compared for three simple shear characterization procedures. These are the off-axis tensile test method, the + or - 45 degs tensile test method and the 0 deg/90 degs symmetric rail shear test method. It is shown that the first technique indicates that the shear properties of the G/E laminates investigated are fundamentally brittle in nature while the latter two methods tend to indicate that the G/E laminates are fundamentally ductile in nature. Finally, predictions of incrementally determined tensile stress-strain curves utilizing the various different shear behavior methods as input information are presented and discussed.

Yeow, Y. T.↗
NASA NTRS1977

An experimental study of the fracture behavior of laminated graphite/epoxy composites

The results of an experimental investigation on the fracture behavior of unidirectional and multidirectional laminated graphite/epoxy composites is reported. Critical tensile fracture stresses for constant head rate uniaxial specimens containing single-edge notches, double-edge notches, and centrally located circular holes are presented. Results are reported for loads and notches at various angles to the fiber direction. Evidence of notch sensitivity and stable crack growth is presented. Self-similar crack growth is shown to occur for only a limited set of circumstances. Critical stresses are compared to the theories of Waddoups et al and Whitney et al. These comparisons are presented using isotropic and orthotropic stress concentration factors together with a finite width correction factor. The results tend to show that use of only isotropic correction factors allow good correlation between theory and experiment.

Brinson, H. F.↗
NASA NTRS1976

Stress-strain and failure properties of graphite/epoxy laminates

The results of a series of tensile tests on graphite/epoxy laminates at rates varying from 0.002 in/min to 2 in/min are reported. The loads are applied at various angles to the fiber directions in each case. The rate dependent behavior of the stress-strain response is assessed. Evidence is presented to indicate that failure first occurs on inner piles. Also, evidence is presented to indicate that, in some cases, moduli increase with increased stress or strain level. The lamination theory is used to predict moduli and comparisons with experiment are given. Also, the lamination theory is used in conjunction with three failure theories to predict ultimate strengths with varying degrees of success.

Yeow, Y. T.↗
NASA NTRS1976

Rate and time dependent behavior of structural adhesives

Studies on two adhesives (Metlbond 1113 and 1113-2) identified as having applications in the bonding of composite materials are presented. Constitutive equations capable of describing changes in material behavior with strain rate are derived from various theoretical approaches. It is shown that certain unique relationships exist between these approaches. It is also shown that the constitutive equation derived from mechanical models can be used for creep and relaxation loading. A creep to failure phenomenon is shown to exist and is correlated with a delayed yield equation proposed by Crochet. Loading-unloading results are presented and are shown to correlate well with the proposed form of the loading-unloading equations for the modified Bingham model. Experimental results obtained for relaxation tests above and below the glass transition temperature are presented. It is shown that the adhesives obey the time-temperature superposition principle.

Renieri, M. P.↗
NASA NTRS1975

An investigation of the failure and fracture behavior of graphite/epoxy laminates

A fundamental investigation of the fracture behavior of fiber reinforced composites is discussed. It is suggested that experimental and analytical investigations should compliment each other. Further, it is suggested that in order to understand and mathematically model composite fracture it is necessary to explore, understand and characterize the stress-strain behavior of each type of laminate tested from initial loading to incipient fracture. That is, it is not only necessary to perform fracture studies but it is necessary to perform stress-strain characterization and failure studies as well. For this reason a literature survey is presented in which these three elements are discussed. An experimental program to determine tensile properties of unnotched and notched unidirectional and multi-directional laminates composed of Hercules AS Fiber and 3501 Resin is described. Experimental unnotched moduli and strengths are presented, discussed and compared to lamination theory predictions. It is shown that rate effects are small and that lamination theory gives good results for moduli but not for strengths.

Brinson, H. F.↗
NASA NTRS1975

Rate and time dependent failure of structural adhesives

Studies on two adhesives (Metlbond 1113 and 1113-2) identified as having important applications in the bonding of composite materials are presented. A testing program to ascertain stress-strain, strain-rate, time, yield, and/or failure behavior of these materials in bulk form using uniaxial tensile constant strain-rate, creep, and relaxation tests is described. The stress-strain behavior of each material is shown to be significantly rate dependent. A rate dependent stress whitening (crazing) phenomenon occurs prior to either yield or fracture. A region of linear elasticity, a region of viscoelasticity, and the onset of yielding are identified in the stress-strain behavior. The linear elastic limit and the yield point are shown to be rate dependent and agree well with an empirical equation proposed by Ludwik. A creep to failure phenomenon is shown to exist and is correlated with a delayed yield equation proposed by Crochet. Analytical predictions based on a modified Bingham model are shown to agree well with experimental stress-strain strain-rate data. Analytical predictions based on a modified Ramberg-Osgood equation are also shown for comparison purposes.

Brinson, H. F.↗