Engineering topics

Daniel, Isaac M.

Publications and source records attributed to Daniel, Isaac M..

5 records

NASA NTRS1991

Micromechanical analysis of filamentary metal matrix composites under longitudinal loading

A two-material composite cylinder model (CCM) was considered for the study of the mechanical behavior at different temperatures of a fiber-reinforced silicon carbide/aluminum (SiC/Al) composite. An elastoplastic analysis of the model was performed in which the fiber was assumed to be linear elastic and the matrix elastoplastic with work-hardening. The analysis was based on the deformation theory of plasticity in conjunction with the von-Mises yield criterion. Experimental stress-strain curves of an SiC/Al composite were obtained at 24 and 288 C (75 and 550 F). The complete three-dimensional stress distribution in the composite using the CCM was determined. It was found that, in addition to longitudinal stresses, transverse stresses in both the fiber and the matrix were developed as a result of the different Poisson's ratios of the two materials. The transverse stresses, although much smaller than the longitudinal stresses, contributed to the plastic deformation of the matrix. The experimental stress-strain curves were favorably compared with the theoretical predictions.

Gdoutos, Emmanuel E.↗

NASA NTRS1989

Environmental effects on high strain rate properties of graphite/epoxy composite

The effects of hygrothermal conditions on the high-strain-rate properties of a unidirectional graphite/epoxy material, AS4/3501-6, were evaluated using standard physical and mechanical tests to determine the properties of the lamina. A time-temperature-moisture equivalence principle was applied to obtain master curves for the longitudinal, transverse, and in-plane shear moduli and corresponding strengths and ultimate strains of the specimens. It was found that the longitudinal properties of the material remained unchanged at all conditions, except for the longitudinal modulus, which showed a slight increase with temperature, moisture, and strain rate. On the other hand, all transverse and intralaminar shear properties were found to decrease with increasing temperature and moisture contents at a fixed strain rate.

Yaniv, Gershon↗

NASA NTRS1988

Height-tapered double cantilever beam specimen for study of rate effects on fracture toughness of composites

Loading rate effects on the mode I delamination fracture toughness of AS4/3501-6 graphite/epoxy are presently studied by means of a height-tapered double-cantilever beam specimen whose height contour is designed to furnish a slightly decreasing compliance with increasing crack length, in order to yield a stable and smooth crack propagation at high loading rates. This specimen geometry also allows much higher crack propagation velocities to be obtained with either uniform or width-tapered double cantilever beam specimens.

Yaniv, Gershon↗

NASA NTRS1987

Method for hygromechanical characterization of graphite/epoxy composite

An experimental method is described for measuring hygroscopic swelling strains and mechanical strains of moisture-conditioned composite specimens. The method consists of embedding encapsulated strain gages in the midplane of the composite laminate; thus it does not interfere with normal moisture diffusion. It is particularly suited for measuring moisture swelling coefficients and for mechanical testing of moisture-conditioned specimens at high strain rates. Results obtained by the embedded gage method were shown to be more reliable and reproducible than those obtained by surface gages, dial gages, or extensometers.

Yaniv, Gershon↗

NASA NTRS1987

Rate effects on delamiantion fracture toughness of a toughened graphite/epoxy

The objective of this study was to determine the effects of loading rate on interlaminar fracture toughness of T300/F-185 graphite/epoxy composite, having an elastomer-modified epoxy resin matrix. Mode I interlaminar fracture was investigated by means of uniform width and width-tapered double cantilever beam (DCB) specimens. Hinged tabs were used to insure unrestrained rotation at the free ends. Specimens were loaded at quasi-static deflection rates of up to 8.5 mm/s corresponding to crack extension rates of up to 21 mm/s. Crack extension was monitored by means of strain gages mounted on the surface of the specimen. Continuous records were obtained of load, deflection, and crack extension for determination of the strain energy release rate. The latter was calculated by means of the area method and beam analysis method, and expressed as a power law of the crack extension velocity. Results indicate that the strain energy release rate decreases with crack velocity by over 20 percent over three decades of crack velocity.

Daniel, Isaac M.↗