George S. Springer

Moisture Absorption and Desorption of Composite Materials

Expressions are presented for the moisture distribution and the mois ture content as a function of time of one dimensional homogeneous and composite materials exposed either on one side or on both sides to humid air or to water. The results apply during both moisture absorption and desorption when the moisture content and the temperature of the environ ment are constant. Test procedures are described for determining experi mentally the values of the moisture content and the diffusivity of com posite materials. A series of tests using unidirectional and π/4 Graphite T-300 Fiberite 1034 composites were performed in the temperature range 300—425 K with the material submerged both in moist air (humidity 0 to 100%) and in water. The test data support the analytical results and pro vide the moisture absorption and desorption characteristics of such com posites. Extension of the results to materials exposed to time varying envi ronmental conditions is indicated.

Thermal Conductivities of Unidirectional Materials

In this paper the composite thermal conductivities of unidirec tional composites are studied and expressions are obtained for pre dicting these conductivities in the directions along and normal to the filaments. In the direction along the filament an expression is presented based on the assumption that the filaments and matrix are connected in parallel. In the direction normal to the filaments composite thermal conductivity values are obtained first by utiliz ing the analogy between the response of a unidirectional composite to longitudinal shear loading and to transverse heat transfer; second by replacing the filament-matrix composite with an idealized ther mal model. The results of the shear loading analogy agree reason ably well with the results of the thermal model particularly at filament contents below about 60%. These results were also com pared to experimental data reported in the literature and good agreement was found between the data and those theoretical re sults that were derived for circular filaments arranged in a square packing array.

Heat of Reaction, Degree of Cure, and Viscosity of Hercules 3501-6 Resin

The heat of reaction, degree of cure, and viscosity of Hercules 3501-6 resin were measured using a differential scanning calorimeter and a disc and plate type viscometer. Expression were developed for correlating the rate of degree of cure and the viscosity with the degree of cure. Viscosities calculated by these ex pressions were compared with data reported previously, and good agreement was found between the present results and the previous data.

Strength of Mechanically Fastened Composite Joints

A method is presented for predicting the failure strength and failure mode of mechanically fastened fiber reinforced composite laminates. The method in cludes two steps. First, the stress distribution in the laminate is calculated by the use of a finite element method. Second, the failure load and the failure mode are predicted by means of a proposed failure hypothesis together with Yamadas failure criterion. A computer code was developed which can be used to calculate the maximum load and the mode of failure of joints involving laminates with different ply orientations, different material properties, and dif ferent geometries. Results generated by the present method were compared to data and to existing analytical and numerical solutions. The results of the pres ent method were found to agree well with those reported previously. Parametric studies were also performed to evaluate the effects of joint geometry and ply orientation on the failure strength and on the failure mode.

Effects of Moisture and Temperature on the Tensile Strength of Composite Materials

The ultimate tensile strengths of Thornel 300/Fiberite 1034 graphite epoxy composites were measured with material temperatures ranging from 200 K to 422 K and moisture contents from 0% (dry) to 1.5% (fully saturated). All measurements were performed using 0°, 90° and π/4 laminates. A survey was also made of the existing data showing the effects of temperature and moisture content on the tensile strength of different composites.

MOISTURE ABSORPTION OF GRAPHITE-EPOXY COMPOSITES IMMERSED IN LIQUIDS AND IN HUMID AIR.

Moisture absorption of graphite-epoxy composites immersed in liquids and in himid air were investigated. The moisture content as a function of time and temperature was measured for three materials: Fiberite T300/1034, Hercules AS/3501-5 and Narmco T300/5208. Tests were per formed a) with the materials immersed in No. 2 diesel fuel, in jet A fuel, in aviation oil, in saturated salt water, and in distilled water (in the range of 300 to 322 K) and b)with the materials exposed to humid air (in the range 322 to 366 K). The results obtained were compared to available composite and neat resin data.

Heat Transfer in Rarefied Gases

Publisher Summary This chapter presents the results of the recent analytical and experimental investigations of heat transfer in rarefied gases. It concentrates on the heat transfer through the electrically neutral nonreacting gases. The effects of ionization, dissociation, etc., that may arise in high-speed high temperature gas flows are not considered. The term “rarefied” means that the molecular mean free path is not small compared to a characteristic dimension . The parameter that describes the degree of rarefaction is the Knudsen number. In defining the Knudsen number, it is important to select the appropriate characteristic mean free path and length. When the Knudsen number is very small, then, in the vicinity of the body, the number of collisions between the molecules is large compared to the number of collisions between the molecules and the body. In this case, the usual continuum concepts are applicable and the Navier-Stokes equations and the Fourier heat conduction law are valid. When the Knudsen number becomes sufficiently large, then the continuum concepts must be modified for calculating the heat transfer. At very high Knudsen numbers where the number of collisions between the molecules and the wall is much larger than the number of collisions between the molecules, the flow is termed “free molecule.”

MOISTURE ABSORPTION OF POLYESTER-E GLASS COMPOSITES.

Moisture absorption of polyester-E glass composites immersed in liquids and in humid air were investigated. The weights of the composites as a function of exposure time and temperature were measured for three differ ent types of materials. Tests were performed a) with the materials im mersed in distilled water, in saturated salt water, in No. 2 diesel fuel, in jet A fuel, in synthetic aviation lubricant, in gasoline, and b) with the materi als exposed to humid air. The apparent maximum moisture contents and the apparent diffusivities were deduced from the data.

Resin Flow During the Cure of Fiber Reinforced Composites

Experiments were performed studying resin flow during the cure of fiber reinforced, organic matrix composites using a system in which the resin was simulated by viscous liquids and the fibers either by layers of thin rods or by layers of porous plates. The flow pattern was observed and the flow rate was measured for different applied pressures. The data were compared to the results of the Springer-Loos model and excellent agreement was found bet ween the data and the model.

Environmental Effects on Glass Fiber Reinforced Polyester and Vinylester Composites

The effects of environment on glass fiber reinforced polyester and vinylester composites immersed in liquids and in humid air were investi gated. Tests were performed at temperatures 23 C and 93 C with the materials exposed to humid air at 50 and 100 percent relative humidities, and to five different liquids: saturated salt water, No. 2 diesel fuel, lubrica ting oil, antifreeze, and indolene. Changes in weight, ultimate tensile strength, tensile modulus, short beam shear strength, and shear modulus were measured over a six month period, and the effects of the environment on these parameters were assessed.