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.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/67928/2/10.1177_002199838201600505.pd

Delaminations in composite plates under impact loads

A method is presented for calculating the locations, shapes, and sizes of delaminations which occur in a fiber reinforced composite plate subjected to non-penetrating (low velocity) impact of a solid object. The plate may be simply supported, clamped, or free along its edges. A failure model of the delamination formation was developed. This model was then coupled with a finite element analysis. The model and the finite element analysis were then implemented by a computer code (IMPACT-ST) which can be used to estimate the damage initiation load and the locations, shapes, and sizes of the delaminations. Tests were performed measuring the geometries of the delaminations in graphite-epoxy, graphite-toughened epoxy, and graphite-PEEK plates impacted by a projectile with a spherical tip having masses ranging from 0.355 lbm to 0.963 lbm and velocities from 50 in/sec to 225 in/sec. The data were compared to the results of the model, and good agreements were found between the measured and the calculated delamination lengths and widths

Delaminations in composite plates caused by non-penetrating impact

A model is presented for estimating the dimensions of delaminations in continuous fiber reinforced composite plates subjected to non-penetrating (low velocity) impact of a solid object. The model is based on dimensional analysis, and results in two simple, closed form expressions, one providing the delamination length, the other the delamination width. Comparisons of delamination lengths and widths calculated by these expressions with experimental data suggest that the model predicts these dimensions with reasonable accuracy

Compression behavior of delaminated composite plates

The response of delaminated composite plates to compressive in-plane loads was investigated. The delaminated region may be either circular or elliptical, and may be located between any two plies of the laminate. For elliptical delaminations, the axes of the ellipse may be arbitrarily oriented with respect to the applied loads. A model was developed that describes the stresses, strains, and deformation of the sublaminate created by the delamination. The mathematical model is based on a two dimensional nonlinear plate theory that includes the effects of transverse shear deformation. The model takes into account thermal and moisture induced strains, transverse pressures acting on the sublaminate, and contact between the sublaminate and plate. The solution technique used is the Ritz method. A computationally efficient computer implementation of the model was developed. The code can be used to predict the nonlinear-load-strain behavior of the sublaminate including the buckling load, postbuckling behavior, and the onset of delamination growth. The accuracy of the code was evaluated by comparing the model results to benchmark analytical solutions. A series of experiments was conducted on Fiberite T300/976 graphite/epoxy laminates bonded to an aluminum honeycomb core forming a sandwich panel. Either circles or ellipses made from Teflon film were embedded in the laminates, simulating the presence of a delamination. Each specimen was loaded in compression and the strain history of the sublaminate was recorded far into the postbuckling regime. The extent of delamination growth was evaluated by C-scan examination of each specimen. The experimental data were compared to code predictions. The code was found to describe the data with reasonable accuracy. A sensitivity study examined the relative importance of various material properties, the delamination dimensions, the contact model, the transverse pressure differential, the critical strain energy release rate, and the relative growth direction on the buckling load, the postbuckling behavior, and the growth load of the sublaminate

Creep, Strength and Moisture Absorption of Adhesive Bonded FRP Joints

The effects of the environment on adhesive bonded single lap joints formed using XMC-3 and SMC-R50 composites were investigated. Tests were performed at temperatures of 23C and 93C with test coupons immersed in air, water, and 5% NaCl water mixture. The weight changes of both bonded joints (XMC-3 to SMC-R50 and SMC-R50 to SMC-R50) and unbonded materials were measured. Data were also ob tained showing the effects of moisture, temperature, and applied load on changes in weight, on creep deformation, lap shear strength, and separation modes of the joints.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68649/2/10.1177_073168448500400206.pd

Curing of Epoxy Matrix Composites

Models were developed which describe the curing process of composites constructed from continuous fiber-reinforced, thermosetting resin matrix prepreg materials. On the basis of the models, a computer code was developed, which for flat-plate composites cured by a specified cure cycle, provides the temperature distribution, the degree of cure of the resin, the resin viscosity inside the composite, the void sizes, the temperatures and pressures inside voids, and the residual stress distribution after the cure. In addition, the computer code can be used to determine the amount of resin flow out of the composite and the resin content of the composite and the bleeder. Tests were performed measuring the temperature distribution in and the resin flow out of composites constructed from Hercules AS/3501-6 graphite epoxy prepreg tape. The data were compared with results calculated with the computer code for the conditions employed in the tests and good agreement was found between the data and the results of the computer code. A parametric study was also performed to illustrate how the model and the associated computer code can be used to determine the appropriate cure cycle for a given application, which results in a composite that is cured uniformly, has a low void content, and is cured in the shortest amount of time.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66605/2/10.1177_002199838301700204.pd

Measurement of the thermal conductivity of helium up to 2100°K by the column method

The thermal conductivity of helium was measured at atmospheric pressure in the range 800–2100°K by the column method. The data could be correlated by the polynomial λ = 0.635×10−1+0.310×10−3T−0.244×10−7T2λ=0.635×10−1+0.310×10−3T−0.244×10−7T2, where λ is in watts per meters degrees Kelvin and T is in degrees Kelvin. The results obtained were compared with previous thermal conductivity measurements. The data of Desmond and Saxena and Saxena agree closely with the present results; the data of Timrot and Umanskii appear to be too low and those of Blais and Mann too high. Values for f = λ/ηCvf=λ∕ηCv, computed using measured thermal conductivities and available viscosity data, were found to agree well with classical results from kinetic theory.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70040/2/JCPSA6-58-10-4080-1.pd

High temperature–high pressure thermal conductivities of ethylene and propane

Thermal conductivities λ of ethylene and propane were measured in the temperature and pressure ranges 400–750 K and 0.1–2.65 MPa (ethylene) and 400–725 K and 0.1 to 0.6 MPa (propane). The data were correlated by expressions of the form λ=λ0(T) ×λp(P), with λ0 being a second order polynomial in temperature and λp a third (ethylene) or a fourth (propane) order polynomial in pressure. The results obtained were compared with previous thermal conductivity measurements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71313/2/JCPSA6-70-8-3948-1.pd

The Motion of Slender Particles in Shear Flow

A model was developed for calculating the motion of dilute suspensions of rigid, slender particles in a uniformly sheared viscous liquid, taking into ac count interactions between particles. The model was applied to the plane Couette flow problem in which particles are suspended in a liquid moving parallel to a plane with a uniform, shearing motion. The results of the model were compared to existing data, and good agreement was found between the calculated and experimental results. Using the model, results were also ob tained which illustrate the major effects of particle-particle interactions on the angular motion of the particles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68541/2/10.1177_073168448200100401.pd

Rotating Cylinder Apparatus for Rarefied Gas Flow Studies

A rotating cylinder type apparatus is described, suitable for determining drag in cylindrical Couette flow of rarefied gases, and for evaluating tangential momentum accommodation coefficients at gas-solid boundaries. The apparatus is equipped with a damping device using diffusion pump oil for eliminating undesirable oscillations in the system. Tangential momentum accommodation coefficients of argon on aluminum were determined with an accuracy of ± 2.5%. The results obtained indicate that the apparatus may be used over a wide pressure range, corresponding to free molecule and continuum flow conditions