Joseph Zahavi

Solid particle erosion of reinforced composite materials

Abstract Solid particle impingement erosion of uncoated composite materials of quartz-polyimide, glass-epoxy and quartz-polybutadiene constructions was investigated using sand from the Mediterranean Sea. The effects of the mass of sand impacted and the impact angle were determined and details of the surface damage were characterized. While progressive mass loss was observed on all materials as the mass of sand impacted increased, one glass-epoxy composite exhibited erosion which was less than that of the other composites by half an order of magnitude; this is attributed to better adhesion between the matrix and fibers, a higher percentage of fiber loading and lower porosity. This glass-epoxy composite exhibited semiductile erosion behavior with a maximum weight loss at an impingement angle of 45°–60° while the others eroded in a brittle manner with a maximum at an impingement angle of 75°–90°. The erosion process in these composites consisted of the following sequence: (1) erosion and local removal of material in the resin zones; (2) erosion in the fiber zones associated with breakage of fibers due to bending failure of unsupported sections where resin beneath these sections had been removed; (3) erosion of the interface zones between the fibers and the adjacent matrix.

Solid particle erosion of polymeric coatings

Abstract Solid particle impingement erosion of three protective coatings, a hard MIL-C-83286 polyurethane, an elastomeric MIL-C-83231 polyurethane and an elastomeric AF-C-VBW-15-15 fluorocarbon, was investigated. The effects of the impingement angle (15°–90° ) and the mass of sand impacted (200, 400 and 600 g) were examined and the response of the materials was characterized by the mass loss, surface roughness and surface morphology. In all coatings investigated, the erosion rate (i.e. the mass loss of the target) decreased with increasing impingement angle. The maximum mass loss was found at 30° while the minimum mass loss was found at normal impingement. However, in elastomeric MIL-C-83231 polyurethane and AF-C-VBW-15-15 fluorocarbon coatings the erosion rate was found to be independent of the impingement angle in the range 45°–90°. A progressive increase in the mass loss of the target coating with the amount of sand impacted was found in MIL-C-83286 polyurethane coatings at constant impingement angles. However, in MIL-C-83231 polyurethane and AF-C-VBW-15-15 fluorocarbon coatings the erosion rate (i.e. the mass change in the target) was found to be independent of the mass of sand impacted at constant impingement angles of 45°–90°. The surface roughness of the eroded coatings was found to depend on the mass loss of the target; the greater the mass loss was, the larger was the value of surface roughness observed. Erosion processes in the coatings were associated with the formation of microcracks and with microcrack propagation and intersection; these effects resulted in the local removal of fragments of coatings from the surface.

Pre-bonding technology based on excimer laser surface treatment

Abstract The application of ArF excimer laser for surface pre-treatment of polycarbonate, polyetherimide, polyaryl ether–ether–ketone (PEEK) composite, fiberglass, aluminum, copper and fused silica was investigated. Various substrates were tested with excimer laser irradiation using various parameters, such as: intensity, repetition rate, and number of pulses. The optimal laser treatment parameters were found for each material needed for achieving maximum adhesional strength of the corresponding bonded joints. Experimental results indicated that UV laser surface treatment improved significantly the adhesion strength compared to conventional treated substrates for all the materials tested. The improved adhesion was correlated with the roughening of the irradiated surface, chemical modification and removal of contamination.

Indirect damage in composite materials due to raindrop impact

Abstract Indirect damage in composite substrate materials caused by propagation and interaction of elastic compression waves from the impact of water droplets on a coated surface of the composite is described and analyzed. The damage from these waves takes the form of microcracks which are propagated along resin-fiber boundaries and extend to a considerable depth in the composite itself. The coating material may appear to be undamaged. Multiple impact of droplets results in the interaction of reflected waves from microstructural discontinuities and positive wave interferences which generate tensile stresses with an amplitude greater than the dynamic ultimate strength of the material. The protective effect of polyurethane coatings is due to damping of the stress waves and reduction in the stress at the impact surface and hence the stress which is transmitted to the substrate. In the case of nickel coatings, the modulus mismatch between the nickel and the composite substrate will reduce the transmitted stress in this system.

UV radiation exposure effects on the rain erosion resistance of coated monolithic poly(carbonate) transparencies

Abstract The results of a test program designed to evaluate the effects of accelerated UV radiation exposure on the rain erosion resistance of coated monolithic poly(carbonate) transparency materials are documented. Three different coatings for transparent poly(carbonate) were tested and examined. All materials were uniformly subjected to a velocity of 500 mile h −1 and exposed to a simulated rainfall of 1 in h −1 for specific time intervals. Selected specimens were exposed to accelerated UV radiation exposure prior to testing. Accelerated UV exposure resulted in increased coating removal as a function of rainfield exposure time and embrittlement of the poly(carbonate) substrate for two of the coatings examined. One coating apparently offered rain erosion protection as well as UV exposure protection. Data acquisition included visual observation of coating damage and removal, scanning electron microscopy examinations of the coatings and poly(carbonate) substrates and hazemeter measurements. The discussion includes rain erosion kinetics and rain erosion initiation and propagation processes.

Laser Induced Metal Deposition on Semiconductor, Metallic and Polymeric Substrates From Electroplating Solutions

This work is aimed at studying the feasibility of laser induced, high-speed, highly selective direct deposition of metals on substrates immersed in commercial electroplating solutions without masking procedures and external electric current. A Q-Switch Nd/YAG pulsed laser system and excimer UV pulsed laser systems operating respectively at wavelength of 532nm and at 193 and 248nm, were used in conjunction with commercial basic potassium gold cyanide and acidic gold tetrachloride solutions. The substrates were semiconductors (silicon, gallium arsenide and silicon carbide), metallic (platinum) and polymeric (polyimide). The morphology, structure, composition and properties of the gold deposits were examined by the SEM, TEM, X-ray, AES and ESCA techniques. Deposits were found to consist of elemental gold with thickness range from a few hundred angstroms to several micrometers, depending primarily on laser energy density and on the number of pulses. Deposition occurred wherever band gap energies (plus surface barrier) were smaller than the laser photon energy; none was observed in reverse situations, as in the cases of Si 3 N 4 and fused SiO 2 . The deposits exhibited Schottky barrier contacts on silicon, silicon carbide and gallium arsenide.