We have examined the wear and friction and surface hardness of the mixed phase Ti–Si–C alloy formed by excimer laser surface processing of Ti layers on SiC substrates. The friction between a ruby pin and the mixed surface shows a complex behavior depending on relative humidity, a behavior clearly moderated by the chemistry of the interface between the sliding pin and the surface. The friction is sometimes much lower and sometimes comparable to that between the ruby pin and the unalloyed substrate. Wear in the unalloyed case is characterized by fatigue fracture and flaking of the SiC surface which leads to abrasive wear of the ruby pin. In the alloyed case, a transfer film forms and even in the worst case, a smooth wear track results in the alloy and the pin is undamaged. The surface hardness is intermediate between that of the SiC and the unalloyed Ti surface layer. The wear results are understood in terms of changes in the grain boundary structure of the surface induced by the laser alloying process.

Oxynitride glasses in the Si–Zr–Na–Li–K–B–O–N system have been produced via incorporation of Si3N4 into the glass structure. This system is the oxynitride analogue of commercially available alkali resistant (AR) glasses used for concrete reinforcement. Glasses with nitrogen contents up to approximately 4 at.% have been obtained. Hardness, fracture toughness, and chemical durability were found to increase with increasing nitrogen content. Fibers were drawn from the glasses containing approximately 4 at.% nitrogen and used to produce reinforced cement composites. The microstructure of the fiber-matrix interface was examined in these samples after aging and compared to that of oxide AR glass fiber-matrix interface. Measurement of the wetting behavior of aqueous solution as a function of the nitrogen content of the glass suggests that this difference in microstructure is the result of changes in physiochemical properties of the glass surface due to the incorporation of nitrogen into the glass structure.

A general method that predicts the thermal behavior of optical fibers during the cooling stage of the drawing process was developed. The method can be used for thin diameter D < 200 μm, medium (200 μm < D < 500 μm), and thick (0.5 mm < D < 2 mm) single as well as core-clad fibers. A two-dimensional analysis implementing a finite difference method combined with the Kármán–Pohlhausen technique was performed to obtain the temperature profiles in thick fibers. This method accounted for axial and radial heat conduction, and can also be applied to thin and medium fibers. The case of the core-clad fibers was investigated to obtain the temperature profiles both in the radial and the axial directions. All results are presented in graphical form and can be used for optimization of the drawing process.

A method for making glass microspheres by the sol-gel process has been developed. Porous silica microspheres were produced at temperatures as low as 500 °C and densified silica microspheres were prepared at 800 °C. The size of the microspheres was controlled by adjusting the feed rate of the raw materials and the frequency of the droplet generator so that uniform spheres were obtained. Glass microspheres prepared by this method were characterized by Nuclear Magnetic Resonance (NMR), Differential Thermal Analysis (DTA), Thermogravimetric Analysis (TGA), and optical microscopy.

The objective of this investigation was to develop a triphasic PTC thermistor composite which incorporated a phase capable of absorbing heat at a critical temperature, and thus limiting deleterious effects associated with thermal runaway. The system chosen for study was pentaerythritol incorporated into a carbon black–polyethylene thermistor system. Pentaerythritol exhibits a first order tetragonal to cubic phase transition at 185 °C, with a 1.87 to 3.18 J/°C · g change in specific heat and a 425 J/cm3 heat of transition. Composites with room temperature resistivities as low as 0.1 Ω · m, a PTCR effect of up to six orders of magnitude, and reproducible temperature-cycling behavior were developed. The pentaerythritol introduced thermal delays up to 7 min at 185 °C and substantially increased the electrical and mechanical stability of the composites with temperature and voltage cycling. High fields imparted irreversible effects in these composites as reflected by an increase in the room temperature and high temperature resistivity.

We examine the photon emission accompanying rapid crack growth in an unfilled epoxy resin and in the same resin filled with alumina particles. The alumina particles substantially increase the toughness of the material and increase the photon emission intensities at least tenfold. We attribute the increased photon emission in the filled material to high densities of broken bonds near the alumina particles. The photon emission signals from both filled and unfilled materials show nonintegral (fractal) dimensions which are insensitive to the presence of the particles at the level of precision employed. Fractal dimension measurements of the fracture surfaces are likewise relatively insensitive to the presence of the filler, despite marked variations in apparent surface roughness. The photon emission signals were examined for the presence of chaos. Computations of the correlation exponent of Grassberger and Procaccia indicate that the photon emission fluctuations are not noise-like in character, and suggest deterministic chaos. Lyapunov exponent estimates on photon emission signals confirm the presence of chaotic processes. X-ray photoelectron spectroscopy and electron microscopy of the fracture surface indicate very little interfacial failure; i.e., fracture proceeds predominantly through the epoxy matrix in both filled and unfilled materials. Consequently, the character of the polymer matrix dominates the fracture process and therefore determines the fractal nature of the surface and the chaotic nature of the photon emission intensities in each material.

Researchers using backscattered scanning electron microscopy, along with quantitative image analysis techniques, have clearly demonstrated the existence of a highly porous interfacial region between aggregate particles and the cement paste matrix in ordinary Portland cement concrete. This paper presents the results of a digital-image-based simulation model of this interfacial zone. A dissolution-diffusion-reaction-like cycle of hydrating cement particles is directly simulated using cement particles packed around a simple nonreactive aggregate particle. The model is two-dimensional, as we are comparing to experimental results obtained on two-dimensional images of polished sections. The qualitative features seen experimentally, such as large amounts of porosity and calcium hydroxide in the interfacial zone, are accurately reproduced. A new mechanism, one-sided growth, is proposed, along with the more usual particle-packing ideas, as an explanation of the origin of the characteristic features of the interfacial zone.

Bones are biological structural materials made of dynamically adaptable tissues. They can be considered as complex natural composite materials with load bearing constituents such as osteons and interstitial lamellae cemented with weak bonding materials. In addition, they contain Haversian and Volkmann canals that are functionally needed but are structurally weak. Because of large variation in microstructure, the strength of a bone varies from bone to bone and animal to animal. In this study the applicability of Weibull statistics to fracture strength of bones has been evaluated. The statistics is based on the weakest link theory and has been used successfully for probabilistic design of critical engineering structural components. The analysis shows that the statistics is valid when applied to each type of bone and it differentiates data from different types of bones. The analysis provides an insight in terms of how nature designs its load bearing structures by the process of natural selection.