Some Physical Properties of Eight Refractory Oxides and Carbides

An investigation of eight hot-pressed refractory oxides and carbides for possible gas-turbine application was undertaken. The properties, short-time tensile strength at elevated temperatures, thermal-shock resistance, coefficient of linear expansion, and density, were determined. The compositions of the ceramics included beryllium oxide, magnesium oxide, stabilized zirconia, zircon, boron carbide, 85% silicon carbide plus 15% boron carbide, titanium carbide, and zirconium carbide. The short-time tensile strengths of these ceramics were determined at 1800° and 2200°F. Resistance to thermal shock was determined by rapid cooling in air to room temperature from 1800°, 2000°, 2200°, and 2400°F. The thermal-expansion characteristics of these materials were studied from room temperature to 1100°F.
Zirconium carbide was the strongest material at 2200°F. with a maximum short-time tensile strength of 15,850 lb. per sq. in.; however, it exhibited extremely poor resistance to oxidation. Boron carbide had a short-time tensile strength of 22,550 lb. per sq. in. at 1800°F., and was the strongest material at this temperature. Boron carbide also had very poor resistance to oxidation and was among the worst compositions investigated in its ability to resist fracture by thermal shock. The evaluation of strength of boron carbide at 2200°F. was unsuccessful because it fluxed with the grips. Titanium carbide had the best resistance to thermal shock, and had strengths of 15,850 lb. per sq. in. at 1800°F. and 9400 lb. per sq. in. at 2200°F. It was the most promising of the eight compositions investigated. Hot-pressing of these eight highly refractory bodies indicated that a density of at least 93% of theoretical density could be obtained by this fabrication method.     

CHARACTERISTICS OF ZIRCON PORCELAIN*

The manufacturing characteristics, properties, uses, and future possibilities of zircon porcelain are discussed. Any of the usua1 manufacturing processes may be used, but special glazes must be employed because zircon absorbs normal glazes: The typical properties (approximate values) are (a) linear expansion, 4.5 × 10^-6 per °C., (b) thermal conductivity, 0.012 (normal porcelain, 0.004), (c) tensile strength, 13,000 Ib. per sq. in., (d) compressive strength, 100,000 Ib. per sq. in., (e) modulus of elasticity, 25 × 10⁶ Ib. per sq. in., (f) thermal-shock resistance, good, (g) power factor at 1 mc., 0.001, and (h) dielectric constant, 9.     

PURE BERYLLIUM OXIDE AS A REFRACTORY*

The development of a pure BeO refractory is described, using pure Be(OH)₂ as the starting material. The hydroxide is calcined at 1200° (low) to 1800°C. (high), depending on the crystal size desired. The calcine is ball milled wet in a steel mill and cast at pH 4.5 to 5.0, or the powder may be dried and mixed with 14% Carbowax 4000 added as a water solution for dry pressing at 20,000 to 30,000 lb. per sq. in. The pressed product is vitreous when fired at 1800°C. but is also volatile at that temperature.     

High‐temperature tensile strength and fracture behavior of ZrB2‐SiC‐graphite composite

The tensile behavior of ZrB₂‐SiC‐graphite composite was investigated from room temperature to 1800°C. Results showed that tensile strength was 134.18 MPa at room temperature, decreasing to 50.34 MPa at 1800°C. A brittle‐ductile transition temperature (1300°C) of ZrB₂‐SiC‐graphite composite was deduced from experimental results. Furthermore, the effect of temperature on the fracture behavior of ZrB₂‐SiC‐graphite composite was further discussed by microstructure observations, which showed that tensile strength was controlled by the relaxation of thermal residual stress below 1300°C, and was affected by the plastic flow during 1300°C and 1400°C. At higher temperature, the tensile strength was dominated by the changes of microstructures.     

High-Temperature-Resistant Ceramic Adhesives

Ceramic adhesives were developed for bonding metal in the operational range 500° to 1000°F. When glassy-bond adhesives were suitably prepared and properly applied to types 302 and 17–7 PH stainless-steel specimens, shear strengths of the order of 2000 lb. per sq. in. were obtained at a test temperature of 800°F. and shear strengths of more than 800 lb. per sq. in. were obtained at 1000°F. Factors affecting adhesive strength included thermal-expansion fit between ceramic adhesive and metal, metal or metallic oxide additions to the adhesive glass, and the use of metal screens of selected wire and mesh dimensions as carriers in the adhesive joint. The ceramic adhesive could be applied to a precipitation hardenable type of stainless steel during part of the precipitation hardening treatment, which included heating the metal for various times at temperatures up to 1750°F.     

Mechanical properties of borothermally synthesized zirconium diboride at elevated temperatures

The mechanical properties of a nominally phase pure ZrB₂ ceramic were measured up to 2300°C in an argon atmosphere. ZrB₂ was hot pressed at 2000°C utilizing borothermally synthesized powder from high purity ZrO₂ and B raw materials. The relative density of the ceramics was about 95% with an average ZrB₂ grain size of 8.8 µm. The room temperature flexural strength was 447 MPa, with strength decreasing to 196 MPa at 1800°C, and then increasing to 360 MPa at 2300°C. The strength up to 1800°C was likely controlled by a combination of effects: surface damage from oxidation of the specimens, stress relaxation, and decreases in the elastic modulus. The strength above 1800°C was controlled by flaws in the range consistent with sizes of the maximum ZrB₂ grain size and the largest pores. Fracture toughness was 2.3 MPa·m^1/2 at room temperature, increasing to 3.1 MPa·m^1/2 at 2200°C. The use of higher purity starting materials improved the mechanical behavior in the ultra-high temperature regime compared to previous studies.     

Polyphenylquinoxalines containing alkylenedioxy groups

A series of new polyphenylquinoxalines (PPQ) containing alkylenedioxy units within the backbone were prepared in high molecular weight forms (η_inh = 0.82–1.5 dL/g). The glass transition temperatures ranged between 203 and 241°C, decreasing with increasing length of the alkylenedioxy groups. Solution-cast films gave tensile strength, tensile modulus, and elongation at room temperature as high as 14,400 psi, 378,000 psi, and 8.1%, respectively. The PPQ were readily compression molded to provide compact tension specimens that gave fracture energy (G_Ic) as high as 10.5 in. lb/in.² Titanium to titanium tensile shear specimens provided average strengths of 4400 psi at 26°C, 3100 psi at 177°C, and 2010 psi at 203°C. The PPQ were resistant to normal aircraft fluids but were soluble in chlorinated solvents.     

Tensile properties of two-dimensional carbon fiber reinforced silicon carbide composites at temperatures up to 2300 °C

Carbon fiber reinforced silicon carbide (C/SiC) composites are of the few most promising materials for ultra-high-temperature structural applications. However, the existing studies are mainly conducted at room and moderate temperatures. In this work, the tensile properties of a two-dimensional plain-weave C/SiC composite are studied up to 2300 °C in inert atmosphere for the first time. The study shows that C/SiC composite firstly shows linear deformation behavior and then strong nonlinear characteristics at room temperature. The nonlinear deformation behavior rapidly reduces with temperature. The Young’s modulus increases up to 1000 °C and then decreases as temperature increases. The tensile strength increases up to 1000 °C firstly, followed by reduction to 1400 °C, then increases again to 1800 °C, and lastly decreases with increasing temperature. The failure mechanisms being responsible for the mechanical behavior are gained through macro and micro analysis. The results are useful for the applications of C/SiC composites in the thermal structure engineering.     

Poly(lactide)/cellulose nanocrystal nanocomposites by high-shear mixing

There is currently considerable interest in developing stiff, strong, tough, and heat resistant poly(lactide) (PLA) based materials with improved melt elasticity in response to the increasing demand for sustainable plastics. However, simultaneous optimization of stiffness, strength, and toughness is a challenge for any material, and commercial PLA is well-known to be inherently brittle and temperature-sensitive and to show poor melt elasticity. In this study, we report that high-shear mixing with cellulose nanocrystals (CNC) leads to significant improvements in the toughness, heat resistance, and melt elasticity of PLA while further enhancing its already outstanding room temperature stiffness and strength. This is evidenced by (i) one-fold increase in the elastic modulus (6.48 GPa), (ii) 43% increase in the tensile strength (87.1 MPa), (iii) one-fold increase in the strain at break (∼6%), (iv) two-fold increase in the impact strength (44.2 kJ/m²), (v) 113-fold increase in the storage modulus at 90°C (787.8 MPa), and (vi) 10³-fold increase in the melt elasticity at 190°C and 1 rad/s (∼10⁵ Pa) via the addition of 30 wt% CNC. It is hence possible to produce industrially viable, stiff, strong, tough, and heat resistant green materials with improved melt elasticity through high-shear mixing.     

Effects of compounding and extrusion variables on degree of fusion and impact strength of PVC window profile

The effects of temperature in twin screw extrusion of a window profile compound have been studied. Compounds were made with and without an acrylic impact modifier. Fusion levels of the extruded profiles were rated from values of the rubbery plateau modulus at temperatures near 110°C. Impact strength was measured at room temperature using notched tensile specimens at 1 m/s jaw separation rate. The impact strength of these materials does not increase with fusion level once an adequate degree of gelation has been achieved. The impact-modified compound shows a dramatic improvement in impact strength when the melt temperature was increased from 319°F to 343°F. A further increase to 365°F had no effect. The compound without impact modifier exhibited no improvements in impact strength over the whole extrusion temperature range. Conflicting reports in the literature on effects of fusion level on impact strength of PVC articles probably reflect different interactions between extrusion conditions and compound composition.     

RELATION OF CRUSHING STRENGTH OF SILICA BRICK AT VARIOUS TEMPERATURES TO OTHER PHYSICAL PROPERTIES*

The failure at elevated temperatures under constant load for silica brick is reported using the Iupuy load test apparatus. The crushing strength at 1500°F, 1800°F. 2100°F, and 2400°F is recorded, as well as the crushing strength at room temperature. The size of test piece utilized normally was 1 by 1 by 2′/2 inches. A definite relationship is shown to exist between the strength at room temperature and that at elevated temperatures. The effect of variation in lime content, bats content, and fluxes is also reported. Data were obtained on brick made from three different quartzites. Additional physical data are reported to give information concerning the properties of the brick tested.     

Curing and constitutive relationships for polyester mortar

The compressive and tensile properties of polyester mortar were studied under various curing conditions, temperature, and strain rate. The curing temperature was varied from room temperature to 80°C. The behavior of polyester mortar was studied using a uniform sand with strain rate and temperature varied between 0.01 to 6 percent strain per minute and 22°C and 120°C, respectively. The strength, failure strain, modulus and stress-strain relationships of polyester mortar are influenced by the curing method, testing temperature, and strain rate to varying degrees. The influence of test variables on the mechanical properties of polyester mortar are quantified. Pretreating the aggregates with a silane coupling agent further enhances the compressive and tensile strength of the mortar. The compressive modulus and splitting tensile strength of polyester mortar are related to the compressive strength. A constitutive model is used to predict the compressive stress-strain behavior of polyester mortar.     

1,3-Dimethylol-4,5-dihydroxyethyleneurea as a Potential Alternative Binder for Plywood

Two types of commercial 1,3-dimethylol-4,5-dihydroxyethyleneurea (DMDHEU) resins were used for the first time as the binders in 3-ply plywood manufacturing. The studies were aimed at the assessment of the applicability of DMDHEU as substitute for widely used urea–formaldehyde (UF) resins. Applied press platen temperature was 120°C, 140°C, and 160°C and pressing time was 300 s. The results indicate that the DMDHEU can be used as a binder for plywood. The mechanical properties: tensile shear strength, modulus of rupture (MOR), and modulus of elasticity (MOE) were determined – i.e., > 1.0, 75–90, and 11100–18000 MPa, respectively. It was found that platen temperature 120°C was sufficient for the proper cure of the binder and to obtain dry shear strength that met the requirements of EN 310 standard. Formaldehyde release was 2.8 ± 0.6 mg?m^–2?h^–1 which complied with standards for interior grade plywood.     

Tensile behavior of unidirectional polyethylene fibers PMMA and glass fibers—PMMA composite laminates

Unidirectional (UD) composite laminates based on glass fibers (GF) and high‐performance polythylene fibers (PEF) were prepared with partially polymerized methyl methacrylate (MMA) at room temperature, followed by heating at 55°C (well below the softening point of PEF) for 2 h. The tensile strength, modulus of elasticity, fiber efficiency and strength efficiency of both the composite laminates, loaded parallel to the fibers, at the same volume fraction range, were investigated. All the properties were compared between the two composite laminates. It was observed that the measured tensile strength and modulus of elasticity deviated from the values calculated from the Rule of Mixture (ROM). The deviation was minimal at the lower volume fraction of fibers, and increased with the fiber volume. An interesting feature that was observed was that the efficiencies of PEF‐reinforced composite was higher than that of the GF‐reinforced composite at the same volume fraction of the fibers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1489–1493, 2000     

Strength of polybenzimidazole and phenolic laminate-to-metal joints

Stress concentration effects and strengths of bonded and bolted butt joints were investigated for a glass fabric polybenzimidazole lalminate at room temperatuer and 700°F for a gloass fabric phenolic laminate at room temperature and 500°F. Specimen configurations included: (1) standard tensile specimen, (2) stress concentration specimen, (3) bolted double shear butt joint, (4) bolted single shear butt joint, (5) bonded double shear butt joint and (6) bonded single shear butt joint. Both polybenzimidazole and phenolic laminates exhibited high room temperature tensile strengths and little degradation of that strength occured as a result of elevated temperature exposure. However, low joint effencies (22 to 32%) were obtained for bolted butt joint specimens. Although bonded joints exhibited higher efficiencies, they suffered from a thermal expansion mismatch between the plastic laminate and the Inconel butt plates.     

Analysis of failure mechanisms of Oxide - Oxide ceramic matrix composites

The failure mechanisms of Oxide-Oxide ceramic matrix composites AS-N610 were studied at both room temperature and high temperature using tensile and fatigue tests with and without lateral and laminar notches. The unnotched coupons had an average tensile strength of 423 MPa with elastic modulus of 97 GPa at room temperature showing a perfect elastic behaviour whereas the laminar notched samples shown similar strength of 425 MPa with elastic modulus (98 GPa) revealing pseudo-ductile behaviour. A reduction in tensile strength of the oxide ceramic matrix composites was observed at high temperatures. Thermal shock experiments revealed that the retained strength of the samples quenched from 1100 °C deteriorated by ～10 % (395 ± 15 MPa). In all samples, fracture origin was observed on the mid-plane showing a higher degree of fiber pull-out, delamination and pseudo ductile behaviour. Finite element analysis confirmed higher stress concentration on the areas of failures.     

Friction and friction-generated temperature at a polymer-metal interface

Results are presented of friction and thermal tests of molded polyimide and pyrrone polymers. The coefficient of sliding friction up to surface velocities of 2 m/sec (394 ft/min) and the coefficient of thermal expansion from 300 to 500°K (80 to 440°F) were measured. An apparatus was constructed to measure simultaneously the coefficient of sliding friction and the friction-generated temperature. Measurements were made at a nominal pressure-velocity product of 0.25 MN/msec (7100 lb/in.² × ft/min) and at temperatures between 300 and 500°K (80 and 440°F).     

The Effect of Preparation Conditions on Tensile Strength of Soda-Lime-Silica Glass Rods

A study has been made of the relationship between conditions of specimen preparation and the tensile strength of small constricted soda-lime-silica glass rods. The preparation and testing techniques were basically the same as those used in a previous investigation' except that the drawing loads were systematically varied. It was found that different loads under which specimens were drawn resulted in significant changes in tensile strength values. The average strength values varied from 62,800 lb. per sq. in. to 88,400 lb. per sq. in., depending on the drawing loads used. Maximum strength values were obtained with the highest loads. The limits of error of the strength values did not change appreciably with different drawing conditions. Rubbing the specimens with the fingers reduced the strength by approximately 32%.     

Synthetic Mica Investigations: V, A Low-Shrinkage Machinable Ceramic of Phosphate-Bonded Synthetic Mica

By using phosphoric acid as the binding agent for powdered synthetic mica, it was possible to produce by dry-pressing a glass-free machinable low-shrinkage dielectric whose properties were controllable by varying the mica com- position, the forming pressure, the firing temperature, and the phosphate content. The total shrinkage was easily maintained at less than 3%, with the transverse strength in excess of 6000 lb. per sq. in. A zero-shrinkage composition was also developed and its properties are discussed. A dense, impervious ceramic was not produced by this method; the water absorption seldom was less than 4% with forming pressures of 10,000 lb. per sq. in. or less. The dielectric characteristics of this ceramic approached those reported for hot-pressed phosphate-free synthetic mica when it had similar porosity. The dielectric loss factor was of the order of 1 to 2% at room temperature and 4 to 8% at 300°c. and 1 mc. This material is suggested as a replace- ment for natural block talc.     

Static behavior and the effects of thermal cycling in hybrid laminates

The influence of hybridization with stacking sequence variation on static stiffness, strength, ultimate strain and residual properties after thermal cycling of graphite/Kevlar 49/ epoxy and graphite/S-glass/epoxy angle-ply laminates was investigated. Tensile stress-strain curves to failure and uniaxial tensile properties were determined for all laminates. Theoretical predictions of modulus, Poisson's ratio and ultimate strain were made, based on linear lamination theory, constituent ply properties and measured strength. Reasonably good agreement was found. Stacking sequence variation showed no significant systematic influence on the measured results. Specimens containing only two 0-degree Kevlar or S-glass plies behaved linearly to failure. Specimens containing four 0-degree Kevlar or S-glass plies displayed characteristic non-linearity. One group of laminates was subjected to a tensile load and to 100 thermal cycles between room temperature and 280°F, and another group to a tensile load and 100 thermal cycles between room temperature and ?100°F. All surviving specimens were tested statically to failure to determine residual properties which were compared with the properties of uncycled specimens. Specimens containing two Kevlar or two S-glass plies behaved linearly to failure. Residual moduli in these specimens were lower than for uncycled specimens but residual strengths and ultimate strains were higher. Specimens with four Kevlar or four S-glass plies showed some nonlinear behavior. No significant differences were found between residual and uncycled values for modulus and strength.