A COMPARISON OF THE UNIFORMITY OF STRENGTH AND TEXTURE OF FIRE BRICK MADE BY DIFFERENT PROCESSES1

By assuming that the “deviations from the average” of the strengths and permeabilities of individual bricks of any one brand are governed by the laws of chance, a comparison of the uniformity of strength and texture of a number of brands of brick made by different processes is obtained. Of the brands examined, those made by the stiff-mud process are found to be more uniform in strength and less uniform in structure than those made by the dry-press process. The hand-made bricks show quite a variation in both strength and texture, whereas one brand of brick made by a semi-dry process (English type machine) shows good uniformity in both strength and texture.     

Preliminary studies of the relation between the carbon texture and the strength of metallurgical coke

Preliminary attempts to relate the carbon texture to the tensile strength of metallurgical cokes are described. Two series of cokes made by carbonizing blended coal charges in pilot scale ovens were examined. The diametral compression test was used to determine the tensile strength of the cokes and the composition of the coke carbon was measured by applying a point-counting technique to the examination of atomic-oxygen etched surfaces. The strengths and textural compositions could be related by a single equation derived by multi-linear regression analysis.     

Statistical analysis of impact-fracture characteristics and microstructure of industrial Portland cement clinkers

Impact is the dominant breakage mode in most industrial grinding mills used in cement manufacture. The physical amenability of two industrial Portland cement clinkers to size reduction was determined through measurement of their fracture strengths under impact loading. It was found that the fracture strength of clinker is strongly dependent on size, which is consistent with the increasing expenditure of energy in fine grinding. Also, it was observed that the measured fracture strengths could be well described by either single or multiple Weibull distributions. The appearance of these distributions was consistent with the variability in the composition and microstructure of the clinker nodules, observed in a detailed examination under the microscope. Possible reasons for the appearance of these populations are given. It is concluded that the fracture strength of clinker is generally determined by porosity at coarser nodule sizes and by mineralogy and texture at finer sizes.     

Adhesion of Different Concrete Repair Systems Exposed to Different Environments

This article presents the results of experiments conducted to assess the effects of aging under dry laboratory conditions, underwater storage, cyclic freeze-thaw, and temperature changes on the adhesion between the repair and the substrate concrete. The repair systems considered for these studies included ordinary sand/cement (S/C) mortar, with and without bonding agents, two polymer modified cementitious mortars, and two resinous mortars. The specimens were concrete slabs of 600 × 300 × 100 mm dimensions with saw cut face 600 × 300 mm on which a repair layer of 20 mm had been applied. In order to eliminate the effects of surface texture and surface strength of the concrete on the adhesion of repair systems, repair applied surfaces were all saw cut surfaces of concrete with 28-day design compressive strength of 65 MPa. Tensile bond strengths of these specimens were measured using a direct tensile test (pull-off) method. The results indicated that the tensile bond strengths of different repair systems under dry laboratory conditions, and stored underwater, ranged from 1.51 to 5.27 Mpa. Exposure to 300 cycles of freeze-thaw and to 200 cycles of temperature changes resulted in 6 to 100 percent reduction in their tensile bond strengths.     

Adhesion of Different Concrete Repair Systems Exposed to Different Environments

This article presents the results of experiments conducted to assess the effects of aging under dry laboratory conditions, underwater storage, cyclic freeze-thaw, and temperature changes on the adhesion between the repair and the substrate concrete. The repair systems considered for these studies included ordinary sand/cement (S/C) mortar, with and without bonding agents, two polymer modified cementitious mortars, and two resinous mortars. The specimens were concrete slabs of 600 × 300 × 100 mm dimensions with saw cut face 600 × 300 mm on which a repair layer of 20 mm had been applied. In order to eliminate the effects of surface texture and surface strength of the concrete on the adhesion of repair systems, repair applied surfaces were all saw cut surfaces of concrete with 28-day design compressive strength of 65 MPa. Tensile bond strengths of these specimens were measured using a direct tensile test (pull-off) method. The results indicated that the tensile bond strengths of different repair systems under dry laboratory conditions, and stored underwater, ranged from 1.51 to 5.27 Mpa. Exposure to 300 cycles of freeze-thaw and to 200 cycles of temperature changes resulted in 6 to 100 percent reduction in their tensile bond strengths.     

Study of Some of the Factors Affecting the Mechanical Properties of Zinc Polycarboxylate Cement

The variation of the tensile and compressive strength of a zinc polycarboxylate cement with annealing temperature was studied in the temperature range from room temperature up to 160°C. The effects of powder/liquid ratio and mixing temperature were also investigated. The results obtained showed that both tensile and compressive strengths increase with increasing powder/liquid ratio. Also the cement strength increases with annealing temperature to a certain limit. It was also found that the strength depends on the mixing temperature and shows its maximum value at room temperature. The reasons for the changes of both tensile and compressive strengths due to the previously mentioned factors are discussed.     

Relationship between the Strength of Ceramic/Metal Joints in Tensile and Three-Point Bending

The tensile strength and the three-point bending strength of Si₃N₄/Al/Invar joints were compared. The fracture modes in both tests were almost the same. Statistical treatments of the strengths showed that both strengths had a similar Weibull slope of ∼6. The three-point bending strength was 2.5 times greater than the tensile strength. This magnification was slightly greater than that obtained from the relation of the effective areas in both tests.     

Effect of Melting History on the Mechanical Properties of Glass: I, Role of Melting Time and Atmosphere

The pristine strength of 0.5Li₂O·0.5K₂O·2SiO₂ glass measured in 3-point bending under liquid nitrogen was studied as a function of melting time and atmosphere at a constant melting temperature. The atmosphere over the melt was one of the most important parameters affecting the pristine strength. The most significant time-dependent melting effects and the highest strengths resulted from melting in a dry atmosphere of O₂ or air. In contrast, vacuum-melted and Ar-melted glasses had the lowest strengths. Melting in N₂ or CO₂ led to intermediate strengths. The presence of water vapor in the atmosphere during melting was detrimental to strength in those cases where very high strengths had been obtained with dry gases. The introduction of water vapor into those gases which in the dry state had led to low-strength glasses did not significantly affect the strength. The effects of the atmosphere in leading to oxygen-deficient or excess-oxygen glasses on the formation or dissolution of microheterogeneous regions were correlated with the pristine strengths of the glasses.     

Strength of brittle materials in moderately corrosive environments

The strengths of four brittle materials―cordierite glass ceramic, fused silica, silicon, and polycrystalline alumina were measured after exposure to weakly corrosive water and moderately corrosive buffered HF (BHF) solution. Exposure to water did not alter the strengths in subsequent inert strength tests and decreased the strengths in reactive strength tests. Exposure to BHF increased the strengths in both tests, but only after an incubation exposure time. Prior to the incubation time, the BHF had the same effect as water, suggesting that the bond rupture kinetics were unaffected. Examination of strength‐controlling indentation flaws after the incubation time showed clear corrosive effects on the flaw geometry indicative of reductions in the indentation residual stress fields. The implication is that moderately corrosive environments increase the strength or lifetime of a brittle component by reducing the crack driving force via flaw alteration and do not, as perhaps expected, decrease the strength or lifetime through enhanced chemical reactivity.     

Forming Textured Microstructures via the Gelcasting Technique

Crystallographically textured samples of iron titanate were produced by gelcasting in the presence of a strong magnetic field. Texture was assessed by measuring X-ray pole figures on samples that were cast in different orientations relative to the applied field. Specimens in this study exhibit fiber-type texture, with the b -axes aligned parallel to the applied field. Peak texture strengths were on the order of 3 and 48 multiples of a random distribution (MRD) when processed in a 3.2 and 8.4 T magnetic field, respectively. This study shows that a combination of gelcasting with magnetic-field-assisted processing provides a convenient method for fabricating samples which can be used to study the role of crystallographic texture on the physical properties of polycrystalline ceramics, e.g., their elastic or fracture behavior.     

Benchmark tests on adhesive strengths in butt, single and double lap joints and double-cantilever beams

The RC99 committee of the Japan Society for Mechanical Engineers conducted the benchmark tests on strengths of adhesive joints using different testing methods. The effects of joint configuration, loading mode, adherend yield strength and so on, on the strength and data scatter were investigated using two typical epoxy adhesives. The strengths obtained by various tests were compared with each other. The relationships among strengths of butt, single lap and double lap joints and fracture toughness were given. Thirteen member institutes of the committee participated in this project. The benchmark results allow us to recognize that the joint strengths are strongly affected by the curing process. The key to obtaining the appropriate joint strength, is precise temperature control inside the adhesive layer for curing. Toughened adhesives do not always give higher joint strengths than untoughened adhesives. The yield strength of adherends much affects the observed lap joint strength of adhesives.     

Multi‐Scale Effects in the Strength of Ceramics

Multiple length‐scale effects are demonstrated in indentation‐strength measurements of a range of ceramic materials under inert and reactive conditions. Meso‐scale effects associated with flaw disruption by lateral cracking at large indentation loads are shown to increase strengths above the ideal indentation response. Micro‐scale effects associated with toughening by microstructural restraints at small indentation loads are shown to decrease strengths below the ideal response. A combined meso‐micro‐scale analysis is developed that describes ceramic inert strength behaviors over the complete indentation flaw size range. Nano‐scale effects associated with chemical equilibria and crack velocity thresholds are shown to lead to invariant minimum strengths at slow applied stressing rates under reactive conditions. A combined meso‐micro‐nano‐scale analysis is developed that describes the full range of reactive and inert strength behaviors as a function of indentation load and applied stressing rate. Applications of the multi‐scale analysis are demonstrated for materials design, materials selection, toughness determination, crack velocity determination, bond rupture parameter determination, and prediction of reactive strengths. The measurements and analysis provide strong support for the existence of sharp crack tips in ceramics such that the nano‐scale mechanisms of discrete bond rupture are separate from the larger scale crack driving force mechanics characterized by continuum‐based stress‐intensity factors.     

Evaluation of fiber surfaces treatment and sizing on the shear and transverse tensile strengths of carbon fiber-reinforced thermoset and thermoplastic matrix composites

The mechanical performance of advanced composite materials depends to a large extent on the adhesion between the fiber and matrix. This is especially true for maximizing the strength of unidirectional composites in off-axis directions. The materials of interest in this study were PAN-based carbon fibers (XA and A4) used in combination with a thermoset (EPON 828 epoxy) and a thermoplastic (liquid crystal poymer) matrix. The effect of surface treatment and sizing were evaluated by measuring the short-beam shear (SBS) and transverse flexural (TF) tensile strengths of unidirectional composites. Results indicated that fiber surface treatment improves the shear and trasverse tensile strengths for both thermosetting and thermoplastic matrix/carbon fiber-reinforced unidirectional composites. A small additional improvement in strengths was observed as the result of sizing treated fibers for the epoxy composites. Scanning electron microscope photomicrographs were used to determine the location of composite failure, relative to the fiber-matrix interface. Finally, the epoxy composites SBS and TF strengths appear to be limited to the maximum transeverse tensile strength of the epoxy matrix, while the thermoplastic composite SBS and TF strengths are limited by the LCP matrix shear and transverse tensile strengths, respectively.     

三维编织PE-UHMW纤维增强PMMA复合材料的力学性能研究

采用真空浸渍法制备了三维编织超高相对分子质量聚乙烯(PE-UHMW3D)/聚甲基丙烯酸甲酯(PMMA)复合材料，重点研究了该复合材料的力学性能、纤维体积含量对复合材料力学性能的影响以及吸湿前后力学性能的对比。研究表明，PE-UHMW3D/PMMA复合材料具有较好的冲击强度。纤维经表面处理后，其弯曲强度、弯曲模量、横向和纵向剪切强度均有不同程度的提高，冲击强度略有下降。随着纤维体积含量的增加，横向剪切强度增加，纵向剪切和弯曲强度增加到一定程度反而下降。吸湿平衡后的力学性能有所下降。     

Mathematical models of the thermal decomposition of coal: 6. Effect of blend composition on coke strength

A mathematical model to predict the strength of a coke manufactured from a blend of coals is proposed. The model operates in terms of ‘bond strengths’ between the constituents. The magnitudes of these bond strengths may be determined from the strengths of cokes manufactured from the individual constituents and from a limited number of binary blends. The model has been applied to predictions of the M₁₀ index of coke strength for binary and ternary blends, and the predictions are in reasonable agreement with the experimental data. In particular, the model is able to account for the behaviour of incompatible coals and bridging coals in blends.     

The effect of firing conditions on the Strength of Hematite compacts

The strengths of fired hematite compacts have been measured and the results correlated with changes in the other physical properties of the compacts brought about by the sintering treatments. The decrease in porosity during sintering was the main factor in strength development. Empirical equations were developed which predict the porosity and strength of the compacts as a function of the time/temperature treatments.Structural observations indicated that at high porosity values the fracture mode was intergranular, whereas at low porosities the mode was mainly transgranular. Regardless of the time/temperature treatments, the compact strengths tended towards a maximum limiting value.     

不同无机粒子对不饱和聚酯树脂浇注体强度的影响

本文选用400目磨碎玻纤粉、滑石粉及纳米二氧化硅(SiO2)作填料,研究了这些填料的加入对不饱和聚酯树脂浇注体弯曲强度及冲击强度的影响。结果表明,树脂中加入经偶联剂处理过的磨碎玻纤粉,随着填料含量的增加,其弯曲强度先下降而后增加,而冲击强度单调增加;当上述体系中再添加纳米SiO2后,除了冲击强度在纳米SiO2加入1%时略有增加外,其它的强度值均下降;和玻纤粉相比,当树脂中加入30%的滑石粉后,树脂浇注体的冲击强度比含30%玻纤粉的浇注体略有提高,但弯曲强度却略有降低。     

Investigation of texture effect on visual colour difference evaluation

The texture effect on visual colour difference evaluation was investigated in this study. Five colour centers were selected and textured colour pairs were generated using scanned textile woven fabrics and colour‐mapping technique. The textured and solid colour pairs were then displayed on a characterized cathode ray tube (CRT) monitor for colour difference evaluation. The colour difference values for the pairs with texture patterns are equal to 5.0 CIELAB units in lightness direction. The texture level was represented by the half‐width of histogram, which is called texture strength in this study. High correlation was found between texture strength and visual colour difference for textured colour pairs, which indicates that an increasing of 10 units of texture strength in luminance would cause a decreasing of 0.25 units visual difference for the five colour centers. The ratio of visual difference between textured and solid colour pairs also indicates a high parametric effect of texture. © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 341–347, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.     

Influence of silica fume on the tensile strength of concrete

The present paper is directed towards developing a better understanding on the isolated contribution of silica fume on the tensile strengths of high-performance concrete (HPC). Extensive experimentation was carried out over water-binder ratios ranging from 0.26 to 0.42 and silica fume-binder ratios from 0.0 to 0.3. For all the mixes, compressive, flexural and split tensile strengths were determined at 28 days. The compressive, as well as the tensile, strengths increased with silica fume incorporation, and the results indicate that the optimum replacement percentage is not a constant one but depends on the water-cementitious material (w/cm) ratio of the mix. Compared with split tensile strengths, flexural strengths have exhibited greater improvements. Based on the test results, relationships between the 28-day flexural and split tensile strengths with the compressive strength of silica fume concrete have been developed using statistical methods.