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  • 1
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An experimental procedure is presented which allows the direct visual observation and measurement of crack extension in ceramic materials at high temperatures. The directly measured crack lengths, gained from displacement-controlled three-point bend tests, are compared to those calculated from the compliance. An energy approach is presented to calculateR-values from the load-displacement curves. TheseR-values for a pure alumina and an alumina containing a glassy phase, for which the load-displacement curves show non-linearity at high temperatures, are compared toK-values andJ-values. The stress intensity approach, based on traction-free surfaces, gives unrealistic data for the nonlinear behaving material owing to adhesive effects behind the actual crack front. TheJ-values, calculated by two methods developed for investigations with moving cracks, are identical to those from the energy approach.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 21 (1986), S. 411-418 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Ceramic three-point bend specimens were pre-cracked in a displacement-controlled test in air at room temperature to form sharp cracks of different lengths. Critical stress intensity factors (K IC were then measured as a function of sharp crack length in a fast-fracture, load-controlled test. Crack resistance curves (K IC against crack length) were determined for three commercially pure aluminas of different grain size, a debased alumina containing a glassy phase, and a partially stabilized zirconia (PSZ) material. The crack resistance curves proved to be flat for the finer-grained and the debased alumina. A steeply rising crack resistance curve was, however, observed for a pure coarse-grained alumina material which is explained by friction effects of the cracked microstructure behind the measured crack front. The effect is influenced by the test procedure itself. Though crack branching takes place the crack resistance curve of PSZ is completely flat, which is attributed to fast fracture testing where only the most dangerous flaw is activated.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 22 (1987), S. 1352-1358 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Ceramic three-point bend specimens were pre-cracked in a displacement-controlled test in air at room temperature to form sharp cracks of different lengths. Critical stress intensity factors (K lc) were then measured as a function of sharp crack length in a fast-fracture, load-controlled test at 900, 1000 and 1100° C. By means of these fast fracture tests, crack resistance curves (K lc against crack length) were determined for two commercially pure aluminas of different grain size and for a debased alumina containing a glassy phase. The crack resistance curve for the pure, fine grained alumina proved to be flat at 900° C, as was found for room temperature. A steeply rising crack resistance was, however, observed for the pure coarse-grained alumina at 1100° C and for the debased alumina at 1000 and 1100° C. This rise in KR curves is explained by friction effects of the cracked microstructure behind the crack front for the coarse grained alumina and by adhesive forces caused by the second phase behind the crack front for the debased alumina. These facts are proved by comparison to experiments on notched specimen and by annealing experiments. From the annealing experiments the size of the adhesive zone is estimated for the debased material.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 16 (1981), S. 836-838 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 15 (1980), S. 188-196 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A study is reported of the fracture mechanics of metal-to-ceramic laminates (Al2O3/Nb, Si3N4/Zr) produced by solid-state bonding. The bond quality of notched bend and tension specimens is described in terms of a stress intensity factor K ICV, which is evaluated in the same way as for isotropic material. K ICV is measured as functions of the microstructure of the constituents, the metal layer thickness, the environmental conditions and the test temperature. At very high test temperatures where plastic flow occurs, the J-integral was used for bond quality characterization. For the linear elastic case, the J-value is compared with the stress intensity concept K ICV. In contrast to the behaviour of a bulk ceramic material, the J-value increases with increasing test temperature if a thick metal layer (3 mm) is used.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 15 (1980), S. 2861-2866 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Studies on the subcritical crack growth behaviour of partially stabilized zirconia (ZrO2-I, 5 to 10 vol% tetragonal phase; ZrO2-II, 35%) were carried out using the double-torsion technique and data from the dynamic fatigue of unnotched bend specimens. The results of subcritical crack growth support the model of stress induced transformation from the tetragonal to monoclinic modification. Differences in the crack growth parameter “n” (as-received condition) using the double-torsion technique or bend specimens may be explained by the special nature of subcritical crack extension at stressed surfaces for these different specimen types. The log v-log K i plot of ZrO2-I using the double torsion technique shows a plateau of constant velocity, which has to be attributed to a tetragonal-monoclinic transformation. After annealing (1500° C, 5 h) the plateau has vanished and the n value is comparable to bend test in an as-received condition.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 16 (1981), S. 836-838 
    ISSN: 1573-4803
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of materials science 3 (1984), S. 997-999 
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 12 (1981), S. 167-174 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: Fracture Toughness Determination of Alumina and Cemented Carbide with Different Testing MethodsFracture toughness of a sintered alumina and two tungsten carbidecobalt materials was determined using four-point-bend specimens with straight through and chevron notches and with the short rod specimen. With the specimens with a straight through notch a lower KIc was measured for Al2O3 and a higher for WC-Co compared to the chevron-notched specimens. This behavior was explained by the different shapes of the crack growth resistance curves and the different critical notch radii. For Al2O3 a steeply rising crack growth resistance curve was measured in a controlled fracture test, for WC-Co a flatter curve was obtained. The effect of the shape of the crack growth resistance curve and of notch width on the evaluated toughness is discussed.
    Notes: An einem gesinterten Aluminiumoxid und zwei WC-Co-Hartmetallen wurde der Bruchwiderstand im Vierpunkt-Biegeversuch mit Flachkerben und Spitzkerben sowie mit der kurzen Rundprobe mit Spitzkerbe bestimmt. Bei Al2O3 ergab sich mit den Flachkerbproben ein kleinerer Wert als mit den Spitzkerbproben, bei WC-Co war es umgekehrt. Dieses Verhalten wurde auf die unterschiedliche Form der Rißwiderstandskurve und die unterschiedliche Größe der kritischen Kerbradien zurückgeführt. Bei Al2O3 wurde im kontrollierten Bruchversuch eine stark ansteigende, bei WC-Co eine flache Rißwiderstandskurve gemessen. Der Einfluß der Form der Rißwiderstandskurve und der Kerbbreite auf die ermittelten Kennwerte wird diskutiert.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Materialwissenschaft und Werkstofftechnik 13 (1982), S. 254-258 
    ISSN: 0933-5137
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Description / Table of Contents: A Modified Weibull Statistics of Ceramic KIC DataAn explanation is given for the standard deviation of KIC-data and for the dependence of KIC values measured with ceramic materials on the specimen volume (specimen thickness). The probability distribution of measured KIC-data is described by a modified Weibull theory. The theory is verified by experimental data using specimens with different thickness and a through the thickness notch. The experimental results are in good agreement with the theory.
    Notes: Es wird eine Erklärung für die in der Praxis auftretenden Streuungen experimentell an Keramiken gewonnener KIC-Daten und deren Abhängigkeit vom Probenvolumen (Probenbreite) angegeben. Weiter wird die Wahrscheinlichkeitsverteilung empirischer KIC-Werte mit einem der Weibulltheorie analogen Modell quantitativ beschrieben und dieses Modell experimentell überprüft. Gute Übereinstimmung zwischen Theorie und Experiment wird gefunden.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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