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  • 1
    Electronic Resource
    Electronic Resource
    Force measurement using an ac atomic force microscope (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 4045-4052 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Complete amplitude-displacement-frequency spectra for a lever of an atomic force microscope have been measured and used to determine surface forces in air. Two ac techniques were used to measure the shift in resonant frequency of the Ni lever, as a function of separation from a mica surface. A strong, short-range force was observed for freshly prepared surfaces, implying a van der Waals interaction. A weak, long-range force was observed after exposure of the surfaces for some hours, suggestive of a capillary interaction. The long-range force appeared to contain a nonconservative element which increased on approach to the surface. The results have implications for surface-force determinations by single tip displacement scans, and for imaging with force microscopes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344961
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  • 2
    Electronic Resource
    Electronic Resource
    Fracture toughness measurements of YBa2Cu3Ox single crystals (1987)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 51 (1987), S. 454-456 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report fracture toughness measurements on single crystals of YBa2Cu3Ox, the phase responsible for superconductivity above liquid-nitrogen temperatures. Indentation crack length measurements on the (010) orthorhombic crystal growth faces revealed the (100) and (001) planes as preferred fracture planes. The toughness of these planes is Kc=1.1±0.3 MPa m1/2, and the hardness H=8.7±2.4 GPa. The observed growth of both radial and lateral cracks in ambient air suggests that these crystals are susceptible to moisture-enhanced nonequilibrium crack propagation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.98420
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  • 3
    Electronic Resource
    Electronic Resource
    Rapid measurement of static and dynamic surface forces (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 56 (1990), S. 2408-2410 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We present a technique for rapid measurement of surface forces using an ac force microscope. Measurement of both the amplitude and relative phase of a cantilever probe allows simultaneous and rapid determination of static and velocity-dependent forces of order nN over nm length scales. Using this technique, we have also demonstrated the high lateral spatial resolution of the force microscope in the measurement of surface forces.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102893
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  • 4
    Electronic Resource
    Electronic Resource
    Stress hysteresis during thermal cycling of plasma-enhanced chemical vapor deposited silicon oxide films (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 1988-1992 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The mechanical response of plasma-enhanced chemical vapor deposited SiO2 to thermal cycling is examined by substrate curvature measurement and depth-sensing indentation. Film properties of deposition stress and stress hysteresis that accompanied thermal cycling are elucidated, as well as modulus, hardness, and coefficient of thermal expansion. Thermal cycling is shown to result in major plastic deformation of the film and a switch from a compressive to a tensile state of stress; both athermal and thermal components of the net stress alter in different ways during cycling. A mechanism of hydrogen incorporation and release from as-deposited silanol groups is proposed that accounts for the change in film properties and state of stress. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1432773
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  • 5
    Electronic Resource
    Electronic Resource
    Influence of crack velocity thresholds on stabilized nonequilibrium fracture (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1902-1910 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The time dependence for crack extension in stabilizing mechanical energy release rate fields has been analyzed, including the thermodynamic threshold for crack motion. Analyses based on crack velocity relations ignoring the threshold predict cessation of crack motion only at infinite crack lengths, in clear contrast to experimental observations. The new analysis predicts that crack motion will cease at finite crack lengths, in accord with experimental results, and includes the zero threshold result as an asymptotic limit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342902
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  • 6
    Electronic Resource
    Electronic Resource
    Toughening of a Cordierite Glass–Ceramic by Compressive Surface Layers (2005)
    Oxford, UK : Blackwell Science Inc
    Journal of the American Ceramic Society 88 (2005), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An indentation fracture mechanics analysis is developed to characterize the toughening effects of a compressive surface layer in brittle materials. The analysis is used to describe the enhanced toughness of cordierite glass–ceramic laminate composites, in which thermal-expansion mismatch effects induced uniform stress in the exterior layers of the symmetric exterior:interior:exterior structures. Interpretation of indentation crack length and inert strength tests via the analysis shows that cracks can be viewed as experiencing discrete regions of decreasing stabilization on propagation from small cracks and complete containment within the compressive layer to large cracks and partial extension into the compensating tensile interior. The observations are described using a stress-intensity factor for circular cracks in linear stress fields that includes different base and surface values for extended cracks. Deconvolution of inert strength data for the model cordierite system studied suggested an increase in toughness from 1.4 MPa·m1/2 for the base material to a peak of about 5 MPa·m1/2 for a 1:18:1 composite structure, with attendant increases in strength and flaw tolerance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00285.x
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  • 7
    Electronic Resource
    Electronic Resource
    Toughening of an Alumina—Mullite Composite by Unbroken Bridging Elements (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The toughness-curve (T-curve) behavior of a composite that is composed of 30 vol% spherical, polycrystalline, fine-grained alumina agglomerates dispersed throughout a constant-toughness 50-vol%-alumina—50-vol%-mullite matrix was compared to that for a coarse-grained agglomerate version of the composite, with the intent of identifying the operative toughening mechanisms in the latter. The T-curve behavior was evaluated using the indentation-strength method, and the underlying T-curves were deconvoluted from experimental data using an indentation-fracture-mechanics model. Compared to the T-curve of the coarse-grained composite, the toughness of the “fine-grained” composite increased from a similar initial toughness and over a similar crack-length range but to a lower saturation value. The T-curve of the fine-grained composite can be explained as being derived predominantly from unbroken bridging elements in the crack wake, set up by agglomerate-induced crack-path deflections in the matrix. This mechanism is proposed to function to the same degree and account for the majority of the observed toughening in the coarse-grained composite, with the remaining toughening increment being derived from intra-agglomerate grain bridging. Calculations suggest that unbroken bridging elements do not behave as simple elastic cantilevered beams that bend uniaxially with increasing crack-opening displacement.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01282.x
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  • 8
    Electronic Resource
    Electronic Resource
    In Situ Cube-Corner Indentation of Soda–Lime Glass and Fused Silica (2004)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 87 (2004), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Indentation fracture with a cube-corner diamond pyramid on soda–lime silicate glass and fused silica is investigated during the entire indentation cycle in both silicone oil and ambient-air environments. Radial cracks form immediately on loading in all cases. The two-component, elastic-contact + elastic-plastic mismatch (residual) stress field model that has been used successfully to describe radial crack evolution at Vickers indentations fails to describe the fracture response with the cube-corner. The amplitudes of both elastic-contact and residual stress-intensity factors as deduced from these cube-corner experiments are up to a factor of 10 greater than have been previously observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1551-2916.2004.01494.x
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  • 9
    Electronic Resource
    Electronic Resource
    Alumina Agglomerate Effects on Toughness-Curve Behavior of Alumina–Mullite Composites (2000)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 83 (2000), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Toughness-curve (T-curve) behavior of composites of spherical, polycrystalline, coarse-grained, alumina agglomerates dispersed throughout a constant-toughness, fine-grained, 50–50 vol% alumina–mullite matrix has been evaluated as a function of agglomerate content for the range 15 to 45 vol%. T-curve behavior was evaluated using the indentation-strength method. Increasing alumina agglomerate content resulted in a progressive increase of large indentation load strengths with negligible change of plateau strength levels at small indentation loads. This behavior is consistent with underlying T-curves that rise to greater values and are shifted toward longer crack lengths with increasing agglomerate content, suggesting that both bridge spacing and bridge potency increase with increasing agglomerate content over the range tested. The proposed relationships between bridge spacing and agglomerate content, and bridge potency and agglomerate content, are rationalized in terms of residual stress considerations. The indentation-strength data also demonstrated that the composite containing the greatest alumina agglomerate content, 45 vol%, exhibited the greatest flaw tolerance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.2000.tb01687.x
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  • 10
    Electronic Resource
    Electronic Resource
    Toughness-Curve Behavior of an Alumina-Mullite Composite (1998)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 81 (1998), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Toughness-curve (T- or R-curve) behavior of a composite of 30 vol%, polycrystalline, coarse-grained, spherical alumina agglomerates dispersed throughout a fine-grained, 50/50 vol% alumina-mullite matrix, and that of its microstructural end-members (100% matrix and 100% alumina), were studied using the indentation-strength-in-bending technique. T-curves were deconvoluted from indentation-strength data using an indentation fracture mechanics model. The monolithic matrix and alumina exhibited an invariant toughness and a moderate T-curve, respectively. In comparison, the composite exhibited a pronounced T-curve. The T-curve of the composite is best explained as deriving from the interaction of a propagating crack with the alumina agglomerates: crack propagation experiments revealing two possible toughening mechanisms-intra-agglomerate frictional grain bridging and elastic bridging ligaments in the matrix that appeared to be associated with alumina agglomerates. Rule-of-mixtures toughness calculations indicated that intra-agglomerate bridges could account for only a fraction of the toughening exhibited by the composite. It is suggested that the extra toughening arises from the elastic bridging ligaments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1998.tb02668.x
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