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  • 1
    Electronic Resource
    Electronic Resource
    Mechanisms for rate effects on interlaminar fracture toughness of carbon/epoxy and carbon/PEEK composites (1989)
    Springer
    Journal of materials science 24 (1989), S. 3387-3398 
    Details
    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 The objective of this study was to investigate strain-rate dependent energy absorption mechanisms during interlaminar fracture of thermosetting (epoxy) and thermoplastic (PEEK) uni directional carbon fibre (CF) composites. A simple model addressing the translation of matrix toughness to mode I and mode II interlaminar toughness of the composite is presented, in conjunction with a fractographic examination of the fracture surfaces and the fracture process. The observed rate dependency of composite fracture toughness is attributed to the rate dependent toughness of the viscoelastic matrix and the size of the process zone around the crack tip. Other important factors identified are the roughness of the fracture surface and fibre bridging.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01139070
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  • 2
    Electronic Resource
    Electronic Resource
    On the use of nanoscale indentation with the AFM in the identification of phases in blends of linear low density polyethylene and high density polyethylene (2000)
    Springer
    Journal of materials science 35 (2000), S. 221-228 
    Details
    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 The microstructures generated by blends of linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) following isothermal crystallization from the melt have been studied using several techniques. The traditional methods of electron microscopy, wide angle X-ray scattering, and differential scanning calorimetry were used to examine the superstructures, lattice spacings, and thermal properties, respectively. In addition, nanoindentation of specific moieties within the microstructure was performed using the atomic force microscope (AFM). The indentation measurements were used to generate values for the relative elastic moduli of the crystalline features and to identify phases within the superstructures. The AFM results were compared to results obtained from the aforementioned techniques and to microhardness measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1004781725300
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  • 3
    Electronic Resource
    Electronic Resource
    Relating elastic modulus to indentation response using atomic force microscopy (1997)
    Springer
    Journal of materials science 16 (1997), S. 117-119 
    Details
    ISSN: 1573-4811
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Abstracts are not published in this journal
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018533708655
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  • 4
    Electronic Resource
    Electronic Resource
    Numerical and experimental evaluation of the Mode III interlaminar fracture toughness of composite materials (1989)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 10 (1989), S. 293-304 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: The Crack Rail Shear (CRS) specimen is a proposed test method to characterize the interlaminar Mode III critical strain energy release rate (GIIIc) of continuous fiber-reinforced composite materials. The specimen utilizes the two rail shear test fixture and contains embedded Kapton film between designated plies to provide a starter crack for subsequent fracture testing. Analytical expressions for specimen compliance and GIII are based upon Strength of Materials (SM) principles. The model identifies important material and geometric parameters and provides a simple data reduction scheme. A quasi-three-dimensional, linear elastic finite element stress analysis verifies the purity of the Mode III fracture state and identifies admissible crack lengths to be used in the experimental study. A fully three-dimensional linear elastic finite element analysis of the CRS is employed to investigate the influence of edge effects on the fracture state for the finite length sample. Results based upon a uniform crack extension indicate a small region of mixed mode behavior at traction free edges which decay to a pure Model III fracture state in the interior of the sample. Furthermore, the GIII distribution along the crack front decreases at the free edges from a maximum plateau region in the interior. The three-dimensional analysis allows edge effects to be minimized by selecting appropriate specimen lengths. Compliance and strain energy release rates are in good agreement with the SM model. An experimental program was performed to measure GIIIc of two graphite epoxy systems. GIIIc results for AS4/3501-6 were found to be 1.6 times the Mode II fracture toughness, while IM7/8551-7 exhibited equivalent Mode II and Mode III fracture toughnesses. Mode III fracture surfaces revealed microstructural deformations characteristic of Mode II fracture.
    Additional Material: 18 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750100505
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  • 5
    Electronic Resource
    Electronic Resource
    Analytical solutions for fiber orientation in 2-D flows of dilute suspensions (1990)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 11 (1990), S. 56-64 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Analytical solutions for fiber orientation in dilute solutions are presented for both 2-D planar and axisymmetric flow. The viscosity is assumed to be independent of position along the flow direction, but varies through the thickness of the mold cavity. For the particular case of a laminate of two fluids, an analytical solution is derived. Based upon the assumption that the fluid adjacent to the mold wall exhibits reduced viscosity due to non-isothermal considerations, the fluid kinematics simplify, and an analytical solution to Jeffery's orientation equation is derived. Since the fiber orientation analysis is based on Jeffery's equation, it is valid only for dilute suspensions, i.e. for fiber volume fraction 〈 1/(fiber aspect ratio)2. Qualitatively, the analytical results obtained provide superior correlation with experimental results, indicating that non-isothermal fluid flow may play an important role in the development of the fiber orientation distribution in the molded component.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750110108
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  • 6
    Electronic Resource
    Electronic Resource
    Weld line studies on transfer-molded thermosetting composite materials (1989)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 10 (1989), S. 184-193 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Multiple gating and the presence of inserts make weld lines (also known as knit lines) almost unavoidable in commercially produced moldings. These weld regions may be significantly weaker in strength than the bulk material away from the weld line. Hence, a molded section containing a weld line will only be as strong as the weld line, no matter how strong the surrounding bulk material. The influence of processing history on weld line performance is essential to optimally designed transfer-molded composite products with discontinuous-fiber-reinforced molding materials. This study has therefore been directed toward experimentally characterizing the weld line strength of a bulk molding compund (BMC) and a thick molding compound (TMC) as a function of the mold temperature, fill time/fill rate, and the postbake operation.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750100306
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  • 7
    Electronic Resource
    Electronic Resource
    The effect of isothermal aging on transverse crack development in carbon fiber reinforced cross-ply laminates (1995)
    Brookfield, Conn. : Wiley-Blackwell
    Polymer Composites 16 (1995), S. 154-160 
    Details
    ISSN: 0272-8397
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: An investigation into the effect of isothermal aging on the development of transverse cracks in cross-ply laminates of two high temperature composite systems was performed. The composite materials investigated were BASF X5260/640-800 and DuPont Avimid K/IM6. Changes in the glass transition temperature, composite weight loss, crack density, and mode I intralaminar fracture toughness were monitored during isothermal aging in air at 177°C for up to 2232 h. The two laminate configurations used in this study include two variations of the generic cross-ply configuration [02/90n]s, in which n equals 1 and 2. The results of this investigation show that a layer of degraded material forms at the surface of the X5260/640-800 bismaleimide laminates and that the thickness of the degraded layer increases with aging time. After 744 h of aging, transverse cracks form in the surface plies and an increasing crack density evolves as aging time is increased; however, transverse cracks do not form in the inner 90° ply groups with aging during the time period investigated. The Avimid K/IM6 thermoplastic polyimide laminates, which show evidence of cracking prior to aging, do not exhibit any significant change in crack density with aging. The results of the aging experiments also show that the bismaleimide system exhibits a weight loss of 1.5% and an increase in glass transition temperature from 250°C to 300°C after 2232 h of aging at 177°C, while the thermoplastic polyimide system shows a weight loss of only 0.05% and an increase in glass transition temperature from 280 to 285°C after 2232 h. Changes in the resistance to crack formation are also seen in these materials during aging. The mode I intralaminar fracture toughness, a measure of resistance to transverse crack formation, shows a 50% decrease after aging for 2232 h for the bismaleimide system, while the behavior exhibited by the thermoplastic polyimide shows little evidence of a reduction.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pc.750160207
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  • 8
    Electronic Resource
    Electronic Resource
    On the effect of nonhomogeneous flow fields on the orientation distribution and rheology of fiber suspensions (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 161-171 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The influence of nonhomogeneous flow fields on the orientation distribution and rheology of fiber suspensions is investigated. The Stokes-Burger model is used to approximate the forces and moments on the fiber for the subsequent calculation of fiber angular velocities for nonhomogeneous cases where the velocity gradients vary over the fiber length. For simple shear flows, an analytical solution based on the Stokes-Burgers model is derived. Fiber angular velocities are compared to previously published results. An iterative numerical technique is developed to calculate the otherwise indeterminate fiber angular velocities for other nonhomogeneous flows, such as non-isothermal Hele-Shaw flows. The value of shear is derived for which the angular motion of the fiber in a quadratic velocity field is identical to that in a linear shear flow. Subsequently, numerical solutions for orientation distribution functions are presented for cases where analytical solutions for distribution functions are not obtainable. The rheological properties are then studied, using the orientation tensor description, for nonhomogeneous flow fields where the fiber motion can be approximated by that in a shear flow, the equivalent shear rate obtained from the numerical scheme.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760310304
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  • 9
    Electronic Resource
    Electronic Resource
    A non-isothermal healing model for strength and toughness of fusion bonded joints of amorphous thermoplastics (1991)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 31 (1991), S. 1720-1730 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A study to investigate the influence of processing on the fusion bonding of graphite (AS4) poly(etheretherketone) (PEEK) thermoplastic composites (BASF commingled PEEK/graphite NCS woven fabric) using a polyetherimide (PEI) film at the interface is presented. Fundamental to all fusion bonding processes is the intermolecular diffusion between surfaces in intimate contact. A model based on the healing theory of amorphous polymers has been proposed to predict strength and toughness as a function of non-isothermal process history. This model considers two different microscopic failure mechanisms of a healed interface. For the first time, using non-isothermal data and proper data reduction procedures, it is possible to differentiate between these two mechanisms, which are otherwise indistinguishable from isothermal data. Temperature dependent reptation times representative of the kinetics of chain diffusion in the polymer have been evaluated for both mechanisms over a large range of process temperatures using fracture tests conducted on lap shear specimens manufactured using a hot press. Three alternate and independent techniques to estimate the reptation time in PEI indicate that the model based on the average interpenetration distance is most representative of the physical system. Lap shear strength predictions based on this formulation have been generated for various non-isothermal conditions measured in the hot press and are within 20% of the experimental data. The model was used to show that in isothermal processes, maximum strength and toughness can be achieved in less than 1 s for temperatures exceeding 290°C. Application of the model to a highly non-isothermal technique such as resistance welding using amorphous film technology is also presented. Model predictions show that asymptotic strength may be achieved in relatively short process times with appropriate welding conditions.
    Additional Material: 17 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760312406
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  • 10
    Electronic Resource
    Electronic Resource
    The influence of inclusion geometry on the elastic properties of discontinuous fiber composites (1994)
    Stamford, Conn. [u.a.] : Wiley-Blackwell
    Polymer Engineering and Science 34 (1994), S. 352-360 
    Details
    ISSN: 0032-3888
    Keywords: Chemistry ; Chemical Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Simplifying assumptions are used to reduce micromechanical treatments to compact expressions which directly reveal the role of the inclusion shape and aspect ratio in establishing the elastic behavior of heterogeneous materials. Attention is directed to the comparison of aligned ellipsoidal and cylindrical inclusions that exhibit transversely isotropic behavior characterized by five independent elastic constants. These comparisons show that the effective transverse in-plane moduli (ET*, k* and GTT*) are essentially independent of inclusion shape for aspect ratio greater than ∼ 20; ellipsoidal inclusions provide higher longitudinal reinforcement than cylindrical inclusions of equivalent aspect ratio. Comparison of predictions with measured elastic moduli shows that both the cylindrical and ellipsoidal shape models for isolated inclusions overpredict longitudinal elastic constants for systems which exhibit evidence of inclusion agglomeration. The notion of an effective aspect ratio based on clusters of filaments responding as a coherent unit appears to provide a means for reconciling a wide range of experimental observations.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/pen.760340417
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