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  • 1
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    Fracture toughness of boron/aluminum laminates with various proportions of 0 deg and plus or minus 45 deg (1980)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The fracture toughness of boron/aluminum laminates was measured on sheet specimens containing central slits of various lengths that represent cracks. The specimens were loaded axially and had various widths. The sheets were made with five laminate orientation. Fracture toughness was calculated for each laminate orientation. Specimens began failing at the ends of the slit with what appeared to be tensile failures of fibers in the primary load carrying laminae. A general fracture toughness parameter independent of laminate orientation was derived on the basis of fiber failure in the principal load carrying laminae. The value of this parameter was proportional to the critical value of the stress intensity factor. The constant of proportionality depended only on the elastic constants of the laminates.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TP-1707 , L-13880
    Format: application/pdf
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  • 2
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    Tensile stress-strain behavior of boron/aluminum laminates (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The tensile stress-strain behavior of five types of boron/aluminum laminates was investigated. Longitudinal and transverse stress-strain curves were obtained for monotonic loading to failure and for three cycles of loading to successively higher load levels. The laminate strengths predicted by assuming that the zero deg plies failed first correlated well with the experimental results. The stress-strain curves for all the boron/aluminum laminates were nonlinear except at very small strains. Within the small linear regions, elastic constants calculated from laminate theory corresponded to those obtained experimentally to within 10 to 20 percent. A limited amount of cyclic loading did not affect the ultimate strength and strain for the boron/aluminum laminates. The laminates, however, exhibited a permanent strain on unloading. The Ramberg-Osgood equation was fitted to the stress-strain curves to obtain average curves for the various laminates.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TP-1117 , L-11864
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  • 3
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    Fatigue-crack initiation and growth in notched 2024-T3 specimens monitored by a video tape system (1976)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Fatigue-crack initiation and early stages of growth in notched 2024-T3 aluminum alloy sheet specimens were monitored during constant-amplitude fatigue tests conducted for a range of stress ratios. A video tape system was developed to detect fatigue cracks 0.1 mm in length on the sheet surface and to monitor their growth. Fatigue cracks initiated either at the notch corner or on the notch surface. Most of the first fatigue cracks started as notch-corner cracks, and the crack-initiation period was defined as the number of cycles for which the crack was 0.1 mm in length on the sheet surface. For each of the stress ratios used, the results showed that at the low stress levels, the crack-initiation period constituted at least 90 percent of the fatigue lives. However, for the negative stress ratios at the high stress levels, cracks started as early as at about 40 percent of the fatigue lives.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-8224 , L-10754
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  • 4
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    A method for determining local elastoplastic stress and strain in metallurgically bonded notched laminates subjected to a loading cycle (1974)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A semianalytical method was developed for determining elastoplastic cyclic stresses and strains at notch roots in metallurgically bonded metal laminates. The method is based on the Neuber equation, which was used with an effective stress-strain curve for the laminate. It was applied to laminates containing a circular hole which were subjected to one cycle of reversed loading. The laminates consisted of two elasto-perfectly-plastic materials with different yield strengths and with either equal or different Young's moduli. A laminate of high-strength titanium alloy with alternate layers of commercially pure titanium was also analyzed. The accuracy of the method was evaluated by comparing the stresses and strains with those calculated from a finite-element analysis. The results estimated by the simple method based on the Neuber equation agreed closely with the results computed from the more elaborate finite-element analysis.
    Keywords: STRUCTURAL MECHANICS
    Type: NASA-TN-D-7766 , L-9753
    Format: application/pdf
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