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  • 1
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    Mechanical characterization of unnotched SCS6/Ti-15-3 metal matrix composites at room temperature (1990)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The Ti-15-3 metal matrix composites containing silicon-carbide (SCS6) fibers, in five different lay-ups, have been tested at room temperature to determine static strengths and mechanical properties. Experimental data and predicted values of the laminate properties and strengths showed good correlation. The off-axis laminate plies (that is, 90 and 45 deg) suffered fiber/matrix interface failures at stress levels as low as 20 ksi, thus significantly affecting the mechanical properties of the laminate. Edge replicas were used to verify the fiber/matrix separations. Microscopic examinations determined that the fiber/matrix failures were occurring in the titanium/silicon reaction layer. Fatigue tests were performed on unnotched specimens to determine the number of cycles to failure versus cyclic stress level. It was found that the stress in the 0 deg fiber could be used to correlate the fatigue life of different laminates containing 0 deg plies.
    Keywords: COMPOSITE MATERIALS
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    An analysis of fiber-matrix interface failure stresses for a range of ply stress states (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A graphite/bismaleimide laminate was prepared without the usual fiber treatment and was tested over a wide range of stress states to measure its ply cracking strength. These tests were conducted using off-axis flexure specimens and produced fiber-matrix interface failure data over a correspondingly wide range of interface stress states. The absence of fiber treatment, weakened the fiber-matrix interfaces and allowed these tests to be conducted at load levels that did not yield the matrix. An elastic micromechanics computer code was used to calculate the fiber-matrix interface stresses at failure. Two different fiber-array models (square and diamond) were used in these calculations to analyze the effects of fiber arrangement as well as stress state on the critical interface stresses at failure. This study showed that both fiber-array models were needed to analyze interface stresses over the range of stress states. A linear equation provided a close fit to these critical stress combinations and, thereby, provided a fiber-matrix interface failure criterion. These results suggest that prediction procedures for laminate ply cracking can be based on micromechanics stress analyses and appropriate fiber-matrix interface failure criteria. However, typical structural laminates may require elastoplastic stress analysis procedures that account for matrix yielding, especially for shear-dominated ply stress states.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-108999 , NAS 1.15:108999
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    NASA TECHNICAL REPORTS
  • 3
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    Deformations and strains in adhesive joints by moire interferometry (1984)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Displacement fields in a thick adherend lap joint and a cracked lap shear specimen were measured by high sensitivity moire interferometry. Contour maps of in-plane U and V displacements were obtained across adhesive and adherent surfaces. Loading sequences ranged from modest loads to near-failure loads. Quantitative results are given for displacements and certain strains in the adhesive and along the adhesive/adherend boundary lines. The results show nonlinear displacements and strains as a function of loads or stresses and they show viscoelastic or time-dependent response. Moire interferometry is an excellent method for experimental studies of adhesive joint performance. Subwavelength displacement resolution of a few micro-inches, and spatial resolution corresponding to 1600 fringes/inch (64 fringes/mm), were obtained in these studies. The whole-field contour maps offer insights not available from local measurements made by high sensitivity gages.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-CR-172474 , NAS 1.26:172474
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    NASA TECHNICAL REPORTS
  • 4
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    Loading rate sensitivity of open-hole composite specimens in compression (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The results are reported of an experimental study on the compressive, time-dependent behavior of graphite fiber reinforced polymer composite laminates with open holes. The effect of loading rate on compressive strength was determined for six material systems ranging from brittle epoxies to thermoplastics at both 75 F and 220 F. Specimens were loaded to failure using different loading rates. The slope of the strength versus elapsed time-to-failure curve was used to rank the materials' loading rate sensitivity. All of the materials had greater strength at 75 F than at 220 F. All the materials showed loading rate effects in the form of reduced failure strength for longer elapsed-time-to-failure. Loading rate sensitivity was less at 220 F than the same material at 70 F. However, C12000/ULTEM and IM7/8551-7 were more sensitive to loading rate than the other materials at 220 F. AS4/APC2 laminates with 24, 32, and 48 plies and 1/16 and 1/4 inch diameter holes were tested. The sensitivity to loading rate was less for either increasing number of plies or larger hole size. The failure of the specimens made from brittle resins was accompanied by extensive delaminations while the failure of the roughened systems was predominantly by shear crippling. Fewer delamination failures were observed at the higher temperature.
    Keywords: COMPOSITE MATERIALS
    Type: Symposium on Composite Materials: Testing and Design; Apr 27, 1988 - Apr 29, 1988; Sparks, NV; United States
    Format: text
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