No abstract

Single-edge precracked-beam (SEPB) tests were performed on a commercial lead zirconate titanate (PZT) ceramic. Mechanical loading was applied by the crosshead displacement control of a screw-driven electromechanical test machine. The fracture toughness parameter K C was determined for various electric fields. A finite element analysis was also done to calculate the total potential energy release rate, mechanical strain energy release rate, and stress intensity factor for three-point flexure piezoceramic specimens with permeable and impermeable cracks under displacement and load control conditions. Numerical investigation and comparison with test data indicate that the energy release rate, upon application of the permeable model, is useful for predicting crack growth in PZT ceramic under electromechanical loading. Based on current findings, we suggest that the energy release rate criteria for the permeable crack are superior to fracture criteria for the impermeable crack.

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To estimate the electric fracture toughness, indentation fracture (IF) tests were made on piezoelectric materials under combined mechanical and electrical loads. Lead zirconate titanate (PZT) ceramics from a commercial source were used. A three-dimensional finite element analysis was also employed to calculate the energy release rate and stress intensity factor. Surface cracks produced by indentation with Vickers indented were modeled as two point-force loaded half-penny-shaped cracks.

Cryogenic interlaminar beam tests in the form of three-point flexure are examined both experimentally and analytically. The use of the short-beam shear test for measuring the interlaminar shear strength of glass-cloth/epoxy laminates at low temperatures is evaluated first. The interlaminar shear tests were carried out with short-beam shear specimens at room temperature, 77 K and 4 K to evaluate the interlaminar shear strength of G-10CR glass-cloth/epoxy laminates. Each specimen was placed on two roller supports that allow lateral motion and a load was applied directly at the center of the specimen. These tests were conducted in accordance with ASTM, 1984, “Standard Test Method for Apparent Interlaminar Shear Strength of Parallel Fiber Composites by Short-Beam Method,” Designation D2344-84. The effects of temperature, specimen width, and span-to-thickness ratio on the apparent interlaminar shear strength are shown graphically. Photomicrographs (scanning electron micrographs, optical micrographs) of actual failure modes were utilized to verify the failure mechanisms. A three-dimensional finite element analysis was also performed to investigate the effects of specimen width and span-to-thickness ratio on the shear stress distribution in the mid-plane. Effective elastic moduli were determined under the assumption of uniform strain inside the representative volume element. The numerical findings are then correlated with the experimental results.