Face/Core Debonding Characterization of Foam and Honeycomb Core Sandwich Structures Using Single Cantilever Beam Testing Method

Single Cantilever Beam (SCB) testing was conducted on foam and honeycomb core sandwich specimens to predict the fracture toughness and bonding strength. Adhesion characteristics can also be identified between facesheet and core materials conducting SCB test on precracked specimen. Disbonding under combined tensile and shear loading may involve failure modes such as kinking and cell buckling. Modified Beam Theory (MBT) method specifies required parameters to generate a least square plot based on experimentally determined compliance and disbond length obtained during the SCB test. Interfacial fracture toughness Gc, enumerated by following recommended data reduction methodologies, required to predict minimum Gc to initiate disbond growth. Finally, experimental compliance was compared with elastic foundation stiffness compliance to verify the performance of the test. Good agreement between two compliance solutions validates the accuracy of the SCB test.

Bond Joint Analysis of Thermoplastic Composite Made from Stacked Tailored Blanks

The interlaminar properties of a bond joint of stacked layers in a carbon fibre-reinforced composite with a thermoplastic matrix were evaluated under static loading. The un-precracked tension specimen with an external reinforcing layer was analysed in detail in the area of a bond joint. A detailed finite element method (FEM) analysis was performed to evaluate the influence of the bond joint shape on the interlaminar cohesive forces, which are simulated using the cohesive zone model (CZM). Simple lap and tapered joints were analysed. Continuum and shell elements were utilized in the FEM analysis, and the delamination results obtained using both solutions were compared to each other; however, no significant influence of the bond joint shape on the delamination onset was observed. The FEM analysis was supported using an experimental test on an un-precracked specimen made from prepreg with a carbon fibre fabric and a polyphenylene sulphide (PPS) matrix.

Micromechanical Analysis of Constraint Effect on Fracture Initiation in Strength Mismatched Welded Joints

In this paper the micromechanical approach to ductile fracture was applied in a study of constraint effect on crack growth initiation in mismatched welded joints. The single-edged notched bend specimens (precrack length a0/W=0.32) were experimentally and numerically analyzed. The coupled micromechanical model proposed by Gurson, Tvergaard and Needleman was used. Constraint effect was tested by varying widths of the welded joints (6, 12 and 18mm). Highstrength low-alloyed (HSLA) steel was used as the base metal in a quenched and tempered condition. The flux-cored arc-welding process in shielding gas was used. Two different fillers were selected to obtain over- and undermatched weld metal. The micromechanical parameters used in prediction of the crack growth initiation on precracked specimen were calibrated on a round smooth specimen. The difference in fracture behavior between over- and undermatched welded joints obtained in experimental results was followed by numerical computations of void volume fraction in front of the crack tip.

Development of Experimental Procedure Based on the Load Separation Method to Measure the Fracture Toughness of Zr-2.5Nb Tubes

The load separation method was employed to measure the pl η -factor, the growing crack length and the applied J-integral during the course of the test of small curved CT specimen of Z-2.5Nb pressure tube material. The effect of the notch tip radius of the notched (reference) CT specimen on the separation parameter was analyzed to predict the crack growing length in the precracked specimen. To avoid the effect of load relaxation in the reference specimen on the separation parameter and the crack growing length estimation, the load was assumed to be maximum and constant value behind the peak load in the reference curve.

Toughness Assessment of a Variety of Materials: Similarities and Discrepancies

To determine the toughness of materials, Charpy V notch test has been widely utilized over the world. This method is easy to conduct, but obtained values are some what qualitative. Instrumented test has also a long history and gives us a loading history during impact. However this method is also still remaining in the range of a screening test. The author has successfully developed CAI (Computer Aided Instrumented Impact Testing) System for the evaluation of dynamic fracture toughness. In this CAI system, dynamic fracture toughness parameters such as Kd, Jd, Tmat and various absorbed energies can be obtained from the load-deflection curve of a single precracked specimen for both ductile and brittle materials