A simple procedure was developed in order to estimate dynamic stress intensity factors under impact loading. The dynamic stress intensity factors were computed by superposing step response functions for crack-tips subjected to stress wave loading. The step response function was evaluated from the ratio of the dynamic crack opening displacement to the static one calculated by the same finite element model. The accuracy of this procedure was verified from the comparison of numerical results with analytical ones. The impact fracture experiments using circumferentially-notched round bar and center-notched disk specimens were performed and simulated to estimate the dynamic stress intensity factors. The onset of dynamic fracture was detected using the strain gage near the crack-tip. The dynamic fracture initiation toughness was measured at stress intensity factor rates of 105 to 106 MPa√ｍ/s. The experimental results were presented to elucidate the influence of loading rate on the pure mode If racture toughness for metallic alloys, metal-matrix composites, ceramics and glasses. Using center-notched and pre-cracked disk specimens, the impact fracture test method in diametralcompression was developed to measure the dynamic fracture toughness under combined mode I/II loading conditions. Some experimental results were presented to discuss the influence of mixed-mode loading and guidelines for the accurate evaluation of dynamic fracture strength of materials under impact loading.
The tensile strength of adhesive butt joints at high rates of loading is determined with a modified split Hopkinson bar using a cylindrical specimen. A commercially available cyanoacrylate adhesive (commonly termed an instantaneous adhesive) is tested. Two different adherend materials or bearing steel and high-strength aluminum alloy are used in the adhesion tests. Comparative tension tests at low and intermediate rates of loading are conducted in an Instron testing machine. An axisymmetric finite element analysis is performed to examine the stress distributions in the adhesive layer of adhesive butt joints in tension. The effects of loading rate, adherend materials and thickness of adhesive layer on the tensile strength of adhesive butt joints are examined in detail. It is shown that the joint tensile strength increases significantly with increasing loading rate and is greatly affected by both the adhesive layer thickness and adherend materials.
To characterize impact strength of fiber-reinforced ceramic composite, a modified split-Hopkinson bar method for the three point bending test has been introduced. Well ramped incident stress wave is essential to suppress the high frequency load fluctuation which usually veils the deformation characteristics of brittle materials in this kind of impact bending. Rate dependence of tensile and shearing fracture strength is shown and is fully discussed.
The NiTi base intermetallic compound and the platinum group metallic base superalloys were developed as the replacement of Ni-base superalloys for the disk and blade materials in gas turbine. The former alloys composed of B2 and β' phase with the coherent interface were designed to substitute Ti in NiTi by AL The proof stress showed the peak at 13. 9 at% Al in compression, while at 4. 4 at% in tension. The fracture toughness was about 40 MPa m1/2 for 4. 4 at% Al, over which amount decreased to be constant at about 5 MPa m1/2. In the latter alloys, Ir-X binary alloys, composed of fcc and Ll2 phases with coherent interface, were designed. At the temperature range from room temperature to 1800°C, Ir-15 at% Nb and Ir-15 at% Ta alloys showed the highest proof stress compared with the present industrial alloys. Ir-15 at% Nb alloy was the highest strength for Nb amount between O and 25 at%.
Titanium alloy is the one of indispensable materials for aircraft structure, because of its low density, high strength, good heat resistance and good corrosion resistance. But the weight ratio of titanium alloys for aircraft structure is not so high, especially commercial aircraft. That main reason is high production cost depends on high material and processing cost. So many material and airflame manufacturer have been developed low cost material and process. This paper describes the recent trend of low cost technology that include our study