This study examined fracture toughness (KIc) measurements obtained using the indentation fracture (IF) method with a view to improving their reliability.The KIc values of five dental ceramics were measured using the IF method with five different formulas, and the single-edge precracked beam (SEPB) method was used as a control. The elastic moduli of the dental ceramics were evaluated by dynamic hardness test. Load conditions of the dental ceramics that produced a median/radial crack for the IF method formulas were investigated.Based on the resultant c/a and P/c1.5 values, the indentation load (P) required for median/radial crack occurrence varied greatly from 29.4 to 196 N depending on the ceramic used. Among the five formulas, none of the KIc values obtained by the IF method with Miyoshi's formula differed significantly (p >0.05) from the values obtained using SEPB method.These results suggested that, after an appropriate indentation load is determined, reliable KIc values for small dental ceramic specimens can be easily obtained using the IF method if Miyoshi's formula is used in combination with the dynamic hardness test.
Grid-purlin system composed of RHS members are known to be effective to prevent buckling of the welded beams. In this paper, lattice dome composed of radial beams and welded grid purlins (Grid purlin shell dome) are studied. The linear, elastic, and elasto-plastic buckling strength of Grid purlin shell domes are analyzed using detailed FEM analyses. Their results are compared with the shell theory with continuum analogy and easy design approaches are investigated.
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