Characterization of Dynamic Failure Process of Si3N4 Ceramics, Part II: Dynamic Fracture Toughness

摘要: A comprehensive experimental and theoretical work aiming at studying the dynamic failure process of silicon nitride ceramics has recently been started. The main goal is characterizing material behavior by mechanical microstructural features. basic force-, strengthand energy type characteristics completed with some fractographic analysis damage were discussed presented in a companion paper. current paper deals problem determining fracture toughness investigated ceramic, especially high loading rates. solution provided applying key curve (DKC) method, that utilizes observed important peculiarity nitride: it shows electric-emission activity during failure. This finding makes possible to determine time even cases impact tests rates, as well investigating notched specimens. qualitative quantitative fractography. Combining measuring results gained from instrumented findings, KId estimated based on features surface dynamically broken mirror size constant A0 also determined. INTRODUCTION wide choice testing methods relating determination quasi-static KIc engineering indicates efforts difficulties satisfy simultaneously demand reliable data economical technically simple procedures. Advanced, accurate, sensitive equipment are required for force small specimens tracing detecting extremely short processes loading. In case tests, special or JId values Fi,u, corresponding unstable crack propagation necessary calculations quasistatic relationships, cannot be taken load-time diagrams specimens, due undamped oscillations. was detail Part I related F-t shown. paper, will discussed. Alternatives above Three different methods, namely procedure response curve, dynamic-key-curve method reviewed compared aspect applicability given circumstances. An observation contributing find appropriate Si3N4 show electric emission which this an alternative way. Failure successfully macroand micro-fractographic investigations. Determining various fractography, nature peculiarities can analysed more complex Furthermore, properties like critical stress intensity factor compared. They may determined both analysis. EXPERIMENTAL WORK Investigated test series equipment, similar introduced CEAST 25/15/2 machine same instrumentation. Tested that, described preceding so ceramics, having composition 90% Si3N4, 4% Al2O3 6% Y2O3 investigated, produced Research Institute Technical Physics Materials Science Hungarian Academy Sciences (RITPMS, HAS). All uniaxial pressing using polyethylene-glycol additive. additive extracted heating air 600°C after pressing. firing pieces occurred two-stage gas-pressure sintering HIP equipment. rectangular prisms dimensions 4.9 mm x 3.2 49 mm. investigations executed two series, specimen positions geometry (see Figure 1.) according aim measurement. 1. Specimen arrangements tests. Direction L