On Damage Indicators in Strain-Controlled Cyclic Fatigue Tests of Porous Insulating Refractories

This paper discusses the degradation of two types of highly porous insulating firebricks under monotonic and cyclic loadings in uniaxial compression. Strain-controlled cyclic fatigue tests were performed with either constant strain limit or constant strain amplitude. Damage indicators are based on stress-strain data and impulse excitation technique. When the strain limit/amplitude was below the maximal strain of linear proportion of the materials, no damage was induced. This criterion was used to compare damage formation in the materials. In cyclic tests with constant strain limit, damage stagnated in the second phase of fatigue and no failure occurred. In cyclic tests with constant strain amplitude, the greater the strain amplitude, the lower the number of cycles the samples resisted before the failure. Damping was found a more sensitive damage indicator with higher variations than E modulus. Prediction of the damage state in the materials was possible with irreversible strain and dissipated energy data.