Applications of ceramic materials usually involve thermal stresses that can reduce their lifetime considerably. One of the most relevant mechanical properties for evaluating thermal shock damage resistance is the energy of fracture. In order to obtain this property, a stable crack growth regimen must be achieved throughout the test. In this paper, three-point bending tests are analyzed to determine how machine stiffness influences load point displacement rates. Understanding the differences between recorded and adjusted displacement rates is important in determining the stability of crack growth. This statement is corroborated by experimental data on sintered high-alumina, low-cement refractory castables. Keywords: energy of fracture, stable crack growth, 3-point bending test, refractory castable, stiffness. Resumo Em geral, a aplicacao de materiais cerâmicos envolve a ocorrencia de tensoes termicas que podem encurtar consideravelmente o seu tempo de operacao. Uma das propriedades mecânicas mais relevantes para a avaliacao da resistencia ao dano por choque termico e a energia de fratura. Para se obter isso, e necessario que ao longo do teste se atinja uma condicao de crescimento estavel de trinca. Neste artigo, analisa-se o teste de flexao em tres pontos para se determinar como a rigidez da maquina de ensaio influencia a taxa de deslocamento do ponto de aplicacao de carga. Para o estabelecimento da estabilidade do crescimento de uma trinca, e importante a compreensao das diferencas entre as taxas de deslocamento registradas e as ajustadas. Esta afirmacao e corroborada por dados experimentais obtidos com concretos refratarios de alta alumina e baixo cimento. Palavras-chave: energia de fratura, crescimento estavel de trinca, teste de flexao em 3 pontos, concretos refratarios, rigidez.
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