18093
Both brittleness and loss of heterogeneity allow greater progression of microscopic cracks that can occur with usual physical activity ; in crack mechanical terms , normal mechanisms that dissipate crack tip growth energy are greatly reduced and crack progression is less impeded .
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Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 None