| Popis: |
The objective of this study was a values evaluation of fracture toughness of fiber-metal laminates (FML) compounded from carbon fibers in epoxy matrix and aluminium plates of lay-up 6/5. Samples with unidirectional and bidirectional orientation were tested experimentally. In the case of unidirectionally oriented samples an effect of moisture absorption to epoxy matrix on the values of fracture toughness was reviewed. A fracture toughness calculation was realized by COD method firstly. A bigger pop-ins in F – COD diagram as critical moments for "delta"c evaluation were considered; it was determined by 5% tangential line. It was found out, that results of this measurement weren’t in agreement with plane deformation condition and for this the results couldn’t be rated as fracture toughness "delta"Ic. A method of J integral for fracture toughness evaluation was used consequently. A test of elastic compliance changes before J integral calculation by all of samples was performed. Beginning of stable grow of crack was determined by this method. A critical forces Fc from beginnings were established, which were used for calculation of Jc. A functional dependence of elastic compliance on crack opening had specific waved shape before its linear (up to exponential) grow. It was observed in all cases. The critical forces Fc from the end of “wave” preceding the continual grow of compliance were determined. Equations stated in standards for J integral calculation were used, which are for metal materials normally used. Despite this was found out all of results of Jc were in good agreement with plane deformation condition and could be rated as fracture toughness JIc. In this study were found out these pieces of knowledge about fracture toughness of FML CARE: Unidirectional CARE had fracture toughness JIc about 76 kJ/m^2 and the same type but with bigger amount of absorbed moisture had JIc about 4 % higher. In this case negative moisture influences on CARE weren’t found. Bidirectional CARE had fracture toughness JIc about 31 kJ/m^2; it was about 65 % less then in the case of unidirectional CARE |
