Effect of moisture and temperature on fracture behavior of graphite-epoxy laminates

Abstract

The hygrothermal effect on the fracture behavior of T300/934 graphite/epoxy laminates have been investigated. In order to study this, compact tension specimens were prepared for the laminates with (90) 16, ( 0 90 ) 4s, (±45) 4 s and (0/± 45 90 ) 2s lay-ups. The specimens were dried and some of the dried specimens were exposed to various hygrothermal conditions to obtain different moisture contents prior to testing. Both dry and wet specimens were tested at different temperatures to assess the fracture behavior including the fracture toughness. It is determined that the effect of temperature on dried laminates is to decrease fracture toughness around room temperature for (±45) 4 s and ( 0 90 ) 4s laminates and around −23°C for (90) 16 laminate as temperature is either increased or decreased. For the quasi-isotropic laminate, the behavior is different. Fracture toughness follows the trend of other laminates up to about 120°C. Beyond this point fracture toughness begins to increase. The effect of moisture is seen to either increase or decrease the fracture toughness depending on the laminate and environmental history. In addition, the effect of hygrothermal conditions on tensile strength of unnotched specimens has been studied and the test data are compared with the predictions using laminate theory and tensor polynomial failure criterion. Some anomalies using the laminate theory to predict the strength are also discussed.