Nanoindentation of neat and in situ polymers in polymer–matrix composites

Nanoindentation experiments were performed on neat and in situ polymers in two different composite materials (IM7/977-3 and AS4/APC-2) and an adhesive (FM 300). The objective was to determine whether differences in modulus and hardness result from composite manufacturing procedures. Since the aim was to measure material properties, acceptable comparisons with neat properties could only be made using unconstrained, cured in situ tests. Measurements of modulus and hardness were made using two different techniques on two different indenters at a range of loads and penetration depths. The load–penetration depth data from the neat and in situ tests were compared to determine whether the fiber constraint affected the in situ tests and quantitative measures were implemented to determine whether an in situ test was unconstrained and therefore acceptable. The results of this comparison between neat and acceptable in situ tests showed a clear increase in modulus and hardness for the cured in situ materials, indicating that the materials are modified in some fashion by the manufacturing process. A finite element analysis of the in situ indentation experiment was performed to determine the required size for a polymer pocket that would minimize the constraint of the fibers on the polymer deformation response.