Investigation of the ductile deformation potential of microscale epoxy materials

Abstract

In fiber reinforced polymers (FRP), the matrix, e.g. an epoxy system, usually has a microscopic size and therefore may have other properties than the standard bulk samples. It is known that a size effect exists, for epoxy also in terms of ductility or plasticity. However, to date, there is no physical, mechanochemical or molecular explanation for the correlation of plasticity and gauge volume, especially for an archetypical brittle standard epoxy matrix. The specific limits of the gauge volume for these ductile effects are unknown as well. Therefore, a new manufacturing method to produce thin epoxy films with thicknesses between 15 and 100μm is developed. These films are investigated by differential scanning calorimetry (DSC) with regard to the degree of cross-linking. The mechanical properties are determined by tensile and creep test, also at different temperatures. In the next step, a suitable analysis method for the correlation of molecular structure and mechanical deformation behavior is developed. Manufactured films are investigated by ex situ and in situ infrared spectroscopy (IR) to analyze the molecular mechanisms caused by load introduction. Various pre-processing and interpretation methods for the determination of spectral changes, such as peak shifts, are used to figure out the specific molecular changes related to the mechanical stress from the raw spectral data. It was possible to detect molecular changes of the highly cross-linked macromolecules as a result of plastic deformation caused by tensile load. Shear bands and necking are visualized by photoelastic analysis and a better understanding of the brittle material’s ability to form shear bands is achieved.

Keywords

• Brittle-to-ductile transition
• Plasticity
• Thermomechanical behavior
• Size effect
• Infrared spectroscopy
• Peak shift