Poly(butylene terephthalate) (PBT) nanocomposites reinforced with different weight fractions of montmorillonite (MMT), and nanoprecipitated calcium carbonate (NPCC) were prepared by a two‐step melt compounding method. X‐ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses were employed to explore the effect of nanofiller inclusion on the crystalline structure of PBT nanocomposites. The mobile amorphous fraction (MAF) and the rigid amorphous fraction (RAF) were first measured using the specific heat capacity (Cp) and melting enthalpy data. However, the contributors to total RAF, including interfacial RAF (RAFint) and crystalline RAF (RAFc), could not be discerned using only DSC. A novel and simple method was hence developed by employing a combined DSC‐dynamic mechanical thermal analysis (DMTA) approach (CDDA) to disentangle the RAF components and determine the fractions of constrained volume constituents. To validate the results, the MAF calculated by CDDA were compared to those of DSC. The values obtained using CDDA were relatively higher, owing to the more significant sensitivity of this approach to polymer chain mobility.

A numerical study was performed to investigate the tensile properties of unidirectional fiber-reinforced composites containing co-polypropylene and short glass fiber (SGF) using a three-dimensional representative volume element (RVE) and finite element method (FEM). The initiation and propagation of interfacial crack were simulated based on a bilinear cohesive zone method (CZM). The FE simulation indicated that the transverse tensile strength of composite reinforced by SGF was strongly affected by the interface strength, critical fracture energy owing to interfacial debonding as well as loading direction. By increasing of SGF aspect ratio, the anisotropy of tensile strength was slightly affected; however, the anisotropy of modulus was noticeably elevated. The results of FE analysis indicated the proposed CZM can be used to simulate the crack-induced softening mechanism of reinforced thermoplastic polymers.

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