• Challenges in compression testing of 3D angle-interlocked woven-glass fabric-reinforced polymeric composites.

      Shah, S. Z. H.; Choudhry, Rizwan Saeed; Khan, Laraib Alam; University of Manchester; National University of Sciences and Technology; Centre of Excellence in Applied Sciences and Technology; National Univ. of Science and Technology, Islamabad, Dept. of Mechanical Engineering, College of EME Campus NUST 46000, PK, e-mail: Zulfihs84@gmail.com; HITEC Univ., Dept. of Mechanical Engineering, Taxila 47080, PK; and National Composites Certification and Evaluation Facility, Univ. of Manchester, Manchester, United Kingdom GB(Corresponding author), e-mail: rizwan.choudhry@gmail.com; Centre of Excellence in Applied Sciences and Technology (CESAT), 44000 Islamabad, PK, e-mail: laraibkh@gmail.com (ASTM International, 2017-09)
      This paper describes the challenges in using testing standards such as D6641/D6641M-14, for determination of compressive strength of 3D angle interlocked glass fabric reinforced polymeric composites (3D-FRPC). It makes use of both experimental investigation and finite element analysis. The experimental investigation involved testing both 2D and 3D-FRPC using ASTM D6641/D6641M-14 and subsequent scanning electron microscopic imaging of failed specimens to reveal the stress state at failure. This was further evaluated using laminate level finite element (FE) analysis. The FE analysis required input of effective orthotropic elastic material properties of 3D-FRPC, which were determined by customizing a recently developed micro-mechanical model. The paper sheds new light on compressive failure of 3D angle interlocked glass fabric composites, as only scarce data is available in literature about this class of materials. It showed that although the tests produce acceptable strength values the internal failure mechanisms change significantly and the standard deviation (SD) and coefficient of variance (COV) of 3D-FRPC comes out to be much higher than that of 2D-FRPC. Moreover, while reporting and using the test data some additional information about the 3D-fabric architecture, such as the direction of angle interlocking fabric needs to be specified. This was because, for 3D angle interlocking of fabric along warp direction, the strength values obtained in the warp and weft direction were significantly different from each other. The study also highlights that due to complex weave architecture it is not possible to achieve comparable volume fractions with 2D and 3D fabric reinforced composites using similar manufacturing parameters for the vacuum assisted resin infusion process. Thus, the normalized compressive strength values (normalized with respect to volume fraction) are the highest for 3D-FRPC when measured along the warp direction, they are at an intermediate level for 2D-FRPC and the lowest for 3D-FRPC, when measured in the weft direction.