• 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.
    • Modelling of the buckling of a diaphragm–spine structure for a wave energy converter

      Collins, Keri M.; Meng, Maozhou; Le, Huirong; Greaves, Deborah M.; Bellamy, Neil; Plymouth University; University of Derby; Sea Energy Associates Ltd. (Elsevier, 2017-01-15)
      A wide range of wave energy converter (WEC) designs exists, and the SeaWave WEC uses an unstable buckled spine mode of operation. The SeaWave consists of a hose and buckled spine-diaphragm, which pumps air along the device under wave action. A physical model and finite element analysis (FEA) is compared to a previous theoretical model in this paper. The FE model was developed in ABAQUS 6.14 using shell, solid and contact elements and the analysis was done with a quasi-static approach to reduce the computational costs. The physical model was a scale version of the novel arrangement of the spine and diaphragm made from steel, polycarbonate and latex rubber. Geometry of the deformed device was investigated results showed an increase in transverse and longitudinal curvature as the compression rate increased. The FEA tended to overestimate the bending stiffness of the model, and hence the transverse curvature, because certain behaviours of the physical model were not captured. The force required to switch from one buckled state to another was measured both in the physical and FEA models and the potential energy storage was estimated to be 0.5 J/m of device at a compression rate of 0.1%.