PSI - Issue 50

Alexander Eremin et al. / Procedia Structural Integrity 50 (2023) 65–72 Alexander Eremin / Structural Integrity Procedia 00 (2019) 000 – 000

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wide spread of fiber reinforced polymers (FRP) in high-tech industries: aerospace, automotive, marine, etc. Besides the improved properties there are technological advantages of such materials. Highly productive methods like filament or tape winding and automatic layup allow molding the whole structures while reducing the amount of traditional fasteners (rivets, bolts, etc.). As a result more of novel aircrafts are designed with carbon fiber reinforced polymer (CFRP) wings, wingboxes, fuselages, etc. For efficient design and simulation of structures engineers demand the structural and functional properties to be reliably estimated. There are lots of testing techniques governed by different standards which propose test parameters, equipment, and data processing algorithms. Moreover, carbon fibers could be replaced in some cases by aramid ones to increase the impact resistance by improving fracture toughness. However novel scientific methods emerge and one of them is Digital image correlation (DIC) described by Sutton et al. (2009). It has spread significantly with an advance in digital cameras and it can be extended to almost any imaging technology. In the field of testing of structural materials DIC can provide a full-field evaluation of specimens allowing detection of material irregularities, measurement of strains and strain-dependent properties like elastic modulus or Poisson ratio, investigation of stress-concentration areas, etc. presented in Lecomte-Grosbras et al. (2009), Laurin et al. (2012), Vrgoč et al. (2021) and Ji et al. (2013). Basic set of parameters provided by DIC can replace traditionally applied extensometers and strain gauges. Extended full-field analysis can be a source of additional data for more reliable estimation of mechanical properties. The study of composites under various loading conditions is important. However, one of the important properties is in-plane shear strength, which is rarely investigated and presented in Ullah et al. (2011), Liang et al. (2013) and Martin-Barrera et al. (2018). The present paper deals with investigation of mechanical properties of aramid and carbon fiber reinforced polymer specimens with different layups. Digital image correlation was utilized to process the images of the specimen’s surfaces capture d throughout mechanical testing and to obtain the strain data. The strain fields are presented and analyzed in order to reveal the difference in deformation and fracture of different AFRP and CFRP layups. 2. Composite manufacturing procedure Composite specimens were manufactured from thermosetting prepregs. CFRP laminates were moulded using UTS150-DT190 prepreg with unidirectional carbon tapes (UTS150, density 150 g/m 2 ) and epoxy binder DT190. AFRPs were moulded using a 5H satin woven prepreg with AA285 aramid fabrics (density 172 g/m 2 ) and the same epoxy binder. Nominal thicknesses of the plies are 0.125 mm and 0.17 mm correspondingly. The blanks had a size of 215 х 150 mm. Prepregs were laid up using prescribed stacking sequence and then hot-pressed using Gotech 7014 at 120 С and 0.7 MPa during 1 hour. After a preliminary curing, vacuum and perforated films, peel and breather plies were removed and the laminate was postcured in a heated oven at 100 C and ambient pressure during 24 hours. After manufacturing the specimens were cut using CNC milling machine Purelogic RM0813. Polycrystalline diamond tools with a water flood were used for CFRPs while carbide mills with air cooling were utilized for AFRPs. After cutting the specimens were visually inspected for defects in order to fit the testing standards. 3. Mechanical testing techniques 3.1. In-plane shear response by tensile testing of ±45° laminate ASTM D3518 «Standard Test Method for In -Plane Shear Response of Polymer Matrix Composite Materials by Tensile Test of a ±45° Laminate» proposes a test to determine in-plane shear properties by tensile testing of a laminate having reinforcing fibers oriented at an angle of ±45° to the loading axis. Testing equipment was the same as used above. Loading rate was 1.8 mm/min. The specimens had width and length of 215 х 25 mm 2 ; thickness of CFRPs with a layup [45/-45] 5S was 2.5 mm, while AFRP was 2.1 mm thick ([45 F ] 6S ). For each material five specimens were tested.