PSI - Issue 14

P Rama Subba Reddy et al. / Procedia Structural Integrity 14 (2019) 676–683 Author name / Structural Integrity Procedia 00 (2018) 000–000

679

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�1�

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2.5. Failure analysis Ultrasonic immersion C-scan analysis technique was used to assess the damage area of post impacted laminates. Automated C-scan system (M/s. Dhvani R&D Solutions Pvt Ltd, Chennai) with 1 MHz frequency probe having gain of 10, 15 and 20 db was used for scanning different thickness composite laminates. Damage area at different depth levels were assessed and compared for both the laminates. 3. Results & Discussion 3.1. Comparison of mechanical properties Table 1 shows mechanical properties of the laminates and it is observed that E-glass/epoxy laminate has higher mechanical properties than E-glass/phenolic laminate. The difference is more in flexural and ILSS than the tensile because these two properties are governed by the matrix and interfacial strength between the fiber and matrix. Fig.2 shows DMA results of the laminates. It is observed that phenolic laminate shows higher storage and loss modulus at all the frequencies compared to epoxy laminates. Storage modulus varied from 16500 MPa to 17500 MPa for epoxy laminate whereas phenolic laminate it shows 19500 MPa to 21500 MPa. Similarly loss modulus varied from 125 MPa to 750 MPa for epoxy laminate and for phenolic laminate it is 250 MPa to 1500 MPa. Higher loss modulus represents for lower interfacial strength between the fiber and matrix and also indicates more viscous behaviour of the laminate. Tan delta which is the ratio of storage modulus and loss modulus is plotted and obviously E glass/phenolic laminate has got higher tan delta values. Due to these properties it can be assumed that phenolic laminate may undergo more deformations through fiber stretching and delamination during the impact loads.

Table 1: Properties of composite laminate Property

E-glass/phenolic

E-glass/epoxy

Density, ( g/cc)

2.0 ± 0.02

2.0 ± 0.02

Resin content, (Wt %) Tensile strength, (MPa) Flexural strength, (MPa)

22 ± 1 370±10 350 ±10

22 ± 1 410±10 430±10

ILSS, ( MPa)

40± 3

50±3

Fig.2. DMA results of E-glass/epoxy and E-glass/phenolic laminates (a) Storage modulus (b) Loss modulus (c) Tan delta