Research Papers

Dynamic Fracture of Layered Plates Subjected to In-Plane Bending

[+] Author and Article Information
Servesh Kumar Agnihotri

Department of Mechanical Engineering,
Indian Institute of Technology Kanpur,
Kanpur 208016, India

Venkitanarayanan Parameswaran

Department of Mechanical Engineering,
Indian Institute of Technology Kanpur,
Kanpur 208016, India
e-mail: venkit@iitk.ac.in

1Corresponding author.

Contributed by the Materials Division of ASME for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received January 15, 2016; final manuscript received June 6, 2016; published online July 29, 2016. Assoc. Editor: Hareesh Tippur.

J. Eng. Mater. Technol 138(4), 041016 (Jul 29, 2016) (8 pages) Paper No: MATS-16-1016; doi: 10.1115/1.4033911 History: Received January 15, 2016; Revised June 06, 2016

Layered structures typically used in applications such as windshields, thermal protection systems, heavy armor, etc., have property jumps at the layer interfaces. Present study focuses on understanding crack initiation and propagation in such systems under dynamic loading particularly when the property jumps are across the crack front. Layered plates were fabricated by joining polymethylmethacrylate (PMMA) and epoxy sheets using an epoxy-based adhesive (Araldite). Single-edge notched (SEN) specimens were subjected to dynamic loading using a modified Hopkinson bar setup. High-speed imaging coupled with dynamic photoelasticity was used to record the crack-tip isochromatic fringes from which the stress intensity factor (SIF) history was obtained. In selected experiments, a pair of strain gages installed on surfaces of specimen was used to record the strain history in the layers, from which the SIF in each layer was obtained. The results indicated that, prior to crack extension, the strain in both layers was identical. The crack tips in the layers start extending at different time instants with the one in the relatively brittle epoxy layer extending first followed by the one in the PMMA layer. At low impact velocity, the delay obtained was significantly higher than that at high impact velocity. The speed of epoxy crack was lower initially due to the bridging of the crack by the uncracked portion of the PMMA layer till initiation of the crack in the PMMA layer. This effect reduced at higher impact velocity for which the delay was much lower and the cracks propagated at a higher-speed.

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Fig. 1

SEN specimen under three-point bending

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Fig. 2

Modified Hopkinson bar setup used for dynamic loading

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Fig. 3

Acute angle configuration

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Fig. 4

Isochromatics before crack initiation and during crack propagation in epoxy: (a) impact velocity = 1.75 m/s and (b) impact velocity = 5.61 m/s

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Fig. 5

Crack growth and DSIF history for epoxy impacted at two velocities: (a) 1.75 m/s and (b) 5.6 m/s

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Fig. 6

Strain histories in the epoxy and PMMA layers at two impact velocities

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Fig. 7

Crack-tip isochromatics in layered plates before crack initiation and during crack propagation: (a) E-P, impact velocity = 1.75 m/s,(b) E-P, impact velocity = 5.61 m/s, (c) P-E-P, impact velocity = 1.75 m/s, and (d) P-E-P, impact velocity = 5.61 m/s

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Fig. 8

Crack growth and DSIF history in layered plates at two impact velocities: ((a) and (c)) 1.75 m/s; ((b) and (d)) 5.6 m/s

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Fig. 9

Stages of crack growth in E-P plate impacted at 1.75 m/s: (a) t = 0 μs, (b) t = 10 μs, (c) t = 80 μs, and (d) t = 110 μs




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