Visualization method for stress-field evolution during rapid crack propagation using 3D printing and photoelastic testing techniques

Abstract

Quantitative visualization and characterization of stress-field evolution during fracture rapid growth is critical for understanding the mechanisms that govern the deformation and failure of solids in various engineering applications. However, the direct capture and accurate characterization of a rapidly-changing stress field during crack propagation remains a challenge. We report an experimental method to quantitatively visualize and characterize rapid evolution of the stress-field during crack propagation in a transparent disc model containing a penetrating fusiform crack. Three-dimensional (3D) printing technology and a stress-sensitive photopolymer resin were adopted to produce the disc model and to alleviate the residual processing stress that usually blurs the dynamic stress field due to overlap. A photoelastic testing system that synchronized a high-speed digital camera and a pulsed laser with a nanosecond full width at half maximum (FWHM) was used to capture the rapid evolution of the stress field in the vicinity of crack tips. The results show that the proposed method is suitable to directly visualize and quantitatively characterize the stress-field evolution during crack rapid propagation. It is proved that the crack propagation velocity is strongly governed by the stress field around the crack tips.

Figure 1

Fusiform crack disc. (a) Schematic of the disc; diameter D = 50 mm, thickness B = 7.76 mm and internal aperture length L = 15 mm; (b) photograph of printed photosensitive resin sample.

Figure 2

Disc (a) before and (b) after loading in a circularly-polarized field, when the crack appears (D = 50 mm, L = 15 mm).

Figure 3

High-speed photoelastic testing system. (a) Pulsed-laser light source, portable loading machine, polarizer, wave plate and high-speed camera; (b) display and control systems of the high-speed camera and portable loading machine

Figure 4

(a) The optical arrangement that produces the circularly-polarized field; (b) oscillogram and characters of the nanosecond FWHM pulsed-laser source.

Figure 5

Diagram of the pulsed laser source synchronized with the photo-frequency of the high-speed digital camera.

Figure 6

Stress components around the crack tip in the stress plane.

Figure 7

Half-integer isochromatic fringes at the near-tip region during crack propagation recorded in 10 µs intervals. (a) Field of view, 25.3 mm × 19.0 mm; (b) recorded in 0 µs; (c) recorded in 10 µ µs; (d) recorded in 20 µs; (e) recorded in 30 µs; (f) recorded in 40 µs; (g) recorded in 50 µs; (h) recorded in 60 µs; (i) recorded in 70 µs; (j) recorded in 80 µs.

Figure 8

Deviator stresses at half-integer isochromatic fringes, given in MPa. (a) 0 µs; (b) 10 µs; (c) 20 µs; (d) 30 µs; (e) 40 µs; (f) 50 µs; (g) 60 µs; (h) 70 µs; (i) 80 µs.

Figure 9

Maximum deviator stress at the crack tip and crack tip velocity as a function of crack length during crack propagation. (a) sample 1; (b) sample 2.

Figure 10

SIF during crack propagation as a function of crack length.