PSI - Issue 5

A.A. Abd-Elhady et al. / Procedia Structural Integrity 5 (2017) 19–26 Mubaraki et al./ Structural Integrity Procedia 00 (2017) 000 – 000

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2. Numerical work

2.1. Mechanical properties of the materials and specimen geometries

The major advantages in using SCB are that it has a simple geometry, it has a simple loading configuration, and different modes of mixity can be obtained. Three types of SCB geometry are used in the present work, as shown in Fig. 1. The dimensions of the specimens used in the present work to get different modes of mixity are tabulated in Table 2. The modulus of elasticity, Poisson's ratio, tensile strength, and flexural strength measured by Hossiney et al. (2010) and Su (2013), as shown in Table 1, were used in the present work to study the effect of the RAP% and W/C ratio on the fracture behavior of concrete pavement.

Table 2. Specimen geometry to simulate mixed mode I/II crack growth

Radius, R (mm)

Crack Ratio, a/R

2S (mm)

S1 (mm)

S2 (mm)

Pure Mode I

Pure Mode II

Mixed Mode I/II

Specimen

L/R

o

b 0

SCB-1

50 50 50 50 50 50 50 50 50 50 50 50

0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2

80 80 80 60 60 60 60 60 60 50 50 50

40 40 40 30 30 30 40 40 40 40 40 40

40 40 40 30 30 30 20 20 20 10 10 10

0 0 0 0



25 50





SCB-2

0 0 0 0 0 0 0 0 0



0.272 0.544 - 0.128





SCB-3-1



0.14 0.34





SCB-3-2

- 0.224



0



0.1



2.2. Finite element analysis The fracture behavior of concrete pavement containing different RAP% and W/C ratio has been investigated by using Abaqus/Explicit and Abaqus/Standard finite element codes (2016). The concrete was assumed as isotropic and homogeneous material and in elastic state. The meshes were constructed with hexagonal structural mesh, C3D8 (8 node linear brick) elements; around 30000 elements are used in the present model. The size of element decreases gradually with decreasing the distance from the tip of the pre-crack. This means that FE meshes in the neighborhood of the pre-crack are much denser. X-FEM was used for simulating the crack propagation in various crack analysis problems such as in Abd-Elhady and Sallam (2015), Mahmoud et al. (2014), and Mubaraki et al. (2013). In the present investigation, crack growth direction was chosen as that normal for the direction of maximum tensile stress. 3.1 Crack path Figure 2 shows typical crack paths in SCB specimens for cracks emanating from pre-crack with different SCB geometries. As shown in Fig. 2.a, SCB-1 specimen, by changing the pre-crack inclined angle, b , the mode of mixity increases. When b = 0 o , mode I occurs and cracks initiate and propagate parallel to the load and perpendicular to the tensile stress, as shown in Fig. 2.a-1. Furthermore by increasing the value of b , the mode of mixity increases to reach the maximum of b = 50 o as pure mode II. By increasing b , the fracture path deviates from the original inclination angle and grows along a curvilinear trajectory to extend toward the upper loading point as shown in Fig. 2.a-2 and 2.a-3. Figure 2.b shows the effects of the value of distance L on the crack path at different modes of mixity for SCB 2 specimen, i.e., S1 = S2 = S. At L = 0, the crack initiates at pure mode I, while, when L increases the mode of mixity increases and reaches pure mode II at L/R = 0.544. Figures 2.c and 2.d show the crack path for SBC-3 when S1  S2. It is clear that pure mode I and pure mode II occurring at different values of L . It can be concluded that, when S1 = S2 the crack path at different modes of mixity can be changed by changing the value of b or L. 3. Results and discussion