Events Calendar

Scaling of Fracture in Quasibrittle Structures

Speaker: Qiang Yu, Northwestern University

Talk Title: Scaling of Fracture in Quasibrittle Structures

Abstract: Quasibrittle Materials, which include concrete, fiber composites, tough ceramics, bone and many other engineering materials, are widely used in the fields of civil engineering, aerospace engineering, mechanical engineering and bio-engineering. A salient feature of quasibrittle material is that its constituents are brittle and, due to heterogeneity, its fracture process zone is not negligible compared with the structure size. The consequence is that the structure strength (nominal stress at failure) is size dependent. Statistical studies showed that if size effect is ignored in concrete design, the failure probability may increase by orders of magnitude, e.g., from 10-6 to 10-3. Therefore, the proper scaling of quasibrittle structure strength is of great importance for structural safety and reliability.
In this study, the scaling of fracture in shear of RC beams, at reentrant corners, and in metal-composite hybrid joints is investigated theoretically, experimentally, and numerically. Dimensional analysis and asymptotic matching are exploited to identify the small- and large-size behaviors and the transition between these asymptotic trends. In contrast to notches and pre-existing cracks, the real part of the stress singularity exponent for the tip of a reentrant corner or bi-material corner is not -1/2, as required for finiteness of the energy flux into the crack. Therefore, one must take into account the fact that a cohesive crack must emanate from the corner and, for a large enough structure, must be embedded in a more remote singular stress field of the corner. The crack tip field, corner tip field and boundary influenced field are matched energetically through the strength of the singularities. By connecting the energy release and cohesive cracking of the embedded crack with the singular stress field of the corner, a general size effect law can be derived via asymptotic matching. The derived size effect laws for shear of reinforced concrete beams, for reentrant corners and for hybrid joints are validated by experiments and numerical simulations.


Host: Sonny Astani Dept. of Civil and Environmental Engineering

Location: Kaprielian Hall (KAP) - 209

Audiences: Everyone Is Invited

Contact: Erin Sigman