Wang, Weijin
(2017)
Subcritical Crack Growth Induced by Stress Corrosion in Quasibrittle Materials.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
For concrete structures, a primary driver of deterioration shortening their lifespans is the damage growth resulting from coupled chemo-mechanical attack. Under sustained service load coupled with corrosion, stress corrosion cracking will happen and lead to subcritical crack growth (SCG) in concrete members. Thus, knowledge of the SCG in cement-based materials subject to concurrent physical and chemical attacks is of great importance for understanding and mitigating the chemo-mechanical deterioration in concrete structural members.
In this thesis, the SCG in hardened cement pastes is investigated experimentally by a novel test approach aided with micro-characterization. Specimens of negative geometry are designed, which enable the use of load control to trigger stable crack propagation in hardened cement pastes. Specimens from the same batch of mixture (with water/cement ratio w/b = 0.35 and 0.40) are exposed to the same chemical condition and loaded at the same age for both the static fatigue and stress corrosion groups. The average trend and the associated variation of the dependence of crack velocity v on the stress intensity factor K at the crack tip are obtained by using a high-resolution microscopy system to trace the crack tip. Three distinctive regions are captured in the K-v curves of stress corrosion specimens, which is different from those in static fatigue. With the help of advanced techniques including SEM, AFM and Raman spectroscopy, the microstructure destruction and chemical composition change induced by the imposed chemo-mechanical attack are characterized at different stages. In addition to the physical insights for deeper understanding of the coupled effect of chemo-mechanical attack, these experimental results provide important macro- and microscopic benchmarks for numerical modeling.
Moreover, anchored at the obtained experimental benchmarks, material modeling and numerical schemes are developed to approximate the coupled chemo-mechanical deterioration in cement-based materials. To utilize the unique physical or chemical laws involved in each individual deterioration process, a two-dimensional (2D) discrete model consisting of two lattice systems is constructed in this study to approximate the meso-structure of cementitious materials. These two lattice systems, one approximating the dissolution of cement matrix under calcium leaching and the other simulating the response of material skeleton to external loads, are interlinked by a common physical variable – the porosity of hardened cement pastes, which evolves with the interaction of skeleton cracking and cement dissolution. To reduce the computational cost, an artificial time scale, which allows coarse temporal discretization, is used in the numerical framework resting on a hybrid of implicit and explicit formulation. The model is implemented in ABAQUS and validated by the experimental results. The numerical results show that the proposed discrete model can realistically describe the SCG in hardened cement pastes subject to coupled mechanical damage and calcium leaching.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
14 June 2017 |
| Date Type: |
Publication |
| Defense Date: |
29 November 2016 |
| Approval Date: |
14 June 2017 |
| Submission Date: |
16 February 2017 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
102 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Civil and Environmental Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Subcritical crack; Stress corrosion; Chemo-mechanical deterioration; Negative geometry; 2D Lattice model; Two-way coupling. |
| Date Deposited: |
14 Jun 2017 17:25 |
| Last Modified: |
14 Jun 2017 17:25 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/30876 |
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