A Computer-Based Justification for Using the Simple Bend Test as the Basis for Predicting the Performance of Steel Hooked-End Fibres in Reinforced Concrete

• Main Author: Bam, T J
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2019
• Subjects: Cement; Cold; Composite materials; Concrete; Deformation; Energy; Friction; Geometry; Impact strength; Industrial engineering; Inverse problems; Kinematics; Load; Manufacturing; Materials science; Mathematics; Mechanical properties; Mechanics; Reinforced concrete; Residual stress; Stress-strain curves; Tensile strength; Wire drawing; Yield stress
• ISBN: 9798380906654

The classical test to confirm the performance of a given fibre design for use in reinforced concrete is the pullout test. While attempts have been made to simulate the performance of such pull-out tests, in practice it has been found that there is a significant disparity between prediction and real-life performance.The high strength of steel reinforcing fibres is a consequence of the cold wire drawing process and subsequent fabrication. Residual stresses exist in cold drawn wire as a consequence of the elastic response to a non-uniform distribution of plastic strain. This also introduces a yield strength profile where yield strength varies radially through the wire. The question arises as to whether fibre design should use a starting material model that considers these properties.This thesis examines whether the tensile test, simple bend test and pull-out test provide enough information to define a starting material model that may be used for further design and simulation of such fibres.Since the details of the wire drawing process and material specification are proprietary and therefore unknown, a sensitivity study was conducted to determine which aspects of the wire drawing process have the greatest effect on the pull-out curve and the following were established as being significant: • Plastic strain due to wire drawing was shown to be the most important factor. • The bilinear curve was shown to be a suitable approximation for the stress-strain curve. • Replacing the plastic strain profile with a single value of average equivalent plastic strain is practical.The following were established as having negligible effect: • The consequences of the hooked-end forming process. • The residual stress profiles due to wire drawing provided that the above was also excluded. • The hardening lawWhile inverse analysis demonstrated that all tests provide sufficient information to determine the required properties for this bilinear material model, the pull-out test was shown to provide more accurate approximations of the maximum pull-out force at the first and second peaks and the bend test was shown to produce more accurate approximations of the energy associated with pull-out. Good correlation with the baseline pull-out curve was found for both the isotropic and the kinematic hardening laws and it is concluded that behaviour during pull-out is insensitive to the hardening law.Sensitivity analysis and characterisation of the material model using an experimental pull-out curve demonstrated the importance of the coefficient of friction. Full characterisation using the pull-out curve therefore requires the solution to a three-variable problem: yield strength, tangent modulus and coefficient of friction. This was a suggested topic for further study.