SBIR: Hydraulically Controlled Tensile Testing of Concrete in Tri-axial Apparatus
Sponsor: US Army ERDC
Project Information
PI: Lauren Stewart
Student: Brett Reichard
Dates: June 1, 2014 - Dec 31, 2014
Funding: $100,000
Summary
Fracture mechanic theory for normal strength plain concrete has thoroughly been studied over the past decades. Through indirect and direct tensile testing techniques, the post-peak softening response of concrete has been established and utilized in finite element method (FEM) models to improve analysis simulations and to better understand concrete tensile behavior. However for more intricate concrete materials (e.g. fiber reinforced, high performance) under complex loading conditions, the required fracture properties are extremely limited and in need of further investigation.
Considering this lack of research, the objective of this thesis was to develop a uniaxial tensile testing technique to attain the post-peak softening response for ultra-high performance concrete (UHPC) under confining pressure. This particular multi-axial behavior is valuable in improving material models for US Army applications into hardened target structures.
To meet the goal of this thesis, a detailed literature review was initially performed. Understanding the development and background behind basic concrete fracture mechanic models as well as the previous approaches and techniques that have been used in performing uniaxial tensile tests, allowed this researcher to properly analyze the work completed earlier in the experimental program. A new testing methodology was then developed which enabled for the testing frame itself to apply a stiffening force, while an external hydraulic plunger cylinder (HPC) performed the uniaxial tensile test. Eight tests were performed on UHPC specimens with half maintaining stability throughout their entirety. The positive and negative aspects of these tests were analyzed and improvements were described which would provide increased testing stability and accuracy of measurements.
This unique testing scheme enables for tensile testing under confining pressures in the US Army Corps of Engineers’ Engineer Research and Development Center (ERDC) compression-only pressure vessel. In addition, the developed testing scheme can be implemented into typical testing frames to perform stability-critical uniaxial tensile tests on concrete specimens.
Publications
Reichard, B., Stewart, L.K., Weaver, M., Morrill, K. Coupled Hydraulic System for Tensile Experiments in Compression-only Machines. (2016). Experimental Mechanics,56(7), 1179-1190. Link to pdf
Reichard, B. (2015). Uniaxial tensile testing technique to obtain softening response of ultra-high performance concrete under confining pressures. Link to thesis.