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Mechanical Properties of Brittle Ceramics: Case Study of Boron Rich Ceramics and Acropora cervicornis Coral Skeleton
Title
Mechanical Properties of Brittle Ceramics: Case Study of Boron Rich Ceramics and Acropora cervicornis Coral Skeleton.
Creator
Carrasco-Pena, Alejandro, Kwok, Kawai, Orlovskaya, Nina, Gou, Jihua, Uribe Romo, Fernando, University of Central Florida
Abstract / Description
Ceramics are ubiquitous in man-made and natural structures. Their mechanical properties highly depend on their composition, microstructure and level of defects in the bulk of the material, the latter affecting the integrity of the components; such is the case of boron-rich ceramics where large agglomerates create high stressed regions, or coral skeleton where porosity determines their strength against hydrodynamic forces present in the ocean tides. Therefore, studying the properties of...
Show moreCeramics are ubiquitous in man-made and natural structures. Their mechanical properties highly depend on their composition, microstructure and level of defects in the bulk of the material, the latter affecting the integrity of the components; such is the case of boron-rich ceramics where large agglomerates create high stressed regions, or coral skeleton where porosity determines their strength against hydrodynamic forces present in the ocean tides. Therefore, studying the properties of ceramic materials using invasive and non-invasive methods helps in the understanding of the link between the properties and the performance of the structures. The aim of this research was to test the novel ceramic component ZrB2-30wt%SiB6 and Acropora cervicornis coral skeleton using non-conventional techniques that allow for the study of their mechanical properties and their behavior when exposed to external loads present in their environments of application. The first part of this study focuses on understanding the effects of adding SiB6 to enhance the mechanical properties of ZrB2 ceramics for their ultra-high temperature use. The second part will emphasize in the behavior of Acropora cervicornis coral skeleton when exposed to compressive forces and the effects porosity has on this structure when subjected to such loads. It was found that the SiB6 phase was not stable after sintering of the composite and large agglomerates were present in the surface of the material acting as stress concentrators, thus compromising the biaxial strength of the component that resulted to be 224.9 MPa. It was also found that coral skeletons are highly susceptible to porosity which creates variability on the elastic modulus ranging from 60-1 GPa for simulated porosity of 0-90% respectively and a strength of 3.56 (&)#177; 0.31 GPa obtained through Vickers indentation. Finite element models were developed and validated against experimental results for the ZrB2-30wt%SiB6 and Acropora cervicornis coral skeleton.
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Date Issued
2019
Identifier
CFE0007440, ucf:52696
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0007440
POLYURETHANE FIBER REINFORCED POLYMER STRENGTHENING OF SHEAR DEFICIENT REINFORCED CONCRETE BEAMS
Title
POLYURETHANE FIBER REINFORCED POLYMER STRENGTHENING OF SHEAR DEFICIENT REINFORCED CONCRETE BEAMS.
Creator
Al-Lebban, Yasir, Mackie, Kevin, Chopra, Manoj, Makris, Nicos, Gou, Jihua, University of Central Florida
Abstract / Description
The use of externally-bonded fiber-reinforced polymer (FRP) composites has been established as an effective means for the strengthening of shear-deficient reinforced concrete (RC) flexural members. Epoxy-based wet layup systems were predominantly employed in previous studies. In this study, carbon FRP pre-impregnated with polyurethane resin is utilized in strengthening shear-deficient RC beams and compared to an epoxy resin. Fourteen small-scale (96 in span, 6 in width, and 12 in height) and...
Show moreThe use of externally-bonded fiber-reinforced polymer (FRP) composites has been established as an effective means for the strengthening of shear-deficient reinforced concrete (RC) flexural members. Epoxy-based wet layup systems were predominantly employed in previous studies. In this study, carbon FRP pre-impregnated with polyurethane resin is utilized in strengthening shear-deficient RC beams and compared to an epoxy resin. Fourteen small-scale (96 in span, 6 in width, and 12 in height) and five large-scale (132 in span, 12 in width, and 17 in height) flexural specimens were tested, considering FRP system type (polyurethane versus epoxy), size effect, shear span-to-depth ratio, FRP configuration (U-wraps versus side bonding), and FRP scheme (sheets versus strips with 45o or 90o). Experimental strength testing under four-point loading demonstrated similar or enhanced shear capacity when strengthening by the polyurethane compared to the epoxy composite systems.The shear behavior of polyurethane-based FRP composite system is investigated in this research using analytical and numerical approaches. A closed-form mechanics-based analytical model, utilizing the principle of effective FRP stress and upper-bound theorem, illustrated that the shear behavior and debonding mechanism were dependent on both FRP composite and bond characteristics. The analytical model is expressed in terms of shear crack opening crossed by the FRP laminate and gives good agreement with experimental results. The finite element analysis (FEA) model shows that the stresses in the FRP are not in single direction as in the coupon tests, and the biaxial stress states should be taken into consideration.The structural behavior of RC members strengthened with externally-bonded FRP composites is mobilized through the composite action technique. Bond stress can be defined as the shear stress acting in the interface between FRP and concrete. It is of crucial importance to evaluate the failure mode behavior. Debonding (loss of adhesion) failure is one of the most common modes of failure encountered in shear strengthening RC members in practice. Numerous constitutive bond-slip models have been proposed and derived numerically and mathematically based on experimental data with an assumption that the FRP width bp is taken as a variable and all stresses or strains at the same longitudinal coordinate (L direction) are uniform. No attention has been given to study the bond states of stress which are mainly altered by the inclined shear cracks in concrete. A new bond-slip law was proposed to address the biaxial two-dimensional (2D) states of stress problem. Numerical solution by finite difference (FD) was conducted to solve four partial differential equations per node (2 for FRP and 2 for concrete in each direction) with appropriate boundary conditions to obtain the stresses, slips, and strains based on the proposed bond-slip model. A new experimental setup was proposed to represent the 2D bond-slip model by lap shear tests in both directions by laminating two perpendicular strips on concrete blocks with the proposed strain profile. Experimental calibration has been carried out by using nonlinear least-squares regression (fitting) of the experimental strain data with the numerical FD equations to obtain the bond-slip parameters for the 2D FRP-to-concrete polyurethane interface system.
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Date Issued
2017
Identifier
CFE0006852, ucf:51737
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFE0006852
EQUIBIAXIAL FLEXURAL STRENGTH TESTING OF ADVANCE CERAMICS
Title
EQUIBIAXIAL FLEXURAL STRENGTH TESTING OF ADVANCE CERAMICS.
Creator
Jordan, Ryan T, Orlovskaya, Nina, Kwok, Kawai; Ghosh, Ranajay, University of Central Florida
Abstract / Description
Ceramics are very important materials with many unique properties used in numerous industrial applications. Ceramics could be very hard and very strong in comparison to metals; however, they are very brittle, thus they are prone to instantaneous and catastrophic failure. Therefore, their reliability is compromised and it is very important to have advanced techniques that allow evaluating their mechanical behavior in many unusual stress states. One of such testing methods is biaxial strength...
Show moreCeramics are very important materials with many unique properties used in numerous industrial applications. Ceramics could be very hard and very strong in comparison to metals; however, they are very brittle, thus they are prone to instantaneous and catastrophic failure. Therefore, their reliability is compromised and it is very important to have advanced techniques that allow evaluating their mechanical behavior in many unusual stress states. One of such testing methods is biaxial strength method, that allows to measure properties not only unidirectional, but also in a biaxial way. The research work for this thesis will be built on design and development of ring-on-ring test jigs that will measure a biaxial strength of thin ceramic disks.
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Date Issued
2018
Identifier
CFH2000386, ucf:45700
Format
Document (PDF)
PURL
http://purl.flvc.org/ucf/fd/CFH2000386