Nicholas Andres Brake

Prediction of Transient and Steady-State Flexural Fatigue Crack Propagation in Concrete Using a Cyclic R-Curve

Fatigue damage in plain portland cement concrete is a nonlinear process that exhibits two distinct crack stages: a deceleration stage (transient crack growth) and an acceleration stage (steady-state crack growth). In the past, either the transient crack growth stage was completely neglected or was described using a power law that used crack extension as its argument. This works well for constant amplitude loading and for one geometry. However, to extend the fatigue prediction to variable amplitude loading, and also account for size effect, a fatigue crack resistance curve should be obtained so that the bridging stresses behind the crack tip can be calculated. In this paper, a new method has been developed to determine the fatigue crack resistance curve from crack rate and stress intensity data obtained from three point bending single edge notched specimens. The results of this study suggest that the fatigue crack resistance curve has a similar shape to the quasi-static crack resistance curve. Primarily, t...

Efficient Wireless Power Charging of Electric Vehicle by Modifying the Magnetic Characteristics of the Transmitting Medium

There is a developing enthusiasm for electric vehicle (EV) innovations because of their lower fuel utilization and greenhouse emission output. Integrating EVs with highway wireless power transfer (WPT) technology can appropriately reduce charging time and possibly expand their travel distance. There are several issues with the current WPT technology for EVs: 1) low efficiency due to large coil-coil distance and 2) slow charging time. Two ideas are proposed in this paper to increase system efficiency: 1) using a modified cement for covering the transmitting antenna area and 2) using high frequency wide bandgap switches, which can transfer a high amount of power in a short time. The optimization study of the receiving and transmitting coils is implemented with and without a core through 3-D finite-element analysis. The physics-based analysis is coupled with circuit-based analysis for utilizing high frequencies wide bandgap switch (SiC MOSFET). On the material side, the electromagnetic and mechanical properties of the modified cementitious composite are characterized and the results show significant improvement in the system efficiency.

Stability of Footings Adjacent to Pile Walls

AbstractThe stability of a footing may be destabilized near a retaining wall because of increased lateral displacement and decreased soil confining pressure. The stability of footing within this footing–soil–wall system is complex and not predicted using the classical solutions utilized for a semi-infinite footing–soil system. In this study, the bearing capacity of a concrete footing placed near a wall of spaced driven concrete piles using three-dimensional finite-element (FE) analysis with ANSYS 13.0 is investigated. All system materials are idealized as nonlinear, elastic–perfectly plastic, and rate independent using the upper bound function of the Drucker–Prager yield criterion. Three different soil deposits are studied: kaolin, silty clay, and kaolin–sand. A total of 144 unique FE analysis runs are executed. The footing bearing capacity is computed from the output footing pressure–settlement curve using several well-known postprocessing linearization criteria from which the lowest value is chosen. Soi...

Fatigue crack resistance characterisation of fully supported plain concrete beams

A framework for characterising the static and fatigue crack resistance of a fully supported beam on an elastic foundation is presented. The crack resistance is given as a function of the resisting cohesive stress and represented mathematically with a set of simple linear regression equations that can be easily integrated within a mechanistic–empirical design framework. The static crack resistance is derived using a weight function integral and reciprocal energy formulation that may be extended to more complex structural systems containing two-dimensional crack growth. Finally, a modified Paris law that utilises the crack resistance curves is used to develop a modified S–N diagram that can capture the fatigue response under various support conditions and different material characteristic lengths and structural sizes.

Efficient wireless power charging of electric vehicle by modifying the magnetic characteristics of the transmitting medium

There is a developing enthusiasm for electric vehicle (EV) innovations because of their lower fuel utilization and greenhouse emission output. Integrating EVs with highway wireless power transfer (WPT) technology can appropriately reduce charging time and possibly expand their travel distance. There are several issues with the current WPT technology for EVs: 1) low efficiency due to large coil–coil distance and 2) slow charging time. Two ideas are proposed in this paper to increase system efficiency: 1) using a modified cement for covering the transmitting antenna area and 2) using high frequency wide bandgap switches, which can transfer a high amount of power in a short time. The optimization study of the receiving and transmitting coils is implemented with and without a core through 3-D finite-element analysis. The physics-based analysis is coupled with circuit-based analysis for utilizing high frequencies wide bandgap switch (SiC MOSFET). On the material side, the electromagnetic and mechanical properties of the modified cementitious composite are characterized and the results show significant improvement in the system efficiency.

Characterizing Non-linear Fatigue Crack Growth and Size Effect in Plain Concrete Beams with a Hybrid Effective Crack and Cohesive Zone Model

The mechanical response of concrete is largely influenced by the interlocking coarse aggregate, which supplies the cement matrix with a resisting cohesive crack bridging force. Under low and high cycle fatigue loading, the cohesive stresses can influence the crack growth rate and the structural load capacity. A new method used to quantify the cyclic cohesive zone properties and effective crack resistance in three point bending single edge notch plain concrete specimens of different sizes under both low and high cycle fatigue loading is presented here. For validation, three point bend concrete specimens of two different sizes were tested under crack mouth opening displacement controlled low cycle quasi-static loading and force controlled high cycle fatigue using constant, variable, and random amplitude loading sequences. The results indicate that the cohesive stress-dependent cyclic crack resistance can be quantified and used to effectively characterize the high cycle fatigue non-linear crack growth and size effect.

Equivalent Crack, Fracture Size Effect, and Cohesive Stress Zone of Plain Concrete under Quasi-Static and Variable High-Cycle Fatigue Loading

AbstractCompliance-derived equivalent cracks are often used in high-cycle fatigue cracking predictions for computational expediency. Its dependence on the cohesive stress zone, however, may limit general applicability under high-cycle variable amplitude fatigue loading and limit the objectivity of the Paris constants and fatigue fracture toughness. In this paper, notched three-point bend concrete specimens of different sizes are subjected to (1)xa0different loading modes: quasi-static and high-cycle fatigue; and (2)xa0different fatigue loading sequences: constant, variable, and random. The results indicate that the fracture toughness does not depend significantly on loading sequence or loading mode. The Paris constants are not size dependent when a crack resistance curve is inserted into a modified Paris law within the range of experimental conditions considered here. The observations and statistical comparisons were consistent for both beam sizes, although they exhibited some significantly different cohesive...

Residual Strength of Pervious Concrete under Static and Impact Loading

Pervious concrete is a specialty mix consisting of coarse aggregate and cementing agents used primarily to improve drainage in parking lot applications, roadway shoulders, and low volume roadways. The porosity of the concrete is typically in the range of 10%-35%, which allows for rapid absorption of surface runoff. Although beneficial for this purpose, it is susceptible to raveling and typically has lower peak strength than conventional concrete. However, the residual strength, i.e. total fracture energy, characteristic length, brittleness ratio, and size effect are relatively unknown and have yet to be investigated thoroughly. This information can prove beneficial because it provides insight into the materials resistance to fatigue fracture, and its ductility and energy absorptiveness under impact. In this study, a series of geometrically similar three point bending single edge notch beams of three different sizes were tested under quasi-static loading. In addition, dynamic drop impact tests were carried out on pervious concrete disks to assess energy absorptiveness. The mode I residual behavior was observed to be ductile due to significant crack bridging and tortuosity. In addition, the characteristic length was quite large which precipitated strength domain response and not LEFM (Linear Elastic Fracture Mechanics). The total fracture energy for the largest size beam was approximately 110 N/m and the absorbed energy under impact was approximately 1.4 Joules. In addition, the excellent residual energy absorptive properties of the pervious concrete as shown in this paper, may lead to expanded use of this material for energy absorptive applications like highway median wall barriers upon further enhancement and optimization of the material constituency.

Plain Concrete Cyclic Crack Resistance Curves under Constant and Variable Amplitude Loading

Concrete pavement structures are subjected to a complex combination of environmental and traffic loads which produce a unique distribution of stresses at the critical mid-slab edge. Moreover, the fracture propagation caused by this unique distribution of stresses is a complex process because it is both size and load history dependent. In this study, a series of quasi-static, constant and variable amplitude fatigue tests on simply supported single edge notched beam specimens were conducted. It is shown that variable amplitude testing can providea comprehensive assessment of fatigue life because the R-ratio, peak stress intensity, and load history effects can be assessed. The results of this study also suggest that the fatigue resistance curve under variable amplitude has a similar quality to that under constant amplitude loading; there is a positive decreasing slope that asymptotes to a zero slope condition beyond the critical crack extension. However, the results show the magnitude of the critical crack extension and the maximum fracture resistances are not the same under the two different loading conditions.