31 Mar 2025

Effects of Thermal Modification on the Flexure Properties, Fracture Energy, and Hardness of Western Hemlock

Abstract: This study investigates the effect of thermal modification on the flexural properties, transverse fracture energy, and hardness of western hemlock. Flexure tests on specimens featuring longitudinal and transverse grains showed that thermal modification at 167 °C leads to less statistical variability compared to unmodified samples. Additionally, thermal modification leads to a decrease in the transverse flexural strength. On the other hand, the fracture and Janka hardness tests revealed a more pronounced brittleness of the thermally modified samples. The total mode I fracture energy of modified single-edge notch bending samples was about 47% lower for radial–longitudinal systems and 60% lower for tangential–longitudinal systems. Similarly, the average Janka hardness in the tangential and transverse planes was 8.5% and 9.4% lower in the modified specimens, respectively. The results presented in this work show that thermal modification can have a significant effect on the fracturing behavior of west-ern hemlock and its energy dissipation capabilities. For design, this must be taken into serious consideration as these properties significantly influence the damage tolerance of this wood in the presence of stress concentrations such as those induced in bolted joints and cut outs. Fracture energy and hardness are also strongly correlated to ballistic performance.

11 Jul 2024

Sliver Spall Mitigation: Field Investigation, Laboratory Study, and Mixture Proportioning Analysis

Abstract: A combined field and laboratory study was conducted to identify factors contributing to sliver spall of concrete pavements and recommend avenues for prevention. In this study, spall density maps of eight airfields were created, and cores were taken for petrographic analysis. A companion laboratory study evaluated nondestructive testing equipment for identifying concrete prone to sliver spalling. Concrete mix designs with good and poor performance were analyzed for trends in mixture proportioning and aggregate gradation. Spall density mapping indicated sliver spalling was more likely to occur on longitudinal joints and that the distress was not solely a material or mixture design-related issue. The laboratory study concluded that surface resistivity measurements were able to differentiate edge-finishing techniques (normal versus overworked, mortar-rich edge) after seven days of curing. An analysis of particle packing theory and mixture proportioning trends showed there was substantial overlap in the gradations for good and poor performing pavement. Thus, acceptable mixture designs can produce poor quality pavement if not constructed properly. The main contributors to early age sliver spalling of concrete airfield pavement occur during pavement construction.

3 Feb 2022

Observation of Crack Arrest in Ice by High Aspect Ratio Particles during Uniaxial Compression

Abstract: In nature, ice frequently contains dissolved solutes or entrapped particles, which modify the microstructure and mechanical properties of ice. Seeking to understand the effect of particle shape and geometry on the mechanical properties of ice, we performed experiments on ice containing 15 wt% silica spheres or rods. Unique to this work was the use of 3-D microstructural imaging in a -10ºC cold room during compressive loading of the sample. The silica particles were present in the ice microstructure as randomly dispersed aggregates within grains and at grain boundaries. While cracks originated in particle-free regions in both sphere- and rod-containing samples, the propagation of cracks was quite different in each type of sample. Cracks propagated uninhibited through aggregates of spherical particles but were observed to arrest at and propagate around aggregates of rods. These results imply that spherical particles do not inhibit grain boundary sliding or increase viscous drag. On the other hand, silica rods were found to span grains, thereby pinning together the microstructure of ice during loading. These results provide insights into mechanisms that can be leveraged to strengthen ice.