Title: Mechanical shear and tensile properties of selected biomass stems Authors
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 13, 2013
Publication Date: N/A
Interpretive Summary: Mechanical properties of biomass, such as tensile and shear stress energies, affect many biomass conversion processes. Baseline data on these properties are required in processing and handling equipment design and operation. In this research we used a specially designed universal testing machine to determine the mechanical properties of four major biomass crops of the Great Plains (big bluestem, corn stalk, intermediate wheat grass, and switchgrass). Our results showed that significantly greater energy was required to breakdown corn stalks during mechanical processing than was required for bluestem, switchgrass, and wheatgrass. We also observed that mechanical devices that use shear forces (e.g., knife mills or chippers) to reduce the size of biomass feedstock tended to be more energy efficient than other types of size-reduction machines. This new information will be useful to biomass conversion facilities in the design of processing and size-reduction technologies.
Technical Abstract: Lignocellulosic biomass, such as big bluestem, corn stalk, intermediate wheat grass and switchgrass stem are abundant and dominant species in the Midwest region of US. There is a need to understand the mechanical properties for these crops for better handling and processing of the biomass feedstocks. The objectives of our research included determination of tensile and shear stress of the selected biomass stems and evaluation of specific tensile and shear energies during failure. A high capacity MTI-100K universal testing machine equipped with adapted tensile clamps and a specially fabricated double-shear device was used for shear and tensile testing, respectively. Ultimate shear stresses were statistically the same for big bluestem, corn stalk and intermediate wheat grass with the values are 7.33, 8.53 and 6.23 MPa respectively, which was statistically less than switchgrass with the value of 13.39 Mpa. Corn stalks had the greatest ultimate tensile stress of 69.30 MPa, followed by switchgrass, big bluestem and intermediate wheat grass. The ultimate tensile stress and shear stress were statistically different for corn stalk and switchgrass. Both ultimate shear energy and specific shear energy for corn stalks was statistically different from the all other biomass crops. The shear to tensile stress ratios were 29.3%, 12.3%, 30.5%, and 31.9%, whereas the shear to tensile energy ratios were greater (42.2%, 67.2%, 61.2%, 50.4%) for big bluestem, corn stalk, intermediate wheat grass and switchgrass, respectively. Based on our results, shear-dominant size reduction devices (e.g. knife mills, chippers) tend to be more energy efficient and this feature should be taken advantage of when designing size reduction devices.