Effects of moisture content and level in the crop on the engineering properties of alfalfa stems

Published Date

October 2008, Vol.101(2):199–208, doi:10.1016/j.biosystemseng.2008.07.006

PM—Power and Machinery

Title 

Effects of moisture content and level in the crop on the engineering properties of alfalfa stems

• Author 

• M. Nazari Galedar ^a,,
• A. Jafari ^a
• S.S. Mohtasebi ^a
• A. Tabatabaeefar ^a
• A. Sharifi ^b
• M.J. O'Dogherty ^c
• S. Rafiee ^a
• G. Richard ^d

• aDepartment of Agricultural Machinery Engineering, Faculty of Biosystems Engineering, University of Tehran, P.O. Box 4111, Karaj 31587-77871, Iran
• bAgricultural Engineering Research Institute, Karaj, Iran
• cCranfield University at Silsoe, Silsoe, Beds MK45 4DT, UK
• dNational Institute for Agricultural Research (INRA), Laon Cedex, France

Received 8 January 2008. Revised 17 June 2008. Accepted 14 July 2008. Available online 20 September 2008.

Some physical and mechanical properties of alfalfa stems are presented. The experiments were conducted at four moisture content levels from 10% w.b. to 80% w.b. and at three levels up the stem. At all levels along the stem, moisture contents less than 40% w.b. did not significantly influence major and minor diameters, thickness, cross-sectional area, second moment and polar moment of area. At the different moisture contents studied, the values of the tensile strength were within the ranges 9.24–26.35 MPa, 16.31–32.74 MPa, and 28.88–43.82 MPa for the upper, middle and lower levels in the crop, respectively. The maximum shear strength and shearing energy were 28.16 MPa and 345.80 mJ, respectively. The value of the bending stress obtained at the lowest moisture content was approximately 3 times greater than at the highest moisture content. The average Young's modulus ranged from 0.79 GPa to 3.99 GPa. The maximum and minimum of torsional stresses were found to be 4725 kPa and 465 kPa, respectively. The fact that a greater shearing energy was obtained at the lower levels in the crop could be due to the accumulation of more mature fibres in the stem. It was concluded that an increase in moisture content of stem leads to a decrease in the tensile strength, bending stress, Young's modulus, torsional stress, modulus of rigidity and to an increase in shear strength and shearing energy.

Nomenclature

A

cross-section area of wall (mm²)

a

semi-major diameter (mm)

b

semi-minor diameter (mm)

d₁

major diameter (mm)

d₂

minor diameter (mm)

E

Young's modulus (GPa)

En

shearing energy (mJ)

F_b

bending force (N)

F_s

shear force (N)

F_t

tension force (N)

G

rigidity modulus (MPa)

I_b

second moment of area (mm⁴)

I_p

polar moment of area (mm⁴)

l

length of specimen (mm)

ML

mass per unit length (g m⁻¹)

t

wall thickness (mm)

T_t

applied torque in torsional stress (N m)

ϕ

rotated angle stem in torsional stress (rad)

σ_b

bending stress (MPa)

σ_t

tensile strength (MPa)

τ_s

shear strength (MPa)

τ_t

torsional stress (kPa)

Fig. 1.

Fig. 2.

Fig. 3.

Fig. 4.

 Table 1

Table 1.

 Table 2

Table 2.

Fig. 5.

 Table 3

Table 3.

Fig. 6.

Fig. 7.

Fig. 8.

Fig. 9.

Fig. 10.

Fig. 11.

• ∗ 
  Corresponding author.

For further details log on website :
http://www.sciencedirect.com/science/article/pii/S153751100800216X