BAE2022/BAE4400 Physical Properties of Biological Materials Lecture 11 Test next Monday: covers material through today and Wednesday Review on Wednesday Class lecture on Friday starts material for Test 2 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

BAE2022/BAE4400 Physical Properties of Biological Materials Lecture 11 - Rheology 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Lecture 11 – Friction and Flow Chapter 9 Page 239 – 256 Friction of Solids and Flow of Granular Solids 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Lecture 11 – Friction and Flow original Coulomb’s law: proportional to normal force (load) independent of area of sliding surfaces Independent of velocity Depends on materials in contact 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Lecture 11 – Friction and Flow Tribology: the study of friction and interaction between solids with relative motion between 2 surfaces in contact with each other. 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Lecture 11 – Friction and Flow μs=static coeff. of friction…predicts force at the point in time when motion is initiated μd=dynamic coeff. of friction…predicts force required to maintain motion once it is initiated. μd<μs, these coeff. are dependent on the characteristics of the material 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Look at examples in Figure 9.1 (slip-stick motion) Tables 9.1 and 9.2. Lecture 11 – Friction and Flow Look at examples in Figure 9.1 (slip-stick motion) Tables 9.1 and 9.2. 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Lecture 11 – Friction and Flow angle of repose: The angle that a material makes with the horizontal when dropped into a bin or allowed to form a pile. 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Filling or emptying angle of repose Lecture 11 – Friction and Flow Filling or emptying angle of repose 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Lecture 11 – Friction and Flow Resistance to motion is quantified by… angle of internal friction Φi, or coefficient of internal friction μi μi = tan Φi 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Lecture 11 – Friction and Flow Predicting lateral forces on bins: For shallow bins (D>H) use Rankine equation For deep bins (H>>>D) use Janssen equation 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Lecture 11 – Friction and Flow Example: Estimate the lateral and vertical forces at the bottom of the wall of the following bin… Bin diameter = 17 m Fill depth = 40 m Material = wheat at 17%mc Concrete bin (wood float finish) 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Will work in class on Wednesday Problem1: If the bin of wheat in in the previous example is dried to 9% mc, calculate the increase or decrease in lateral pressure at the base of the bin. You will need to calculate the density using the appropriate formula from Chpt. 2, pg 25). Assume the depth will remain the same after drying. Indicate whether the pressure will increase or decrease. 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Will work in class on Wednesday Problem 2: The Omega Coop’s concrete silo is 90 ft. tall with an ID of 25 ft. (convert units!!!) Part a: Plot the horizontal pressure on the bin walls as a function of height from the ground surface. Assume the bottom of the bin is at the ground surface, the grain is 11.0% mc wheat and the bin is filled to 81 ft. Part b: Calculate the total vertical force at ground level 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials

Will work in class on Wednesday Problem 3: An elevator manager would like you design a concrete silo with a self-cleaning hopper bottom. The silo is located in Northwest Oklahoma. What is the angle of the hopper relative to a horizontal plane, what is the depth to the bottom of the hopper relative to ground level? What assumptions, if any, did you make? 9/22/2018 BAE2022/BAE4400 Physical Properties of Biological Materials