Lecture 11Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Will work in class on WednesdaySlide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 2801/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials1Lecture 11•Test next Wednesday (2/24): covers material through Friday•Lab this Wednesday: tension and compression01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials2Lecture 11 - Rheology01/14/19 BAE2023 Physical Properties of Biological Materials Fricton and Flow3Chapter 9 Page 239 – 256Friction of Solids and Flow of Granular SolidsLecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials4•Tribology: the study of friction and interaction between solids with relative motion between 2 surfaces in contact with each other.Lecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials5•original Coulomb’s law:–proportional to normal force (load)–independent of area of sliding surfaces–Independent of velocity–Depends on materials in contacttnF =force acting in opposite direction of relative motionF =normal force exerted on the object = static or dynamic coefficient of frictiont nF Fmm=Lecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials6• 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 materialLecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials7•Look at examples in Figure 9.1 (slip-stick motion)•Tables 9.1 and 9.2. Lecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials8• angle of repose:–The angle that a material makes with the horizontal when dropped into a bin or allowed to form a pile.Lecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials9• Filling or emptying angle of repose•Empting > FillingLecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials10• Resistance to motion is quantified by…–angle of internal friction Φi, or –coefficient of internal friction μi–μi = tan ΦiLecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials11• Flow Patterns: Fig. 9.3•Funnel Flow•Mass Flow•Expanded FlowLecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials12•Predicting lateral forces on bins:–For shallow bins (D>H) use Rankine equation–For deep bins (H>>>D) use Janssen equationLecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials13•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)Lecture 11 – Friction and Flow01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials14Will work in class on WednesdayProblem1: 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.01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials15Problem 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 levelWill work in class on Wednesday01/14/19 BAE2022/BAE4400 Physical Properties of Biological Materials16Problem 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?Will work in class on Wednesday01/14/19 BAE2023 Physical Properties of Biological Materials Fricton and Flow17•original Coulomb’s law:–proportional to normal force (load)–independent of area of sliding surfaces–Independent of velocity–Depends on materials in contacttnF =force acting in opposite direction of relative motionF =normal force exerted on the object = static or dynamic coefficient of frictiont nF Fmm=Lecture 11 – Friction and Flow01/14/19 BAE2023 Physical Properties of Biological Materials Fricton and Flow18•Tribology: the study of friction and interaction between solids with relative motion between 2 surfaces in contact with each other.Lecture 11 – Friction and Flow01/14/19 BAE2023 Physical Properties of Biological Materials Fricton and Flow19• 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 materialLecture 11 – Friction and Flow01/14/19 BAE2023 Physical Properties of Biological Materials Fricton and Flow20•Look at examples in Figure 9.1 (slip-stick motion)•Tables 9.1 and 9.2. Lecture 11 – Friction and Flow01/14/19 BAE2023 Physical Properties of Biological Materials Fricton and Flow21• angle of repose:–The angle that a material makes with the horizontal when dropped into a bin or allowed to form a pile.Lecture 11 – Friction and Flow01/14/19 BAE2023 Physical Properties of Biological Materials Fricton and Flow22• Filling or emptying angle of reposeLecture 11 – Friction and Flow01/14/19 BAE2023 Physical Properties of Biological Materials Fricton and Flow23• Resistance to motion is quantified by…–angle of internal friction Φi, or –coefficient of internal friction μi–μi = tan ΦiLecture 11 – Friction and
View Full Document
Unlocking...