20 Questions
What is the purpose of a joint in machine elements?
fixing & limiting the relative motion of machine elements in certain directions while transferring power or force.
How are joints grouped based on physical principles?
Force closing (friction force), Form closing, Material closing (welding, soldering, gluing)
What are the steps involved in the design of joints?
- Definition of load case & constraints 2. Definition of mating surfaces 3. Calculation of the load per unit area 4. Comparison to ultimate strength 5. Analysis of extraordinaries
What are the elements of bolted joints?
The elements of bolted joints include load case definition, mating surface definition, load per unit area calculation, ultimate strength comparison, and analysis of extraordinaries.
What is the purpose of determining the minimum and maximum tension force in a bolt joint?
To ensure that the required torque can be achieved within a certain deviation.
How is the load per unit area determined in the context of bolt joints?
The load per unit area is determined by dividing the tension force by the load transmission surface area or the weakest cross-sectional area.
What safety factor is used for comparing the boundary state in bolt joints?
The safety factor 'n' is compared by dividing the actual load per unit area by the allowable load per unit area, or by dividing the actual stress by the allowable stress.
How is the stress in the threaded bolt after tightening the nut calculated?
The stress from the tension force is calculated using the formula Fv / Asigma, and the stress on the threads from tightening torque is calculated using the formula Mv / Kp.
What is the formula for the equivalent stress based on Mohr's theory?
The equivalent stress, σr, is calculated using the formula σ^2 + 4τ^2.
What is the formula for the load transmission surface (Ap) in bolt joints?
Ap = πi/4 * D^2
How is the weakest cross-sectional area (Atau) calculated in bolt joints?
Atau = d^3 * πm
How is the stress on the threads from tightening torque (τ) calculated in bolt joints?
The stress on the threads from tightening torque is calculated using the formula Mv / Kp, where Kp = 16 * d^3 * π.
What are the common bolt standards specified in the text?
ISO 898-1:2013, ISO 898-2:2009, and ISO 3506-1:1997
How are bolt materials classified, and what determines the groups?
Bolt materials are classified into groups such as 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 10.9, 12.9, and 14.9. The groups are determined by their tensile strength and yield strength.
What are the major types of threads mentioned in the text?
Mounting (sharp or vee) threads
What are the factors used to calculate frictional forces hindering motion during thread engagement?
Thread angle, pitch diameter, spatial friction cone angle, and conical friction coefficient
How is the essential perimetral force for nut tightening calculated?
It is calculated based on thread angle, pitch diameter, and cone angle.
What does the calculation of loosening perimetral force depend on?
It depends on whether the joint is self-locking or not.
How is tightening torque calculated?
It is calculated based on perimetral force and frictional torque on the bearing surface of the nut.
What is the Klein diagram mentioned in the text, and what is its purpose?
The Klein diagram is a tool for understanding the relationship between various forces and torques acting on threads during tightening and loosening.
Study Notes
- The text discusses various aspects of bolts and nuts, focusing on their materials, manufacturing processes, thread types, and forces acting on threads.
- ISO 898-1:2013, ISO 898-2:2009, and ISO 3506-1:1997 are common bolt standards specifying mechanical and material properties for carbon steel, alloy steel, austenitic steel, and stainless steel fasteners.
- Bolt materials include 3.6, 4.6, 4.8, 5.6, 5.8, 6.8, 8.8, 10.9, 12.9, and 14.9, with tensile strength and yield strength determining the groups. Nut strength groups correspond to required tensile strength for pairing with bolts.
- Manufacturing processes for bolts include plastic forming, upsetting the head and body, head forming, thread rolling, and more.
- Bolts can have force and form closing joints during fastening, which is achieved through tightening torque and clamping force.
- Two major types of threads are mounting (sharp or vee) threads, with ISO European and Whithworth (UK-US standard) designations.
- Threads can be classified based on gender (internal and external), designation (connection, sealing, fastening, special, and motion), handedness (right and left), pitch (coarse and fine), profile (trapezoidal, round, triangular, scalene, square, and rectangular), start (single-start and multi-start), and surface shape (cylindrical and conical).
- Frictional forces hindering motion during thread engagement can be calculated based on thread angle, pitch diameter, spatial friction cone angle, and conical friction coefficient.
- Essential perimetral force for nut tightening can be calculated based on thread angle, pitch diameter, and cone angle.
- Loosening perimetral force calculation depends on whether the joint is self-locking or not, with self-locking joints requiring a lower thread angle and non-self-locking joints having the nut twist off the bolt.
- Tightening torque is calculated based on perimetral force and frictional torque on the bearing surface of the nut.
- A Klein diagram is mentioned as a tool for understanding the relationship between various forces and torques acting on threads during tightening and loosening.
Test your knowledge about machine elements and bolt joints with this quiz. Explore the concepts of connections, relative movement limitations, and power transfer in machine elements.
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