39 Questions
What is the main use of axles in the context of bending?
The main use of axles is bending, where bending moment causes normal stress.
What is the typical nature of the fatiguing stress in axles?
The nature of the fatiguing stress in axles is pulsating.
What are the main uses of shafts in the context of rotary bending and twisting?
The main uses of shafts are rotary bending and twisting.
What are the key considerations in the pre-planning and design of shafts?
The key considerations include determining the characteristic size of the shaft, defining the design in accordance with the installation and operating conditions, and controlling for reduced static use, deformation, critical speed, fatigue, and fracture.
What is the purpose of the Smith diagram?
The Smith diagram represents Wöhler curves at different mean stress values.
What is the purpose of reducing stress concentration in drilled holes in axles?
To reduce fatigue stresses and increase the lifetime of railway axles
What factors influence the endurance limit for machine elements?
The absolute size of the element, change in surface roughness (b2), and inhibit factors (βk) related to stress concentration points.
How is the load versus time relationship expressed when calculating fatigue stresses?
It can be broken down into sections with constant amplitudes
What principle is used to determine if a component will not fracture during recorded time?
Palmgren-Miner principle of linear cumulative damage
How is the surface roughness factor (b2) impacted?
The surface roughness factor (b2) is impacted by various surface machining processes and is plotted on the vertical axis of the Smith diagram.
What does the utilization factor (a) indicate in static or fatigue calculation?
The adequacy of the tested component
What does the inhibit factor (βk) account for?
The inhibit factor (βk) accounts for the fatigue-reducing effect of stress concentration points.
What factors are used to calculate the inhibit factor (βk)?
The shape factor (load concentration factor, ηk), sensitivity factor (dependent on material tensile strength), and the shape factor (load concentration factor, αk).
What happens if the utilization factor is greater than 1 in static stress or fatigue conditions?
The component fails
What must be determined in the block diagram for calculating components for static stress and fatigue?
Stress state and endurance limit state
What does the shape factor (αk) depend on?
The size, geometrical shape, and material, but not the material strength.
What are the sensitivity factors (ηk) for various materials?
Sensitivity factors (ηk) are provided for carbon steel, annealed steel, spring steel, and light metals, with values ranging from 0.4 to 1.0.
What are the three sections of the Wöhler-curve?
Low cycle fatigue, finite life, and high cycle
How can the inhibit factor be calculated for a shaft shoulder?
The inhibit factor can be calculated using the shape factor and tensile strength for a shaft shoulder in bending or twisting applications.
What is the purpose of the FKM engineering guidelines?
To provide a uniform view in calculation for structural elements
What does the finite life section of the Wöhler-curve involve?
Elastic deformation with possible plastic deformation at notches
What values are provided in standard tables for inhibit factors?
Inhibit factor values for keeways with vertical and horizontal cutter jaws, hub and shaft with no retessel, with interference fit, and with spline and gear joints are provided in standard tables.
How can the safety zone for machine elements be constructed?
The safety zone for machine elements can be constructed using the HAIGH diagram and the Smith diagram.
What does the FKM engineering guidelines not require knowledge of?
Endurance limit characteristics
At what possibility of survival is the calculation and checking done?
50%
How can stress concentration be reduced?
Stress concentration can be reduced by increasing local dimensions, forming good shape transitions, shading, and causing residual compression stress.
What is the quotient used to test the adequacy of a component in static or fatigue calculation?
Utilization factor (a)
What is the name of the German railway engineer who conducted systematic investigations of metal fatigue in train shafts and axles?
August Wöhler
What phenomenon leads to cracks appearing in components above a certain stress level, resulting in crack propagation and eventual failure?
Fatigue phenomenon
What type of stress are preloaded bolt joints under dynamic loads usually subjected to?
Fluctuating stress
What is used to model the probability of fracture in the statistical background of fatigue?
Gaussian distribution
What represents stress amplitudes acting in the fracture cross-section for different number of load cycles associated with a 10% probability of failure?
Wöhler curve
What type of stress do rotating shafts' keyways and grooves represent?
Stress concentration points
What does the Haigh diagram represent in relation to fatigue?
Fatigue limit of Wöhler curves at different mean stresses
What is the alternative representation of fatigue limit data for different mean stresses and amplitudes?
Smith diagram
What does the Wöhler curve consist of?
Low-cycle, finite life, and high-cycle fatigue sections
What type of stress does checking for fatigue deal with?
Sinusoidal stress
What is checked when calculating for endurance limit?
Applied stress is lower than the endurance limit
What is the cross-section of rotating shafts usually like?
Circle or ring
Study Notes
- Rotating shafts: Cross-section is usually a circle or ring, subjected to rotary folding bending stress.
- Fatigue phenomenon: Cracks appear in components above a certain stress level, leading to crack propagation and eventual failure.
- Rotating shafts: Keyways and grooves are stress concentration points.
- Checking for fatigue: Deals with sinusoidal stress with constant amplitudes, which can be traced back to this case through Fourier analysis.
- Preloaded bolt joints under dynamic loads: Subjected to pure pulsating stress or fluctuating stress between minimum and maximum values.
- Statistical background of fatigue: Lifetime deviations due to uncertainty of crack appearance time and propagation speed.
- Statistical background of fatigue: Gaussian distribution used to model probability of fracture, known as the normal distribution function.
- August Wöhler: German railway engineer who conducted systematic investigations of metal fatigue in train shafts and axles.
- Wöhler curve: Represents stress amplitudes acting in the fracture cross-section for different number of load cycles associated with a 10% probability of failure.
- Wöhler curve: Consists of low-cycle, finite life, and high-cycle fatigue sections.
- Calculation for endurance limit: Checks whether applied stress is lower than the endurance limit.
- Haigh diagram: Represents fatigue limit of Wöhler curves at different mean stresses.
- Smith diagram: Alternative representation of fatigue limit data for different mean stresses and amplitudes.
Test your knowledge of the Smith diagram and the construction of the approximate Smith chart according to the recommendation of the German engineering association VDI. This quiz covers the fatigue limit of Wöhler curves at different mean stress values and the construction of the Smith diagram.
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