CE336-05-Fatigue.ppt
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Fatigue refers to damage accumulated through repeated cyclic stresses over time. It is affected by factors like stress type/amplitude, surface finish, material properties, and environment. Fatigue life depends on the mean and amplitude of stresses based on relationships like the Goodman diagram. The Miner's rule states that the fraction of fatigue life consumed by stresses must be less than 1 to avoid failure. Fatigue tests involve repeated cyclic loads in tension, compression, bending, or other patterns to determine fatigue properties.
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FATIGUE AND FRACTURE MECHANICS.pptx
The document defines stress as a force per unit area within a material caused by external forces or temperature changes. It describes two main types of stress:
1) Tensile stress stretches the material from an applied pulling force.
2) Compressive stress reduces the material's volume from an applied squeezing force.
The document also defines strain as the amount of deformation or change in shape of a material under an applied force, divided by the original dimensions. Tensile strain is elongation during stretching, while compressive strain is deformation during squeezing.
Fatigue is failure from repeated cyclic loading, even at stress levels below the material's static strength. It accounts for about 90% of all metal
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1) Fatigue strength is reduced by stress concentrators like notches or holes. Stress concentrators can decrease fatigue limit.
2) Notch sensitivity depends on factors like notch severity, material properties, and stress level. It is measured by the notch sensitivity factor.
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This document discusses fatigue, which refers to mechanical failures caused by fluctuating stresses that are lower than the stress required to cause failure from a single application of stress. Fatigue contributes to approximately 90% of all mechanical service failures and can affect any component that experiences repeated motion or loading. The document outlines different types of stress cycles that can cause fatigue, and describes high-cycle fatigue which involves a large number of stress cycles in the elastic range, versus low-cycle fatigue which involves plastic deformation with each cycle. It also discusses how factors like mean stress, stress ratio, and material properties influence fatigue life and strength.
FATIGUE.pdf
This document discusses fatigue, which refers to failures caused by fluctuating stresses that are lower than the stress required to cause failure from a single application of stress. Fatigue contributes to approximately 90% of mechanical failures. There are two main types of fatigue: high-cycle fatigue involving a large number of cycles (over 105 cycles) and low-cycle fatigue involving plastic deformation. Several factors influence fatigue life including stress range, mean stress, surface condition, and material properties. Fatigue data is commonly presented using S-N curves or strain-life curves to relate the applied stress or strain to the number of cycles until failure.
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Fatigue is failure from repeated cyclic loading, even at stress levels below the material's static strength. It accounts for about 90% of all metal
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Fatigue ppt.pdf
1) Fatigue strength is reduced by stress concentrators like notches or holes. Stress concentrators can decrease fatigue limit.
2) Notch sensitivity depends on factors like notch severity, material properties, and stress level. It is measured by the notch sensitivity factor.
3) Larger components often have lower fatigue strength than lab specimens due to stress gradients caused by unavoidable stress concentrators in service. Fatigue life decreases with increasing critically stressed volume.
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This document discusses fatigue, which refers to mechanical failures caused by fluctuating stresses that are lower than the stress required to cause failure from a single application of stress. Fatigue contributes to approximately 90% of all mechanical service failures and can affect any component that experiences repeated motion or loading. The document outlines different types of stress cycles that can cause fatigue, and describes high-cycle fatigue which involves a large number of stress cycles in the elastic range, versus low-cycle fatigue which involves plastic deformation with each cycle. It also discusses how factors like mean stress, stress ratio, and material properties influence fatigue life and strength.
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This document discusses fatigue, which refers to failures caused by fluctuating stresses that are lower than the stress required to cause failure from a single application of stress. Fatigue contributes to approximately 90% of mechanical failures. There are two main types of fatigue: high-cycle fatigue involving a large number of cycles (over 105 cycles) and low-cycle fatigue involving plastic deformation. Several factors influence fatigue life including stress range, mean stress, surface condition, and material properties. Fatigue data is commonly presented using S-N curves or strain-life curves to relate the applied stress or strain to the number of cycles until failure.
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- Three factors are needed for fatigue failure: a maximum stress, stress variation, and sufficient number of cycles.
- Fatigue testing involves subjecting specimens to cyclic stresses and recording the number of cycles until failure to generate an S-N curve.
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2) Miner's cumulative damage theory assumes damage from different stress levels is independent and sums fractions of life used to predict failure. It is commonly used to analyze complex variable loading.
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Given:
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The document discusses fatigue, which is the weakening of a material when it is repeatedly loaded and unloaded. It defines fatigue strength as the load value below which the material would not yield for any number of loading cycles. It then lists several factors that can affect fatigue life, such as stress state, geometry, surface quality, material type, residual stresses, defects, environment and temperature. It also describes three common methods to determine fatigue life and characteristics of the fatigue process. Finally, it discusses S-N curves which are used to characterize the performance of materials under high-cycle fatigue by plotting cyclic stress against the number of cycles to failure.
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Fatigue is a type of failure that occurs in structures subjected to repeatedly applied loads, such as bridges and aircraft components. It can cause failure at stress levels lower than the material's static strength. Fatigue is responsible for approximately 90% of all metallic failures and occurs suddenly without warning. Fatigue failure is brittle-like and involves crack initiation and propagation. The fatigue behavior of materials is characterized by S-N curves, which relate the cyclic stress amplitude to the number of cycles to failure. Some materials exhibit a fatigue limit below which failure will not occur, while others do not have a fatigue limit. Surface treatments like shot peening can improve fatigue resistance by inducing compressive stresses near the surface.
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The document summarizes research from the Montana State University Fatigue Program on testing composite materials for wind turbine blades. It discusses recent findings on the effects of resin and fabric structure on fatigue properties. Environmental effects and how stresses impact moisture absorption in composites are also examined. Finite element analysis is used to model moisture diffusion under different stresses. The research aims to better understand fatigue and failure of composites under various loading conditions.Unit 3 Design of Fluctuating Loads
Given:
Stresses:
i) 350 N/mm2 for 85% of time
ii) 500 N/mm2 for 3% of time
iii) 400 N/mm2 for 12% of remaining time
Material: Plain carbon steel 50C
Using Miner's rule:
For stress i)
N1/Nf1 = 0.85
Where, N1 is no. of cycles component can withstand at stress 350 N/mm2
Nf1 is no. of cycles to failure at stress 350 N/mm2
Similarly, for other stresses:
N2/Nf2 = 0.03
N3/Nf3 = 0.12
Equ
Sabir shah
The document discusses fatigue, which is the weakening of a material when it is repeatedly loaded and unloaded. It defines fatigue strength as the load value below which the material would not yield for any number of loading cycles. It then lists several factors that can affect fatigue life, such as stress state, geometry, surface quality, material type, residual stresses, defects, environment and temperature. It also describes three common methods to determine fatigue life and characteristics of the fatigue process. Finally, it discusses S-N curves which are used to characterize the performance of materials under high-cycle fatigue by plotting cyclic stress against the number of cycles to failure.
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Philippine Edukasyong Pantahanan at Pangkabuhayan (EPP) Curriculum
(𝐓𝐋𝐄 𝟏𝟎𝟎) (𝐋𝐞𝐬𝐬𝐨𝐧 𝟏)-𝐏𝐫𝐞𝐥𝐢𝐦𝐬
𝐃𝐢𝐬𝐜𝐮𝐬𝐬 𝐭𝐡𝐞 𝐄𝐏𝐏 𝐂𝐮𝐫𝐫𝐢𝐜𝐮𝐥𝐮𝐦 𝐢𝐧 𝐭𝐡𝐞 𝐏𝐡𝐢𝐥𝐢𝐩𝐩𝐢𝐧𝐞𝐬:
- Understand the goals and objectives of the Edukasyong Pantahanan at Pangkabuhayan (EPP) curriculum, recognizing its importance in fostering practical life skills and values among students. Students will also be able to identify the key components and subjects covered, such as agriculture, home economics, industrial arts, and information and communication technology.
𝐄𝐱𝐩𝐥𝐚𝐢𝐧 𝐭𝐡𝐞 𝐍𝐚𝐭𝐮𝐫𝐞 𝐚𝐧𝐝 𝐒𝐜𝐨𝐩𝐞 𝐨𝐟 𝐚𝐧 𝐄𝐧𝐭𝐫𝐞𝐩𝐫𝐞𝐧𝐞𝐮𝐫:
-Define entrepreneurship, distinguishing it from general business activities by emphasizing its focus on innovation, risk-taking, and value creation. Students will describe the characteristics and traits of successful entrepreneurs, including their roles and responsibilities, and discuss the broader economic and social impacts of entrepreneurial activities on both local and global scales.
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CE336-05-Fatigue.ppt
- 2. Fatigue Definition: Damage accumulated through the application of repeated stress cycles Variable amplitude loadings cause different levels of fatigue Fatigue is cumulative through the life of an engineering element
- 3. Factors Affecting Fatigue Life Loading Conditions Type of stress Stress amplitude, mean value Condition of Specimen/Structural Member Stress concentrations Surface finish Material Thermal history (e.g. grain size in metals) Environmental conditions Temperature Corrosion effects
- 5. Effect of Mean Stresses sa sm=0 sa sm>0 sult Mean Stresses reduce the stress range No mean stress
- 6. Stress Amplitude vs. Mean Goodman Relationship: lower the mean stresses, the greater the allowable stress amplitude for the same life. 1 u m f a s s s s sa sm sf su
- 7. Example: Goodman Diagram If sf=su/2, sm=su/2, What is the max and min s that can be applied? sa sm su/2sf su su/4sf su/2sm smin= su/4 smax= 3su/4
- 8. Stress vs. Number of Cycles S-N Diagram Lower mean stress
- 9. Miner’s Rule Damage from variable loadings is related to the life consumed by number of cycles at each particular STRESS RANGE. The summation of life consumed at each stress range must be less than 1 to avoid failure. where: ni = number of repetitions applied at si Nfi = number of repetitions to cause failure at a stress range, si (ni < Nfi) S ni/Nfi 1
- 10. Example problem - Miner’s Rule SNi/Nfi = 900/10,000 + 50/500 = 0.09 + 0.10 = 0.19 0.19 < 1.0 OK Used 19% of fatigue life, 81% remains Stress Range, si (ksi) No. Applied Cycles, Ni No. Cycles to Failure,Nfi 3 900 10,000 5 50 500 Log N 5 500 3 10,000
- 11. Fatigue tests 2. Tension- Compression Loading Patterns: 1. Reverse stresses, + to - 2. Alternate zero to some maximum 3. Alternate above some base value V M 1. Beam Fatigue M 2c smax = Mc/I 3. Others