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How Permissible Cycle Life is Calculated using FEA.

Updated: Mar 9, 2023

Introduction


Finite Element Analysis (FEA) has become an integral part of product design and engineering. By using FEA, engineers can simulate the behavior of products under various conditions, optimize designs, and ensure product reliability. In the context of pressure vessels, the ASME VIII-2 code requires that the Permissible Cycle Life be calculated to ensure the safety and reliability of the vessel. In this article, we will explore how FEA is used to calculate the Permissible Cycle Life of products and optimize their design. We will also discuss the significance of Permissible Cycle Life in FEA, and how it is related to the fatigue behavior of materials and structures. Finally, we will highlight NRP's expertise in using FEA to conduct experiments on a variety of structures, materials, and systems, resulting in improved product performance and reduced need for physical testing.


 

What is the Permissible Cycle Life in FEA?


One important aspect of product design is to ensure that the product will perform reliably and safely over its expected lifetime. In the context of pressure vessels, the ASME VIII-2 code requires that the Permissible Cycle Life be calculated to ensure the safety and reliability of the vessel. But what exactly is the Permissible Cycle Life in FEA?

Permissible Cycle Life is the maximum number of cycles that a material or structure can withstand before it fails due to fatigue.


Fatigue is a phenomenon that occurs when a material or structure is subjected to repeated loading and unloading, causing it to weaken over time. The Permissible Cycle Life is a crucial factor in product design, as it helps determine the maximum number of cycles that a product can withstand before failure.


In FEA, the Permissible Cycle Life is calculated using stress analysis and fatigue testing. Stress analysis involves simulating the behavior of a product under various loading conditions, such as changes in pressure or temperature. Fatigue testing involves subjecting a material or structure to repeated loading and unloading cycles to determine its fatigue behavior.


The Permissible Cycle Life is determined by comparing the stress analysis results to the fatigue behavior of the material or structure. The fatigue behavior is characterized by an S-N curve, which plots the stress amplitude against the number of cycles to failure. By comparing the stress levels in the stress analysis to the S-N curve, engineers can determine the Permissible Cycle Life for the material or structure.


Accurately calculating the Permissible Cycle Life is essential for ensuring the reliability and safety of products. If the Permissible Cycle Life is underestimated, the product may fail prematurely, leading to costly repairs or even catastrophic consequences. On the other hand, if the Permissible Cycle Life is overestimated, the product may be overdesigned, leading to unnecessary costs and weight.


In product design, the Permissible Cycle Life is used to optimize the design and ensure product reliability. By understanding the Permissible Cycle Life, engineers can make informed decisions about the material selection, design geometry, and operating conditions of a product. By optimizing the design, engineers can reduce the likelihood of premature failure and ensure the product meets performance and safety requirements.

In conclusion, the Permissible Cycle Life is a critical factor in product design and optimization.


By accurately calculating the Permissible Cycle Life using FEA and fatigue testing, engineers can ensure the reliability and safety of products over their expected lifetime. NRP is highly skilled in using FEA and fatigue testing to optimize designs and ensure the reliability of products. Our FEA consulting services have been utilized to conduct numerous FEA experiments on a variety of structures, materials, and systems, resulting in improved product performance and reduced need for physical testing.


 

How do you calculate Cycles Before Failure in FEA?


In product design and engineering, it is essential to ensure that products can withstand the expected number of cycles before failure. Failure due to fatigue can lead to costly repairs or even catastrophic consequences. To avoid these risks, engineers must accurately calculate the Cycles Before Failure for a product. But how do you calculate Cycles Before Failure using Finite Element Analysis (FEA)?


Cycles Before Failure is the maximum number of cycles that a material or structure can withstand before it fails due to fatigue. Fatigue is a complex phenomenon that depends on a variety of factors, such as the stress level, the stress range, and the frequency of loading. Cycles Before Failure is a crucial factor in product design, as it helps determine the expected lifetime of a product and its components.


In FEA, Cycles Before Failure is calculated using stress analysis and fatigue testing. Stress analysis involves simulating the behavior of a product under various loading conditions, such as changes in pressure or temperature. Fatigue testing involves subjecting a material or structure to repeated loading and unloading cycles to determine its fatigue behavior.

To calculate Cycles Before Failure, engineers must first establish the S-N curve for the material or structure. The S-N curve plots the stress amplitude against the number of cycles to failure. The stress amplitude is the difference between the maximum and minimum stresses that the material or structure experiences during the loading and unloading cycles.


Once the S-N curve is established, engineers can use it to determine the Cycles Before Failure for the material or structure. This is done by comparing the stress levels in the stress analysis to the S-N curve. If the stress levels exceed the endurance limit of the material or structure, the Cycles Before Failure will be reduced. If the stress levels are below the endurance limit, the Cycles Before Failure can be calculated based on the S-N curve.


Accurately calculating the Cycles Before Failure is essential for ensuring the reliability and safety of products. By understanding the Cycles Before Failure, engineers can make informed decisions about the material selection, design geometry, and operating conditions of a product. By optimizing the design, engineers can reduce the likelihood of premature failure and ensure the product meets performance and safety requirements.


In conclusion, Cycles Before Failure is a critical factor in product design and optimization. By accurately calculating the Cycles Before Failure using FEA and fatigue testing, engineers can ensure the reliability and safety of products over their expected lifetime. NRP is highly skilled in using FEA and fatigue testing to optimize designs and ensure the reliability of products. Our FEA consulting services have been utilized to conduct numerous FEA experiments on a variety of structures, materials, and systems, resulting in improved product performance and reduced need for physical testing.


 

Example


In product design and engineering, accurately calculating the life cycle is critical for ensuring the reliability and safety of a product. The ASME BPVC VIII-Div 2 code provides a framework for calculating the Permissible Cycle Life of pressure vessels using Finite Element Analysis (FEA) and fatigue testing.


Here are the steps involved in calculating the life cycle:


Step 1: Determine the Load History

The load history is based on the information in the User's Design Specification and the methods in ASME BPVC VIII-Div 2, Annex 5-B. It should include all significant operating loads and events that are applied to the component. If the exact sequence of loads is not known, alternatives should be examined to establish the most severe fatigue damage.


Step 2: Determine the Individual Stress-Strain Cycles

For a location in the component subject to a fatigue evaluation, determine the individual stress-strain cycles using the cycle counting methods in ASME BPVC VIII-Div 2, Annex 5-B. Define the total number of cyclic stress ranges in the histogram.


Step 3: Determine the Equivalent Stress Range

Determine the equivalent primary plus secondary plus peak stress range for the k cycle counted in Step 2.



Step 4: Determine the Effective Alternating Equivalent Stress Amplitude

Determine the effective alternating equivalent stress amplitude for the k cycle using the results from Step 3.


Step 5: Determine the Permissible Number of Cycles

Determine the permissible number of cycles, Nk, for the alternating equivalent stress computed in Step 4. Fatigue curves based on the materials of construction are provided in Annex 3-F.

Step 6: Determine the Fatigue Damage

Determine the fatigue damage for the k cycle, where the actual number of repetitions of the kth cycle is nk.

By following these steps, engineers can accurately calculate the life cycle of a product using FEA and fatigue testing.


By understanding the life cycle, engineers can make informed decisions about the material selection, design geometry, and operating conditions of a product. By optimizing the design, engineers can reduce the likelihood of premature failure and ensure the product meets performance and safety requirements.


NRP is highly skilled in using FEA and fatigue testing to optimize designs and ensure the reliability of products. Our FEA consulting services have been utilized to conduct numerous FEA experiments on a variety of structures, materials, and systems, resulting in improved product performance and reduced need for physical testing. We have a successful track record of using FEA to inform design decisions and improve overall product reliability.

Other failure calculation: Click Here


In conclusion, calculating the life cycle is a critical factor in product design and optimization. By accurately calculating the life cycle using FEA and fatigue testing, engineers can ensure the reliability and safety of products over their expected lifetime. NRP's expertise in FEA consulting services can help optimize product designs and reduce the need for physical testing. By utilizing our services, you can ensure that your products meet performance and safety requirements and are reliable over their expected lifetime.


 

Conclusion


Finite Element Analysis (FEA) has become an essential tool in product design and engineering. By using FEA, engineers can simulate the behavior of products under various conditions, optimize designs, and ensure product reliability. In the context of pressure vessels, the ASME BPVC VIII-Div 2 code requires that the Permissible Cycle Life be calculated to ensure the safety and reliability of the vessel.


In this article, we explored how FEA is used to calculate the Permissible Cycle Life and Cycles Before Failure of products and optimize their design. We also discussed the significance of accurately calculating these values for ensuring the reliability and safety of products. By understanding the Permissible Cycle Life and Cycles Before Failure, engineers can make informed decisions about the material selection, design geometry, and operating conditions of a product. By optimizing the design, engineers can reduce the likelihood of premature failure and ensure the product meets performance and safety requirements.


NRP is highly skilled in using FEA and fatigue testing to optimize designs and ensure the reliability of products. Our FEA consulting services have been utilized to conduct numerous FEA experiments on a variety of structures, materials, and systems, resulting in improved product performance and reduced need for physical testing. We have a successful track record of using FEA to inform design decisions and improve overall product reliability.


In summary, the Permissible Cycle Life and Cycles Before Failure are critical factors in product design and optimization. By accurately calculating these values using FEA and fatigue testing, engineers can ensure the reliability and safety of products over their expected lifetime. NRP's expertise in FEA consulting services can help optimize product designs and reduce the need for physical testing. By utilizing our services, you can ensure that your products meet performance and safety requirements and are reliable over their expected lifetime.


 

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