Nickel-Based Bolt Design Using Damage Tolerance Theory
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Solution Overview
Problem
Conventional design methods for nickel-based high-temperature bolts, which rely on strength theories, fail to account for fracture toughness, leading to unexpected fractures and economic losses due to inadequate resistance to fracture, especially in long-term high-temperature applications.
Innovation Solution
A design method based on damage tolerance theory that includes acquiring operating parameters, selecting materials, determining pretension stress, calculating residual and thermal stresses, and ensuring the maximum allowable crack dimension to prevent crack propagation, thereby ensuring the bolts' safety during their service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional strength-based design methods are used for nickel-based high-temperature bolts, then the bolts achieve high strength and anti-relaxation properties, but they exhibit low resistance to fracture and inadequate fracture toughness in long-term high-temperature service
Solution Approach 1:
The patent changes the design parameter from conventional strength-based criteria to fracture toughness-based criteria. It introduces time-dependent fracture toughness parameters (KIC(t)) to account for the degradation of fracture resistance during long-term high-temperature service, thereby resolving the contradiction between maintaining high strength and ensuring adequate fracture resistance
Solution Approach 2:
The patent performs preliminary assessment of fracture toughness at the design stage by evaluating time-dependent fracture toughness parameters and conducting fracture risk assessment before the bolts are put into service. This allows designers to predict potential fracture issues and adjust design parameters proactively, rather than waiting for actual service failures
2Strength
If nickel-based alloys with high strength are selected for high-temperature bolt applications, then the bolts meet strength requirements, but fracture incidents occur due to reduced fracture toughness after long-term service
Solution Approach 1:
The patent establishes a feedback mechanism by continuously monitoring the time-dependent fracture toughness degradation during the bolt's service life. It uses fracture mechanics equations to predict crack growth and updates the fracture risk assessment based on accumulated service time and operating conditions, allowing for predictive maintenance and replacement before catastrophic failure occurs
Solution Approach 2:
The patent applies a more conservative design approach by using time-dependent fracture toughness parameters that account for the worst-case scenario of complete property degradation over the entire service life. This excessive caution in design ensures that even if the bolts operate at the limit of their capabilities, they will not suffer catastrophic fracture
3Ease of manufacture
If conventional design procedures are followed without considering fracture toughness, then the design process is simple and follows established protocols, but fracture incidents cause shutdowns and enormous economic losses
Solution Approach 1:
The patent segments the design process into distinct modules: material selection based on fracture toughness, stress analysis using fracture mechanics equations, fracture risk assessment, and service life prediction. This modular approach maintains design simplicity while systematically incorporating fracture toughness considerations, making the complex assessment manageable and repeatable
Data Source
AI summary
The invention relates to a design method of high-temperature nickel-based bolts based on damage tolerance theory, comprising the following steps: S1: acquiring operating parameters for the design; S2: selecting a material for bolts; S3: acquiring mechanical properties of the materials; S4: determining a pretension stress σp of a single bolt; S5: determining the service stress σs under the steady state; S6: determining the number n, the effective cross-section area A and the distribution of bolts; S7: determining a maximum allowable crack dimension; S8: calculating the maximum allowable service stress σth using the crack propagation threshold Kth at the design temperature; S9: comparing the service stress σs and the maximum allowable service stress σth, if σs is smaller than σth, then the bolts are safe in the design life; otherwise, return to step S4 and reduce the pretension stress σp.