Thermal Shock Analysis
Thermal Shock Analysis: Theoretical Foundations
Thermal Shock
Professor, what is thermal shock?
Thermal stress generated by rapid temperature changes. Typical in ceramics, glass, refractories. When the surface is rapidly cooled, tensile stress occurs on the surface → cracking.
Thermal Shock Resistance
Kingsley's R factor: $R = \sigma_f(1-\nu)/(E\alpha)$. Higher R indicates better thermal shock resistance.
Summary
Fracture Mechanics of Thermal Shock: Thermal Shock Coefficient R
Thermal Shock is instantaneous thermal stress caused by rapid temperature changes, a primary failure mechanism causing cracks in ceramics. Hasselman (1969, GE R&D Center) defined thermal shock resistance as R=σf(1−ν)/(Eα) (first thermal shock resistance, critical temperature difference for crack initiation). High-toughness ceramic ZrO₂ (PSZ) has an R about 3 times that of Al₂O₃, one reason it's used for insulation/TBC coatings. Glass (soda-lime) has an R of about 80°C, and quenching experiments have demonstrated a 50% failure probability when dropped into 100°C water.
Computational Methods for Thermal Shock Analysis
FEM for Thermal Shock
1. Transient Heat Conduction Analysis — Temperature distribution changing over time
2. Structural Analysis at Each Time Step — Temperature distribution → thermal stress
3. Identify Time of Maximum Stress — When temperature gradient is maximum
Summary
Procedure for Transient Thermal Stress Analysis
Transient analysis for thermal shock follows the flow: ① Set boundary conditions for instantaneous cooling/heating (surface heat transfer coefficient h value is dominant), ② Time-integrate the transient heat conduction equation using an implicit method (Crank-Nicolson method), ③ Calculate thermal strain + elastic stress from the temperature distribution at each time step. For ceramics, low thermal conductivity creates temperature differences of several hundred °C between surface and interior, causing rapid stress changes (tension/compression) on the surface. This process can be automated with Ansys Transient Thermal → Static Structural coupled analysis, with a recommended time step of 1/10 or less of the thermal diffusion time (L²/α).
Thermal Shock Analysis in Practice
Practical Checklist
Thermal Shock Evaluation for Nuclear Reactor Emergency Core Cooling
During activation of a nuclear reactor's Emergency Core Cooling System (ECCS), low-temperature cooling water (~20°C) is rapidly injected into the high-temperature reactor pressure vessel (~320°C). This 300°C temperature difference thermal shock (Pressurized Thermal Shock, PTS) generates transient tensile stress up to 400 MPa on the vessel wall. US NRC Regulatory Guide 1.99Rev.2 requires fracture toughness evaluation considering irradiation embrittlement (RTNDT transition temperature). Evaluation combining Westinghouse's HEATH analysis code with 3D-FEM has become an international standard. In Japan, Toshiba Energy Systems & Solutions conducts equivalent evaluations.
Thermal Shock Analysis: Software & Solver Comparison
Tools
All FEM solvers support thermal-structural coupling. No difference.
Solver-Specific Approach Comparison for Thermal Shock Analysis
Methods for thermal shock analysis differ significantly by solver. ABAQUS/Explicit can track contact/fracture using explicit methods and was adopted for delamination analysis of GE's gas turbine thermal barrier coatings (TBC). ANSYS tracks crack growth with ADPCM (Adaptive Thermo-Mechanical Coupling) mesh. MSC Nastran has provided a Thermo-Mechanical Fatigue module specialized for 1,000+ cycles since 2019.
Advanced Technology
Advanced
Fracture Mechanics of Thermal Shock: Ceramic Quenching Experiments
Thermal shock fracture in ceramics was quantified by Kingery's 1955 alumina specimen quenching experiment. Quenching from 900°C into water initiates cracking at ΔT ≥ 200°C, and the critical temperature difference can be predicted by the product of Biot number and fracture toughness KIC. In modern solar panel manufacturing, thermal shock during quenching is analyzed with ABAQUS/Explicit, and cooling rate designs achieving 95% survival rate for Si3N4 substrates with KIC=2.0 MPa√m have been commercialized.
Thermal Shock Analysis: Common Issues & Debugging
Troubles
Accuracy Issue in Setting Heat Transfer Coefficient (h value)
The surface heat transfer coefficient h value setting greatly influences thermal shock analysis results. In quenching experiments (e.g., dropping high-temperature ceramic into water), boiling heat transfer occurs, with h = 10,000–50,000 W/m²K in nucleate boiling region and h = 200–400 W/m²K in film boiling region—a difference of over 100 times. Assuming a constant h value can cause maximum thermal stress to deviate by over 50%, as shown in a 2015 report by the Japan Fine Ceramics Center (JFCC, Nagoya). Identifying h by combining experimental IR thermometer data with inverse heat conduction analysis is key to improving accuracy.
Related Topics
Experience the theory firsthand with the interactive simulator for this field
All Simulators