Thermal shock is a type of rapidly transient mechanical load. By definition, it is a mechanical load caused by a rapid change of temperature of a certain point. It can be also extended to the case of a

thermal gradient A temperature gradient is a physical quantity that describes in which direction and at what rate the temperature changes the most rapidly around a particular location. The temperature gradient is a dimensional quantity expressed in units of degre ...

, which makes different parts of an object expand by different amounts. This differential expansion can be more directly understood in terms of

strain Strain may refer to: Science and technology * Strain (biology), variants of plants, viruses or bacteria; or an inbred animal used for experimental purposes * Strain (chemistry), a chemical stress of a molecule * Strain (injury), an injury to a mu ...

, than in terms of

stress Stress may refer to: Science and medicine * Stress (biology), an organism's response to a stressor such as an environmental condition * Stress (linguistics), relative emphasis or prominence given to a syllable in a word, or to a word in a phrase ...

, as it is shown in the following. At some point, this stress can exceed the

tensile strength Ultimate tensile strength (UTS), often shortened to tensile strength (TS), ultimate strength, or F_\text within equations, is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials t ...

of the material, causing a crack to form. If nothing stops this crack from propagating through the material, it will cause the object's structure to fail. Failure due to thermal shock can be prevented by: # Reducing the thermal gradient seen by the object, by changing its temperature more slowly or increasing the material's

thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

# Reducing the material's coefficient of

thermal expansion Thermal expansion is the tendency of matter to change its shape, area, volume, and density in response to a change in temperature, usually not including phase transitions. Temperature is a monotonic function of the average molecular kinetic ...

# Increasing its strength # Introducing built-in compressive stress, as for example in

tempered glass Tempered or toughened glass is a type of safety glass processed by controlled thermal or chemical treatments to increase its strength compared with normal glass. Tempering puts the outer surfaces into compression and the interior into tensi ...

# Decreasing its

Young's modulus Young's modulus E, the Young modulus, or the modulus of elasticity in tension or compression (i.e., negative tension), is a mechanical property that measures the tensile or compressive stiffness of a solid material when the force is applied le ...

# Increasing its

toughness In materials science and metallurgy, toughness is the ability of a material to absorb energy and plastically deform without fracturing.plasticity or

phase transformation In chemistry, thermodynamics, and other related fields, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic states of ...

) or crack deflection

Effect on materials

Borosilicate glass Borosilicate glass is a type of glass with silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficients of thermal expansion (≈3 × 10−6 K−1 at 20 °C), m ...

is made to withstand thermal shock better than most other glass through a combination of reduced expansion coefficient and greater strength, though

fused quartz Fused quartz, fused silica or quartz glass is a glass consisting of almost pure silica (silicon dioxide, SiO2) in amorphous (non-crystalline) form. This differs from all other commercial glasses in which other ingredients are added which change ...

outperforms it in both these respects. Some

glass-ceramic Glass-ceramics are polycrystalline materials produced through controlled crystallization of base glass, producing a fine uniform dispersion of crystals throughout the bulk material. Crystallization is accomplished by subjecting suitable glasses to ...

materials (mostly in the lithium aluminosilicate (LAS) system) include a controlled proportion of material with a negative expansion coefficient, so that the overall coefficient can be reduced to almost exactly zero over a reasonably wide range of temperatures. Among the best thermomechanical materials, there are alumina,

zirconia Zirconium dioxide (), sometimes known as zirconia (not to be confused with zircon), is a white crystalline oxide of zirconium. Its most naturally occurring form, with a monoclinic crystalline structure, is the mineral baddeleyite. A dopant sta ...

tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

alloys,

silicon nitride Silicon nitride is a chemical compound of the elements silicon and nitrogen. is the most thermodynamically stable and commercially important of the silicon nitrides, and the term "silicon nitride" commonly refers to this specific composition. It ...

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal s ...

, boron carbide, and some stainless steels. Reinforced carbon-carbon is extremely resistant to thermal shock, due to

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on lar ...

's extremely high thermal conductivity and low expansion coefficient, the high strength of

carbon fiber Carbon fiber-reinforced polymers (American English), carbon-fibre-reinforced polymers (Commonwealth English), carbon-fiber-reinforced plastics, carbon-fiber reinforced-thermoplastic (CFRP, CRP, CFRTP), also known as carbon fiber, carbon compo ...

, and a reasonable ability to deflect cracks within the structure. To measure thermal shock, the

impulse excitation technique The impulse excitation technique (IET) is a non-destructive material characterization technique to determine the elastic properties and internal friction of a material of interest. It measures the resonant frequencies in order to calculate the You ...

proved to be a useful tool. It can be used to measure Young's modulus,

Shear modulus In materials science, shear modulus or modulus of rigidity, denoted by ''G'', or sometimes ''S'' or ''μ'', is a measure of the elastic shear stiffness of a material and is defined as the ratio of shear stress to the shear strain: :G \ \stackre ...

Poisson's ratio In materials science and solid mechanics, Poisson's ratio \nu ( nu) is a measure of the Poisson effect, the deformation (expansion or contraction) of a material in directions perpendicular to the specific direction of loading. The value of Po ...

and

damping Damping is an influence within or upon an oscillatory system that has the effect of reducing or preventing its oscillation. In physical systems, damping is produced by processes that dissipate the energy stored in the oscillation. Examples in ...

coefficient in a non destructive way. The same test-piece can be measured after different thermal shock cycles and this way the deterioration in physical properties can be mapped out.

Thermal shock resistance

Thermal shock resistance measures can be used for material selection in applications subject to rapid temperature changes. A common measure of thermal shock resistance is the maximum temperature differential,

\Delta T

, which can be sustained by the material for a given thickness.

Strength-controlled thermal shock resistance

Thermal shock resistance measures can be used for material selection in applications subject to rapid temperature changes. The maximum temperature jump, sustainable by a material can be defined for strength-controlled models by:

B\Delta T = \frac

where

\sigma_f

is the failure stress (which can be yield or fracture stress),

\alpha

is the coefficient of thermal expansion,

E

is the Young's modulus, and

B

is a constant depending upon the part constraint, material properties, and thickness.

B = \frac

where

C

is a system constrain constant dependent upon the Poisson's ratio, and

A

is a non-dimensional parameter dependent upon the Biot number,

C = \begin
1 & \text \\
(1-\nu) & \text \\
(1-2\nu) & \text
\end

A

may be approximated by:

A = \frac = \frac

where

H

is the thickness,

h

is the heat transfer coefficient, and

k

is the

Perfect heat transfer

If perfect heat transfer is assumed, the maximum heat transfer supported by the material is:

\Delta T = A_1\frac

A_1 \approx 1

for cold shock in plates *

A_1 \approx 3.2

for hot shock in plates A material index for material selection according to thermal shock resistance in the fracture stress derived perfect heat transfer case is therefore:

\frac

Poor heat transfer

For cases with poor heat transfer the maximum heat differential supported by the material is:

\Delta T = A_2\frac\frac = A_2\frac\frac

A_2 \approx 3.2

for cold shock *

A_2 \approx 6.5

for hot shock In the poor heat transfer case, a higher heat transfer coefficient is beneficial for thermal shock resistance. The material index for the poor heat transfer case is often taken as:

\frac

According to both the perfect and poor heat transfer models, larger temperature differentials can be tolerated for hot shock than for cold shock.

Fracture toughness controlled thermal shock resistance

In addition to thermal shock resistance defined by material fracture strength, models have also been defined within the fracture mechanics framework. Lu and Fleck produced criteria for thermal shock cracking based on fracture toughness controlled cracking. The models were based on thermal shock in ceramics (generally brittle materials). Assuming an infinite plate and mode I cracking, the crack was predicted to start from the edge for cold shock, but the center of the plate for hot shock. Cases were divided into perfect and poor heat transfer to further simplify the models.

Perfect heat transfer

The sustainable temperature jump decreases, with increasing convective heat transfer (and therefore larger Biot number). This is represented in the model shown below for perfect heat transfer

\Delta T = A_3 \frac

where

K_

is the mode I fracture toughness,

E

is the Young's modulus,

\alpha

is the thermal expansion coefficient, and

H

is half the thickness of the plate. *

A_3 \approx 4.5

for cold shock *

A_4 \approx 5.6

for hot shock A material index for material selection in the fracture mechanics derived perfect heat transfer case is therefore:

\frac

Poor heat transfer

For cases with poor heat transfer, the Biot number is an important factor in the sustainable temperature jump.

\Delta T = A_4 \frac\frac

Critically, for poor heat transfer cases, materials with higher thermal conductivity, , have higher thermal shock resistance. As a result a commonly chosen material index for thermal shock resistance in the poor heat transfer case is:

\frac

Kingery thermal shock methods

The temperature difference to initiate fracture has been described by William David Kingery to be:

\Delta T_c = S \frac \frac = \frac

where

S

is a shape factor,

\sigma^*

is the fracture stress,

k

is the thermal conductivity,

E

is the Young's modulus,

\alpha

is the coefficient of thermal expansion,

h

is the heat transfer coefficient, and

R'

is a fracture resistance parameter. The fracture resistance parameter is a common metric used to define the thermal shock tolerance of materials.

R' = \frac

The formulas were derived for ceramic materials, and make the assumptions of a homogeneous body with material properties independent of temperature, but can be well applied to other brittle materials.

Testing

Thermal shock testing exposes products to alternating low and high temperatures to accelerate failures caused by temperature cycles or thermal shocks during normal use. The transition between temperature extremes occurs very rapidly, greater than 15 °C per minute. Equipment with single or multiple chambers is typically used to perform thermal shock testing. When using single chamber thermal shock equipment, the products remain in one chamber and the chamber air temperature is rapidly cooled and heated. Some equipment uses separate hot and cold chambers with an elevator mechanism that transports the products between two or more chambers. Glass containers can be sensitive to sudden changes in temperature. One method of testing involves rapid movement from cold to hot water baths, and back.ASTM C149 — Standard Test Method for Thermal Shock Resistance of Glass Containers

Examples of thermal shock failure

* Hard rocks containing ore veins such as

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...

were formerly broken down using

fire-setting Fire-setting is a method of traditional mining used most commonly from Prehistory, prehistoric times up to the Middle Ages. Fires were set against a rock face to heat the Rock (geology), stone, which was then doused with liquid, causing the sto ...

, which involved heating the rock face with a wood fire, then quenching with water to induce crack growth. It is described by Diodorus Siculus in Egyptian

gold mine Gold Mine may refer to: * Gold Mine (board game) *Gold Mine (Long Beach), an arena *"Gold Mine", a song by Joyner Lucas from the 2020 album ''ADHD Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder characteri ...

Pliny the Elder Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, naturalist and natural philosopher, and naval and army commander of the early Roman Empire, and a friend of the emperor Vespasian. He wrote the encyclopedic ' ...

, and

Georg Agricola Georgius Agricola (; born Georg Pawer or Georg Bauer; 24 March 1494 – 21 November 1555) was a German Humanist scholar, mineralogist and metallurgist. Born in the small town of Glauchau, in the Electorate of Saxony of the Holy Roman Emp ...

. * Ice cubes placed in a glass of warm water crack by thermal shock as the exterior surface increases in temperature much faster than the interior. The outer layer expands as it warms, while the interior remains largely unchanged. This rapid change in volume between different layers creates stresses in the ice that build until the force exceeds the strength of the ice, and a crack forms, sometimes with enough force to shoot ice shards out of the container. * Incandescent bulbs that have been running for a while have a very hot surface. Splashing cold water on them can cause the glass to shatter due to thermal shock, and the bulb to implode. * An antique cast iron cookstove is a simple iron box on legs, with a cast iron top. A wood or coal fire is built inside the box and food is cooked on the top outer surface of the box, like a griddle. If a fire is built too hot, and then the stove is cooled by pouring water on the top surface, it will crack due to thermal shock. * It is widely hypothesized that following the

casting Casting is a manufacturing process in which a liquid material is usually poured into a mold, which contains a hollow cavity of the desired shape, and then allowed to solidify. The solidified part is also known as a ''casting'', which is ejected ...

of the Liberty Bell, it was allowed to cool too quickly which weakened the integrity of the bell and resulted in a large crack along the side of it the first time it was rung. Similarly, the strong gradient of temperature (due to the dousing of a fire with water) is believed to cause the breakage of the third

Tsar Bell The Tsar Bell (russian: Царь–колокол; ), also known as the Tsarsky Kolokol, Tsar Kolokol III, or Royal Bell, is a , bell on display on the grounds of the Moscow Kremlin. The bell was commissioned by Empress Anna Ivanovna, niece o ...

. * Thermal shock is a primary contributor to

head gasket In an internal combustion engine, a head gasket provides the seal between the engine block and cylinder head(s). Its purpose is to seal the combustion gases within the cylinders and to avoid coolant or engine oil leaking into the cylinders. Leak ...

failure in internal combustion engines.

References

{{DEFAULTSORT:Thermal Shock Materials degradation Laser science Heat transfer Temperature

Effect on materials

Thermal shock resistance

Strength-controlled thermal shock resistance

Perfect heat transfer

Poor heat transfer

Fracture toughness controlled thermal shock resistance

Perfect heat transfer

Poor heat transfer

Kingery thermal shock methods

Testing

Examples of thermal shock failure

See also

References