ASM Metals HandBook Vol. 8 - Mechanical Testing and Evaluation

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146 HB 0.08

0.57

SAE980X

Prestrained,

225 HB

569 82.5 2658 385.5

0.25 1185 171.8 -

0.10

0.09

0.48

1006 Hot rolled,

85 HB

236 34.2 1351 196.0

0.28 802 116.3 -

0.12

0.48

0.52

1020 Annealed,

108 HB

233 33.8 1206 174.9

0.26 850 123.3 -

0.12

0.44

0.51

1045 225 HB 402 58.3 1178 170.8

0.17 960 139.2 -

0.08

0.50

0.52

1045 Q&T, 390

842 122.1

1492 216.4

0.09 1408 204.2 -

0.07

1.51

0.85

1045 Q&T, 500

1303

189.0

4634 672.1

0.2 2888 418.9 -

0.09

0.23

0.56

1045 Q&T, 705

2255

327.0

4264 618.4

0.1 2416 350.4 -

0.07

0.002

0.47

10B21 Q&T, 320

691 100.2

990 143.6

0.06 1036 150.3 -

0.04

4.33

0.85

1080 Q&T, 421

870 126.2

3177 460.8

0.21 2364 342.9 -

0.10

0.51

0.59

4340 Q&T, 350

797 115.6

1863 270.2

0.14 1944 282.0 -

0.10

1.22

0.73

4340 Q&T, 410

876 127.0

1950 282.8

0.13 1898 275.3 -

0.09

0.67

0.64

5160 Q&T, 440

1070

155.2

2432 352.7

0.13 2068 300.0 -

0.08

9.56

1.05

8630 Q&T, 254

603 87.5 961 139.4

0.08 1049 152.1 -

0.11

0.21 -

0.86

(a) Q&T, quenched and tempered.

(b) E, elastic modulus; S

, yield strength; S

, tensile strength; σ

, true fracture stress; ε

, true fracture strain;

%RA, percent reduction in area. K and n per Eq 1.

cyclic yield strength; K′ cyclic strength coefficient; n′ cyclic strain hardening exponent; see also Eq 3 for

definitions of b and c.

Source: Ref 1

Table 2 Monotonic and cyclic stress-strain properties of selected aluminum alloys

Elastic

modulus

(E)

Yield

strength

)

Tensile

strength

)

Strength

coefficient

(K)

True

fracture

stress (σ

)

Alloy Condition

GPa 10

ksi MPa ksi MPa ksi MPa ksi

Strain

hardening

exponent

(n)

Reduction

in area,

MPa ksi

True

fracture

strain

(ε

)

Monotonic properties

(a)

1100 As received 69 10 97 14 110 16 … … … 88 … …

2.1

2014 T6 temper 73 10.6 462 67 510 74 … … … 35 627 91

0.42

2024 T351 temper 70 10.2 303 44 476 69 807 117 0.20 35 634 92

0.38

2024 T4 temper 73 10.6 T 688

C 303

T 55

C 44

469 68 T 455

C 634

T 66

C 92

T 32

C 0.17

25 558 81

0.43

2219 T851 temper 71 10.3 359 52 469 68 … … … … … …

0.28

5086 F temper 70 10.1 207 30 310 45 … … … … … …

0.36

5182 O temper 72 10.5 L 110

T 131

L 16

T 19

L 303

T 338

L 44

T 49

… … … L 37

T 44

393 57

L 0.46

T 0.58

5454 O Temper 69 10 138 20 248 36 … … … 44 365 53

0.58

5454 10% cold rolled 69 10 … … … … … … … … … …

…

5454 20% cold rolled 69 10 … … … … … … … … … …

…

5456 H311 temper 69 10 234 34 400 58 … … … 35 524 76

0.42

6061 T651 temper 69 10 290 42 310 45 365 53 0.042 58 469 68

0.86

7075 T6 temper 71 10.3 469 68 579 84 827 120 0.113 33 745 108

0.41

7075 T73 temper 72 10.4 414 60 483 70 … 86 0.054 23 579 84 0.26

Cyclic

yield

strength

(S′

)

Cyclic

strength

exponent

(K′)

Cyclic true

fracture

stress (σ′

)

Alloy

Condition

MPa ksi MPa ksi

Cyclic

strain

hardening

exponent

(n′)

MPa ksi

b Cyclic

true

fracture

strain

(ε′

)

Cyclic properties

(b)

1100 As received 55 8 159 23 0.17 193 28 -

0.106

1.8

-0.69

2014 T6 temper 448 65 703 102 0.073 786 114 -

0.081

0.85

-0.86

2024 T351 temper

448 65 786 114 0.09 1014 147 -0.11 0.21

-0.52

2024 T4 temper 427 62 655 95 0.065 1103 160 -

0.124

0.22

-0.59

2219 T851 temper

331 48 793 115 0.14 834 121 -0.11 1.33

0.079

5086 F temper 296 43 600 87 0.11 572 83 -

0.092

0.69

-0.75

5182 O temper 296 43 469 68 0.075 841 122 -

0.137

1.76

-0.92

5454 O temper 234 34 400 58 0.084 565 82 -

0.116

1.78

-0.85

5454 10% cold

rolled

234 34 427 62 0.098 565 82 -

0.108

0.48

-0.67

5454 20% cold

rolled

255 37 407 59 0.081 565 82 -

0.103

1.75

-0.80

5456 H311

temper

352 51 600 87 0.086 724 105 -0.11 0.46

-0.67

6061 T651 temper

296 43 538 78 0.096 634 92 -

0.099

0.92

-0.78

7075 T6 temper 517 75 965 140 0.10 1317 191 -

0.126

0.19

-0.52

7075 T73 temper 400 58 510 74 0.032 800 116 -

0.098

-0.26 -0.73

(a) K and n as defined in Eq 1; L, longitudinal; T, transverse. See Table 1 for remaining symbol definitions.

(b) See Eq 3.

Source: Ref 1

Fig. 1 Typical stress-strain curves for selected metals

Ultimate strength refers to the maximum stress that a material can withstand before failure occurs. The ultimate

strength is related to the materials composition, mechanical working, and heat treatment. The term ultimate

tensile strength is synonymous with tensile strength, which is the accepted ASTM term for the maximum stress

obtainable before fracture of the specimen.

Yield strength is commonly defined as the load at which a given amount of plastic strain has occurred. The

yield strength is related to the materials composition, mechanical working, and heat treatment.

Elastic limit (or proportional limit) is the load at which plastic deformation begins to take place. Removal of the

load allows the material to return to its initial shape. This property of materials is not commonly used in the

design of components.

Modulus of elasticity is the ratio of stress to strain below the elastic limit. The modulus is a measure of material

rigidity or stiffness for loading under tension, compression, or shear. The tensile modulus of elasticity (E), in

principle, is roughly equivalent to the modulus in compressive. The shear modulus (or the modulus of rigidity,

G) is related to the tensile modulus as follows:

(Eq 2)

where μ is Poisson's ratio.

The moduli are usually characteristic for a given materials family such as aluminum, steel, and so on. Table 3

(Ref 2) provides data on the relative stiffness of a number of materials. Tensile moduli range from 45 to 207

GPa (6.5 × 10

to 30 × 10

psi) for common metallic materials.

Table 3 Comparison of the stiffness of selected engineering materials

Material Modulus of

elasticity (E), GPa

Density (ρ),

mg/m

E/ρ × 10

-5

E1/2/ρ × 10

-2

E1/3/ρ

Steel (carbon and low alloy) 207 7.825 26.5 5.8

35.1

Aluminum alloys (average) 71 2.7 26.3 9.9

71.2

Magnesium alloys (average) 40 1.8 22.2 11.1

88.2

Titanium alloys (average) 120 4.5 26.7 7.7

50.9

Epoxy-73% E-glass fibers 55.9 2.17 25.8 10.9

81.8

Epoxy-70% S-glass fibers 62.3 2.11 29.5 11.8

87.2

Epoxy-63% carbon fibers 158.7 1.61 98.6 24.7

156.1

Epoxy-62% aramid fibers 82.8 1.38 60 20.6 146.6

Source: Ref 2

Dynamic Modulus. Modulus can also be determined from resonant vibrations with piezoelectric or

electromagnetic transducers. ASTM standards C 1198 and C 1259 describe test method for determining the

dynamic elastic module of advanced ceramics. These standards also form the basis for two recent additions to

ASTM standards:

• ASTM E 1875-98; Standard Test Method for Dynamic Young's Modulus, Shear Modulus, and Poisson's

Ratio by Sonic Resonance

• ASTM E 1876-98; Standard Test Method for Dynamic Young's Modulus, Shear Modulus, and Poisson's

Ratio by Impulse Excitation

These two standards are almost verbatim versions of C 1198 and C 1259, which are generic and need not be

confined to advanced ceramics, but are applicable to all elastic materials.

In resonant methods, Young's modulus, sheer modulus, and Poison's ratio can all be computed from the

resonant frequencies of prismatic bar, rods, or slabs. Dynamic methods of measuring elastic moduli are related

to adiabatic conditions; whereas, static methods are isothermal. For ceramic materials (Ref 3), the adiabatic

values can be of the order of 0.1% higher than isothermal values (Ref 4).

ASTM C 1198 is a clone of two earlier ASTM standards (C 848 and C 623) that are suitable for ceramic

whitewares, and glass and glass-ceramics, respectively. Rather than using the tables and graphs in the earlier

standards, the newer standard C 1198 uses the original equations for relating the elastic constants to the

resonance frequencies. Although recommended sizes for flat and round specimens are given, the equations are

sufficiently general that a wide size range can be used. The equations include the conventional polynomial

correction factors to reflect the finite specimen thicknesses, but simplified equations are also provided for

instances where the length-to-thickness ratio of the specimens is greater than 20. Specimen flatness and

parallelism are critical; but, with proper care, accuracies and precisions of better than 1% are feasible. C 1198 is

primarily intended to be used with monolithic, or whisker-or particulate-reinforced ceramics. There is some

potential for its use on continuous-fiber reinforced ceramics.

ASTM C 1259 describes a similar but more modern methodology for measuring the same properties as C 1198

except that impulse rather than continuous excitation is used to resonate the specimen. The fundamental

resonant frequency of a rectangular-shaped specimen is measured following mechanical excitation by a singular

elastic strike with an impulse tool. The resulting vibrations are monitored and transformed into electrical

signals. The signals are analyzed and the properties calculated with a knowledge of the mass and dimensions of

the specimen.

JIS Standard R 1602 also uses the resonance frequency method, but goes further by incorporating several

alternate procedures. These include measurements of the static deflection of a beam in bending (with proper

corrections for machine compliance), the strain in a strain-gauged specimen loaded in flexure, or the

longitudinal-wave velocity in an ultrasonically pulsed specimen. The elevated temperature standard JIS R 1605

incorporates the resonance frequency or ultrasonic pulse methods to compute dynamic elastic moduli. Both

Japanese standards prescribe specimen length to thickness ratios of 20 or greater. The same simplified formulas

as given in ASTM C 1198 are used.

Elongation and reduction of area are ductility measurements determined during static mechanical testing and

are related to the plastic deformation that takes place between the elastic limit and the ultimate strength of a

material. These properties are useful when evaluating ductility during deformation such as extrusion, forging,

or drawing.

Poisson's ratio, μ, is the ratio between axial strain to lateral strain during tensile loading. It usually has a value

of approximately 0.3 for most metallic materials. For some materials with anisotropic crystal structures (such as

the hcp structure of titanium α or α-β alloys with a preferred or textured crystal orientation), Poisson's ratio may

depend on orientation.

Design of components for tensile loads normally uses the “fail-safe” concept of design in which a safety factor

is applied to either the yield strength or the ultimate strength of the material. Design using cast materials

typically uses the ultimate strength, whereas design using wrought materials uses the yield strength. Design that

anticipates rapid loading often utilizes the ratio of yield strength to ultimate strength. A material having a ratio

above 0.75 often will fail due to its inability to undergo plastic deformation under load.

Flexural Modulus and Strength. For ceramics and polymer materials, modulus and strength is often evaluated

by flexural testing. In the case of ceramics, bend testing eliminates the gripping problems associated with the

tension testing of ceramics.

Flexural testing by either three-point or four-point loading is the traditional method for evaluating the uniaxial

strength ceramics. The method is applicable for purposes of material development, and sometimes design.

However, for design purposes, tension testing is generally preferred (Ref 5).

Standards for the flexural testing of ceramics include:

• ASTM C 1161-90 Standard Test Method for Flexural Strength of Advanced Ceramics at Ambient

Temperature

• ASTM C 1211-92 Standard Test Method for Flexural Strength of Advanced Ceramics at Elevated

Temperature

• MIL STD 1942 Flexural Strength of Advanced Ceramics at Ambient Temperatures

• JIS R 1601 Testing Method for Flexural Strength (Modulus of Rupture) of High-Performance Ceramics

• JIS R 1604 Elevated Temperature Testing Method for Flexural Strength

• EN 843-1 Monolithic Ceramics, Mechanical Properties at Room Temperature, Part 1: Determination of

Flexural Strength.

The latter standard has been adopted by the European Community and supercedes previous European Standards

(DIN 51-110 Part 1 and AFNOR B41-104). There are many similarities between these standards. The specimen

and fixture sizes are quite comparable and many tolerances and specifications are identical. Nevertheless, there

are some differences that are of concern as discussed in Ref 5. For example, the U.S. and European standards

require the load rollers to be free to rotate to eliminate friction error, but the JIS standard does not.

Although the flexure test is a simple method, significant errors (>5%) can occur from twisting, misalignment,

and frictional constraints (Ref 3). Flexure testing of continuous-fiber, ceramic matrix composites must be

viewed with considerable caution because the failure mode could be tension fracture, shear fracture,

compression failure, or buckling.

Hardness testing is a very common mechanical test applied to materials. Hardness testing is used extensively in

quality control, where data can be collected that relate the mechanical properties of a given material, its

microstructure, and processing methods.

Over the years, many researchers have endeavored to relate hardness values obtained from mechanical testing

to the properties of the material. This has proved to be difficult because the shape of the indenters, loads, and

rate of loading interact with each material in a different manner. For example, an annealed material will work

harden during the test differently than the same material that has received various degrees of cold work.

Materials such as carbon and alloy steels, which are strengthened by different processes (such as annealing,

normalizing, and hardening), have different work-hardening behavior that influences indentation results.

Likewise, cast aluminum alloys have similar hardness values to the wrought alloys yet possess significant

different mechanical properties. Therefore, the correlation of strength and hardness (much like the conversion

of hardness readings for different hardness scales) depends on the material, its condition, and the underlying

strengthening mechanisms.

More information on the factors and variation of strength-hardness correlations are discussed in the article

“Selection and Industrial Applications of Hardness Tests” in this Volume. In fact, Fig. 15(b) in that article

illustrates an example of an inverse correlation of tensile strength and hardness for a line pipe steel. The

explanation of this unexpected result is not clear, but it demonstrates the need for caution and empirically

derived analysis when estimating mechanical strength from hardness.

References cited in this section

1. M.R. Mitchell, Fundamentals of Modern Fatigue Analysis for Design, Fatigue and Fracture, Vol 19,

ASM Handbook, ASM International, 1996, p 231

2. M.M. Farag, Properties Needed for the Design of Static Structures, Materials Selection and Design, Vol

20, ASM Handbook, ASM International, 1997, p 510

3. C.R. Brinkman and G.D. Quinn, Standardization of Mechanical Properties Tests for Advanced

Ceramics, in Mechanical Testing Methodology for Ceramic Design and Reliability, Marcel Dekker,

1998, p 353–386

4. R. Morrell, Handbook of Properties of Technical and Engineering Ceramics, Vol 1, Her Majesty's

Stationary Office, London, 1989

5. G.D. Quinn and R. Morrell, “Design Data for Engineering Ceramics: A Review of the Flexure Test,” J.

Am. Ceram. Soc., Vol 74 (No. 9), 1991, p 2037–2066

Introduction to Mechanical Testing of Components

Properties and Design for Dynamic Loads

Mechanical design is commonly based on static loading of a component. However, there are many components

that see an initial dynamic load followed by static or cyclic loading. Typical examples are explosive fasteners

driven into concrete walls, the torsion spring used in overhead door mechanisms, dies for metal-forming

operations, and aircraft landing gears. Impact tests and fracture toughness tests are the most common tests

performed to demonstrate how materials behave under dynamic loads. These types of tests are performed to use

standard test specimens and often bear no relationship to the complex shapes present in components. The rate of

loading is also kept to standard conditions.

Impact testing of materials provides information on how a material will perform under dynamic loading. The

data obtained from impact testing provide no values that can be used in the designing of components. The data

do provide comparative information between different materials as well as the difference between lots of

materials and/or heat treatment. The data are often plotted as a function of temperature because many materials

exhibit a loss in impact strength as the temperature is lowered. This point is defined as the transition

temperature (Fig. 2).

Fig. 2 Ductile-brittle temperature transition. bcc, body-centered cubic; fcc, face-centered cubic

The most common impact tests are the Charpy and Izod tests, in which the notched specimen is struck by a

hammer. The notch concentrates the stresses so that plastic flow is minimized, and almost all of the energy is

used to fracture the specimen. Other less-common impact tests are the tensile and torsional impact tests, which

measure the performance of materials under these conditions.

The tensile impact test provides comparative information on the differences between various materials and lots

of materials. It also can be used to predict the forming characteristics of materials being fabricated by high-

energy forming methods. The torsional impact test provides information on how tubular cross sections of

various materials will perform under load. The most common application of these data is for shafts that are

rapidly brought up to an operating speed and supplement the torsional fatigue data on these sections. The test is

rarely performed on solid specimens due to the more complex stress state that exists in this geometry.

Fracture toughness testing evaluates the ability of a material to withstand fracture in the presence of cracks.

When fracture toughness is used as design criteria, the designer must be aware that the failure of the component

will occur at nominal stresses below the design stresses for the given material. Cracks, discontinuities, and

microscopic features such as inclusions and other anomalies are often present in components and should be

accounted for in the design process.

The design philosophy for fracture toughness falls into four categories:

• Infinite-life design: This philosophy assumes that the component has no defects that will affect the life

of the component. This philosophy incorporates the traditional design method that uses the fatigue

(endurance) limit of the material.

• Safe-life design: This approach uses a design stress based on the number of cycles at the working stress

that the component must carry to perform its task.

• Fail-safe design: This design philosophy assumes that the structure will continue to support its load

after the failure of a single component of the structure. Fail-safe designs often include the presence of

cracks.

• Damage-tolerant design: This approach was developed by the U.S. Air Force and incorporates the

detection of cracks along with the crack growth rate of the material. Based on life histories, the

remaining life of the component is determined.

Introduction to Mechanical Testing of Components

Properties and Design for Cyclic Loads

In the real world, very few components are subject to static tensile, compression, and bending loads. The

common approach for design of components in fatigue is the design-life approach, where data obtained from

cyclic testing are presented as an S-N curve. The data from S-N testing are often combined in a constant-life

fatigue diagram, which combines the alternating stress conditions with the cycles to failure. One of the

advantages of such a diagram is that the effect of different loading conditions is easily seen in this type of

diagram. Figure 3 (Ref 6) shows a typical constant-life diagram for alloy steel. This type of diagram can be

used to construct S-N diagrams for the expected loading of the component.

Fig. 3 Constant-life diagram for alloy steels. The data in this type of representation can be used to create

an S-N curve for any level of mean stress. Note the presence of safe-life, finite-life lines on this plot. This

plot. This diagram is for average test data for axial loading of polished specimens of AISI 4340 steel

(ultimate tensile strength, UTS, 125 to 180 ksi) and is applicable to other steel (e.g., AISI 2330, 4130, and

8630). Source: Ref 6

External and internal notches significantly reduce the fatigue properties of materials. For example,

precipitation-hardened metals exhibit lower fatigue properties than would be expected from their yield/tensile

properties. Ceramics and glasses contain internal defects, which reduce their expected fatigue strengths. The

operating environment can produce external defects such as corrosion pits or stress corrosion cracks, which can

serve as initiation sites for fatigue to occur.

Fatigue life data are also expressed in terms of a strain-based fatigue, which is divided into an elastic (high-

cycle) component and a plastic (low-cycle) component as follows (Ref 1):

(Eq 3)

where N

is the number of cycles to failure, σ′

is the cyclic true fracture, ε′

is the true fracture strain, and b and

c are constants for a given material. Values for selected steels and aluminum alloys are listed in Tables 1 and 2,

respectively.

Use of published fatigue data and stress concentrations combined with appropriate calculations and rate of

loading provide only an approximation of the useful life of a component. If repeated failures of a component

occur, a statistically designed, factorial test program should perform to validate the design assumptions. Data

obtained from strain gage measurements are useful in the design of the experiment.

Tension-tension (axial) fatigue commonly occurs in press frames, bolted assemblies, and components subjected

to thermal stresses. In the case of a press frame, it would be a zero to maximum tensile loading condition. The

bolted joint normally has a preload applied so that the loading of the bolt is between a mean and maximum

tensile stress. A bridge that undergoes thermal expansion will have both compressive and tensile loading, with

the mean stress being that of the ambient temperature at time of construction. Many materials exhibit a good

correlation of axial fatigue strength with their yield and/or ultimate strengths and typically have a ratio of 0.3 to

0.5 to these properties.

Bending fatigue results in the outer surface being subjected to alternating tensile and compressive stresses in

varying ratios with the limiting strength being in the tensile direction. Common components subjected to

bending fatigue include flapper-type valves and gear teeth. The stresses are given by:

σ = (Mc)/I

(Eq 4)

where M is the bending moment, c is the distance from the center of the section to the outside surface, and I is

the moment of inertia of the section.

Since the maximum stress is at the surface, processes such as shot peening and carburizing that produce

compressive stresses are often used to improve the properties of the material.

Rotating bending fatigue tests have been performed for many years, and the bulk of fatigue data presented in

the literature were produced by the R.R. Moore rotating bending fatigue machine. In this type of loading, a

given point on the outside diameter of the specimens is subjected to alternating tensile or tensile-compressive

stress each time it undergoes a 360° rotation. The effects of various stress concentrations on rotating bending

endurance limits are also readily available. These data are widely used for shafts that are subjected to varying

degrees of misalignment and are the predominate failure modes for these components.

Torsional fatigue data are less commonly reported in the literature. These are the predominate failure modes of

compression springs and shafts that are connected to drive gears. For steels, the ratio between rotating bending

and torsional endurance limits is typically 0.8.

Fatigue crack growth rates are directly related to the material's crystal structure, stress level, rate of loading, and

stress concentrations present in the component. The field of fracture mechanics has provided significant data on

the growth rate of fatigue cracks under axial loading where fracture toughness (K

) has been determined for a

wide variety of materials.

References cited in this section

1. M.R. Mitchell, Fundamentals of Modern Fatigue Analysis for Design, Fatigue and Fracture, Vol 19,

ASM Handbook, ASM International, 1996, p 231

6. D.W. Cameron and D. Hoeppner, Fatigue Properties in Engineering, Fatigue and Fracture, Vol 19,

ASM Handbook, ASM International, 1996, p 19

Introduction to Mechanical Testing of Components

Mechanical Properties and Design for High Temperature

Creep properties of materials are those in which a material continues to elongate under constant load at the

working temperature of a component. Creep damage usually results in fracture, and creep properties of metallic

materials are significant in such diverse applications as a toaster heating element, automobile exhaust system

components, high-temperature steam lines, furnaces and burners, and jet engine turbine components. It is of

major importance for polymers, which exhibit creep at or just above room temperature.

Stress-rupture testing is also used to evaluate the creep resistance of materials. In this test, the sample is

subjected to a constant load, and the time to fracture is measured as it varies with stress and temperature. It is

often used as an acceptance test for high-temperature materials since it can be performed more rapidly than

creep testing can. Creep fatigue results when cyclic loading occurs at elevated temperatures where creep

damage can occur. It is directly related to the crack growth properties of the material, and is discussed in the

article “Creep Crack Growth Testing” in this Volume. In general, materials are classed as being either creep-

ductile materials (iron-base materials fall within this group) or creep-brittle materials (this group includes high-

temperature aluminum alloys, titanium alloys, nickel-base high-temperature alloys, and ceramics).

Creep of Ceramics. Ceramics also exhibit creep behavior. Use of advanced ceramics for elevated temperature

applications may involve the need for constitutive laws in order to predict deformation or strain up to a

specified limit as established by design. Similarly creep-rupture models may also be required. Bending test data

obtained at temperatures within the creep range are not suitable for establishing these laws because of

difficulties in interpretation of specimen behavior (Ref 5). Therefore, to formulate these laws, data must be

generated in both pure tension or compression in accordance with established standards.

ASTM C 1291 is a new standard that covers determination of the elevated-temperature time-dependent

deformation tensile (creep) and stress-rupture properties of monolithic ceramics. Creep time-to-failure is also

included in this test method. This method is only suitable for monolithic ceramics. This test is not suitable for

continuous fiber-reinforced ceramic composites, which do not behave as isotropic, homogeneous materials.

Specimens (dogbone flats or rounds) are subjected to uniform stress in the gage area, where creep deformation

is measured by either optical or mechanical extensometers (Ref 7, 8, and 9). Optical extensometers provide

good stability, while mechanical devices may have advantages in terms of accuracy and ease of use.

References cited in this section

5. G.D. Quinn and R. Morrell, “Design Data for Engineering Ceramics: A Review of the Flexure Test,” J.

Am. Ceram. Soc., Vol 74 (No. 9), 1991, p 2037–2066

7. H. Pih and K.C. Liu, “Laser Diffraction Methods for High Temperature Strain Measurements,” Exp.

Mech., March 1991, p 60–64

8. K.C. Liu and J.L. Ding, “A Mechanical Extensometer for High Temperature Tensile Testing of

Ceramics,” J. Test. Eval., Sept 1993, p 406–413

9. J.Z. Gyekenyesi and P.A. Bartolotta, “An Evaluation of Strain Measuring Devices for Ceramic

Composites,” J. Test. Eval., Vol 20, 1992, p 285–295

Introduction to Mechanical Testing of Components

Applications Factors in Mechanical Performance

Application of materials properties along with the operating stresses calculated from traditional mechanics

yields only a best-case scenario for the performance of a component. Design shape, environmental effects and

surface degradation, the manufacturing method, and the condition of the material all play significant roles in the

design process.

Part Shape. In almost all cases, engineering components and machine elements have to incorporate design

features that introduce changes in their cross section. For example, shafts must have shoulders to take thrust

loads at the bearings and must have keyways or splines to transmit torques to or from pulleys and gears

mounted on them. Under load, such changes cause localized stresses that are higher than those based on the