Technology & Engineering
Toughness
Toughness refers to the ability of a material to absorb energy and deform plastically without fracturing. It is a crucial property in engineering and technology, especially in the design of structures and materials that are subjected to impact or sudden loads. Toughness is often evaluated through tests such as Charpy or Izod impact tests, providing valuable information for material selection and design considerations.
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8 Key excerpts on "Toughness"
eBook - PDF- Arun Shukla(Author)
- 2004(Publication Date)
- CRC Press(Publisher)
Test and Analysis of Fracture Toughness 115 TESTING OF FRACTURE Toughness Traditional design involves simplified models based on the theory of elasticity and the conventional mechanical properties of the materials. Fracture mechanics, as a recent newcomer in the engineering field, offers new approaches to fail-safe design with the objective of reducing the level of conservatism by providing a theoretical stress analysis of the cracked body. This process introduces the flaw size and geometry as additional design parameters, and it requires a good deal of knowledge of relatively new material properties such as fracture Toughness applicable to various modes of cracking and environmental conditions. This sec-tion outlines briefly some of the practical aspects of experimental methodology that may be of interest to design engineers and other practitioners in their search for fracture-resistant materials. One of the overriding interests in this area is con-cerned with the metallic materials, including carbon and low-alloy steels, high-strength steels, and nonferrous products. “Fracture Toughness” and “fracture res-istivity” terminology is sometimes used in the literature dealing with the mech-anical and metallurgical aspects of microfracture modes. [10] It is good to keep in mind various definitions and symbols used during the earlier formative years when considering newer concepts and future developments in experimental methodology. Fracture testing methods have developed during the past 50 years out of necessity. There were very real concerns about structural failures in some of the Liberty ships, followed by the needs of the U.S. military programs in the field of missiles and rockets. Particularly annoying and costly were brittle frac-tures of high-strength materials in rocket motor cases, where conventional design methodology was inadequate to cope with the technical setbacks.
- Donald Askeland, Wendelin Wright(Authors)
- 2018(Publication Date)
- Cengage Learning EMEA(Publisher)
For example, an optical fiber must have a certain level of strength to withstand the stresses encountered in its application. A biocompatible titanium alloy used for a bone implant must have enough strength and Toughness to survive in the human body for many years without failure. A scratch-resistant coating on optical lenses must resist mechanical abra-sion. An aluminum alloy or a glass-ceramic substrate used as a base for building magnetic hard drives must have sufficient mechanical strength so that it will not break or crack during operation that requires rotation at high speeds. Similarly, electronic packages used to house semiconductor chips and the thin-film structures created on the semiconductor chip must be able to withstand stresses encountered in various applications, as well as those encountered during the heating and cooling of electronic devices. The mechanical robustness of small devices fabricated using nanotechnology is also important. Float glass used in automotive and building applications must have sufficient strength and shat-ter resistance. Many components designed from plastics, metals, and ceramics must not only have adequate Toughness and strength at room temperature but also at relatively high and low temperatures. Copyright 2019 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 183 6-2 Terminology for Mechanical Properties For load-bearing applications, engineered materials are selected by matching their mechanical properties to the design specifications and service conditions required of the component.
- Donald Askeland, Wendelin Wright, Donald Askeland(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
For example, an optical fiber must have a certain level of strength to withstand the stresses encountered in its application. A biocompatible titanium alloy used for a bone implant must have enough strength and Toughness to survive in the human body for many years without failure. A scratch-resistant coating on optical lenses must resist mechanical abra- sion. An aluminum alloy or a glass-ceramic substrate used as a base for building magnetic hard drives must have sufficient mechanical strength so that it will not break or crack during operation that requires rotation at high speeds. Similarly, electronic packages used to house semiconductor chips and the thin-film structures created on the semiconductor chip must be able to withstand stresses encountered in various applications, as well as those encountered during the heating and cooling of electronic devices. The mechanical robustness of small devices fabricated using nanotechnology is also important. Float glass used in automotive and building applications must have sufficient strength and shat- ter resistance. Many components designed from plastics, metals, and ceramics must not only have adequate Toughness and strength at room temperature but also at relatively high and low temperatures. Copyright 2022 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 183 6-2 Terminology for Mechanical Properties For load-bearing applications, engineered materials are selected by matching their mechanical properties to the design specifications and service conditions required of the component.
eBook - PDF- T.H.G. Megson(Author)
- 2005(Publication Date)
- Butterworth-Heinemann(Publisher)
C h a p t e r 8 / Properties of Engineering Materials It is now clear from the discussion in Chapter 7 that the structural designer requires a knowledge of the behaviour of materials under different types of load before he/she can be reasonably sure of designing a safe and, at the same time, economic structure. One of the most important properties of a material is its strength, by which we mean the value of stress at which it fractures. Equally important in many instances, particularly in elastic design, is the stress at which yielding begins. In addition, the designer must have a knowledge of the stiffness of a material so that he/she can prevent excessive deflections occurring that could cause damage to adjacent structural members. Other factors that must be taken into consideration in design include the character of the different loads. For example, it is common experience that a material, such as cast iron fractures readily under a sharp blow whereas mild steel merely bends. In Chapter 1 we reviewed the materials that are in common use in structural engineering; we shall now examine their properties in detail. 8.1 C LASSIFICATION OF E NGINEERING M ATERIALS Engineering materials may be grouped into two distinct categories, ductile materials and brittle materials, which exhibit very different properties under load. We shall define the properties of ductility and brittleness and also some additional properties which may depend upon the applied load or which are basic characteristics of the material. DUCTILITY A material is said to be ductile if it is capable of withstanding large strains under load before fracture occurs. These large strains are accompanied by a visible change in cross-sectional dimensions and therefore give warning of impending failure. Materials in this category include mild steel, aluminium and some of its alloys, copper and polymers. 188
eBook - PDF- John Tien(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
Chapter VII FRACTURE Toughness Victor F. Zackay Earl R. Parker M A T E R I A L S S C I E N C E A N D E N G I N E E R I N G D E P A R T M E N T C O L L E G E O F E N G I N E E R I N G , U N I V E R S I T Y O F C A L I F O R N I A B E R K E L E Y , C A L I F O R N I A I. I N T R O D U C T I O N Each chapter of this book deals with alloy design to improve a partic-ular alloy property, such as strength, ductility, or resistance to creep, fatigue, or corrosion. In a large majority of the cases studied, each de-sign is developed to avoid the ultimate material failure, i.e., fracture. Therefore, it is prudent for the alloy designer, concerned with any par-ticular alloy property discussed in this book, to pay particular attention to the importance of material resistance to fracture, i.e., fracture Toughness. In fact, the most important mechanical property required of a struc-tural material is often resistance to sudden or catastrophic fracture. For this reason, metals are usually the materials of choice where such failure would result in loss of life or property. However, the resistance of metals to catastrophic failure is not an intrinsic and fixed quantity. On the con-trary, it changes with the amount and type of stress, the temperature, the strain rate, and environmental variables, i.e., macroscopic factors, as 213 214 Victor F. Zackay and Earl R. Parker well as with alloy composition and structure, i.e., microscopic factors. Consideration of only one set of these factors in either the design of an engineering structure or, alternatively, in the design of an alloy is in-consistent in principle and ineffective in practice. This chapter describes some of the progress made in both the macro-scopic and microscopic approaches to the problem of designing alloys with superior fracture Toughness.
Available until 4 Dec |Learn moreManufacturing Technology
Materials, Processes, and Equipment
- Helmi A. Youssef, Hassan A. El-Hofy, Mahmoud H. Ahmed(Authors)
- 2011(Publication Date)
- CRC Press(Publisher)
. When.materials.fail.with.little.or.no.ductility,.they.are.said.to.be.brittle . . Brittleness ,.therefore,.is.the. opposite.of.ductility.and.should.not.be.confused.with.a.lack.of.strength . .A.brittle.material.is.simply. one.that.lacks.significant.ductility . .Brittle.materials.are.generally.considered.to.be.those.having.a. fracture.strain.of.less.than.5% . Elastic Plastic P 0.002 0 Strain Stress σ y FIGURE 2.2 Stress–strain.curve.of.a.material.that.does.not.have.a.well-defined.yield.point,.showing.the. offset.method.for.determining.the.yield.stress . Properties of Engineering Materials 21 2.3.3 T OUGHNESS This.is.a.measure.of.the.energy.required.to.break.a.material,.whereas.strength.is.a.measure.of.the. stress.required.to.produce.fracture . .This.contrast.is.especially.important.in.view.of.the.fact.that. Toughness.is.often.inaccurately.called.“impact.strength .” .The.modulus.of.Toughness.is.the.energy. per.unit.volume.expressed.in.J/m³;.it.is.the.area.under.the.stress–strain.curve . .A.ductile.material. with.the.same.strength.as.a.nonductile.material.will.require.much.more.energy.for.breaking.and. thus.will.be.tougher . .Figure.2 .3 .demonstrates.the.stress–strain.curves.for.brittle.and.tough.material. types. .Even.though.the.brittle.material.has.higher.yield.tensile.strengths,.it.has.a.lower.Toughness. than.the.ductile.one.due.to.the.lack.of.ductility . .Standardized.Charpy.or.Izod.tests.are.two.of.several. procedures.used.to.measure.Toughness . .They.differ.in.the.shape.of.the.test.specimen.and.method.of. applying.the.energy.(Figure.2 .4). 2.3.4 H ARDNESS Another.important.mechanical.property.to.consider.is. hardness ,.which.is.a.measure.of.material. resistance.to.localized.plastic.deformation . .Therefore,.both.tensile.strength.and.hardness.are.indi-cators.of.a.metal’s.resistance.to.plastic.deformation . .Consequently,.they.are.roughly.proportional,. as.shown.in.Figure.2 .5, .for.tensile.strength.(TS).as.a.function.of.the.Brinell.hardness.number.
eBook - PDFThermoplastic Aromatic Polymer Composites
A Study of the Structure, Processing and Properties of Carbon Fibre Reinforced Polyetheretherketone and Related Materials
- Frederic Neil Cogswell(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
8 Durability No single property of linear chain thermoplastic composite materials has elicited more excitement in both academic and industrial circles than their Toughness in comparison with conventional crosslinked thermosetting materials. The pragmatic concept of Toughness is expressed in the science of fracture mechanics. Usually structures are designed to carry loads that are well below the ultimate strength of the composite materials. Under such circumstances it is the adventitious impact of foreign bodies that is most likely to cause failure in the composite. Such failure may be complete breakage of the fibres. More commonly it is microcracking of the matrix phase or delamination between the individual plies. Thermoplastic composites have the ability to absorb energy by dissipative mechanisms within the matrix phase, thereby minimizing such damage. Their high Toughness also reduces the propagation of any delamination during normal service, and this is of particular importance when the structure is loaded in compression. During their lifetime most structures are subject to intermittent rather than steady loading patterns: in particular the load may vary from tension to compression. It is therefore necessary also to consider the fatigue performance. Finally, materials may be subjected to abrasive loads so that, for a full appreciation of durability, we must also consider the friction and wear resistance of the materials. 8.1 Fracture mechanics The science of fracture mechanics was originally formulated to explain the durability of brittle monolithic materials such as glass. Surprisingly such theories can also be applied successfully to composite materials with complex morph-ology 1 ' 2 . In the case of composite materials their anisotropic nature requires consideration of the fracture mechanics both in terms of the mode of deformation (Figure 8.1) and in respect of the orientation of the fibres.
eBook - PDF- Mikell P. Groover(Author)
- 2012(Publication Date)
- Wiley(Publisher)
Material properties can be divided into two categories: mechanical and physical. The mechanical properties of a material determine its behavior when subjected to mechani- cal stresses. These properties include stiffness, ductility, hardness, and various measures of strength. Mechanical properties are important in design because the function and performance of a product depend on its capacity to resist deformation under the stresses encountered in service. In design, the usual objective is for the product and its components to withstand these stresses without significant change in geometry. This capability depends on properties such as elastic modulus and yield strength. In manufacturing, the objective is just the opposite. Here, we want to apply stresses that exceed the yield strength of the material to alter its shape. Mechanical processes such as forming and machin- ing succeed by developing forces that exceed the material’s resistance to deformation. Thus, we have the following dilemma: Mechanical properties that are desirable to the designer, such as high strength, usually make the manufac- ture of the product more difficult. Physical properties define the behavior of materials in response to physical forces other than mechanical. The properties include volumetric and thermal properties as well as melting characteristics. Physical properties are important in manufacturing because they often influence the performance of the process. Melting characteristics are important in metal casting operations. Metals with higher melting temperatures require more heat input before pouring the molten metal into the mold. In machin- ing, thermal properties of the work material determine the cutting temperature, which affects how long the tool can be used before it fails. 49 In this chapter, we discuss the properties of engineering materials that are most relevant to the manufacturing processes covered in this book.
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