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Materials and Materials Processing

Purpose of Course  showclose

This self-contained course presents a sampling of the fields of Materials Engineering and Materials Science. This course is intended primarily for engineering students who are not planning to major in either Materials Engineering or Materials Science. We will focus primarily on the concerns of the materials engineer—the person interested in choosing materials to make a finished product. This selection is determined by compromises among material properties, ease of fabrication, and cost. In contrast, the materials scientist is concerned with understanding the relationships between material properties and the internal structure of a material—that is, atomic bonding, arrangements of atoms, grain structure, and other microscopically observable features. We leave most of these associations to advanced courses, which will use more chemistry and physics than needed for this course.

The course is divided into four units:

  • Unit 1: Ways That Materials Can Fail – What Can Go Wrong?
  • Unit 2: Classes of Engineering Materials – What Do We Have?
  • Unit 3: Comparison of Engineering Materials – ­Which Is Best?
  • Unit 4: Processing of Materials – How Can We Shape It?

In Unit 1, we will look at available handbook properties and laboratory test results that characterize a material’s strength or weakness to failure. We will concentrate on mechanical property failures, leaving electrical and other types of breakdown to other courses. Our concerns will be:

  • Static, steady-state applied forces (Elastic Deformation)
  • Ductile materials (Plastic Deformation)
  • Brittle materials (Fast Fracture)
  • Cyclic, vibration forces (Fatigue Failure)
  • High temperature environments (Creep Deformation)
  • Corrosive environments (Oxidation and Wet Corrosion)

In Unit 2, we will identify four major classes of the tens of thousands of available materials: metals, polymers, ceramics, and composite materials. We will examine specific examples from each category.

Unit 3 is a synthesis of the first two units. We will see the consequences of the numerical handbook values defined in Unit 1 in evaluating the materials in Unit 2.

In Unit 4, we will look at how we process our materials to obtain the desired configurations for our products. Your study will include a look at casting, mechanical forming, sintering, and joining. Not all materials can be processed with all procedures.

Course Information  showclose

Welcome to ME203. General information about this course and its requirements can be found below.

Course Designer: Professor Richard J. Greet

Primary Resources: This course comprises a range of different free, online materials. However, the course makes primary use of the following materials: text material specifically written for this course, videos to illustrate and amplify the course material, and computational exercises with worked-out solutions.
                              
Requirements for Completion: In order to complete this course, you will need to work through each unit and all of its assigned materials. You will also need to complete the Final Exam.

Note that you will only receive an official grade on your final exam. However, in order to adequately prepare for this exam, you will need to work through all of the resources in each unit.

In order to pass this course, you will need to earn a 70% or higher on the final exam. Your score on the exam will be tabulated as soon as you complete it. If you do not pass the exam, you may take it again.

Time Commitment: This course should take you a total of approximately 100 hours to complete. Each unit includes a time advisory that lists the amount of time you are expected to spend on each subunit. These should help you plan your time accordingly. It may be useful to take a look at these time advisories, to determine how much time you have over the next few weeks to complete each unit, and then to set goals for yourself. For example, Unit 1 should take 30 hours. Perhaps you can sit down with your calendar and decide to complete subunit 1.1 (a total of 4 hours) on Monday night; subunit 1.2 (a total of 5 hours) on Tuesday and Wednesday nights; etc.

Tips/Suggestions: This course deals with the engineering materials that surround us and that we use every day. Identifying associations in addition to those mentioned in the course will enhance the excitement of learning. Throughout the course, key words that might be typed into search engines to help enhance your knowledge about definitions of terms and concepts will be identified by bold font. A word of caution: most searches will contain references to Wikipedia. Generally, the accuracy of Wikipedia in the sciences is very good, but because anyone can post on a wiki, Wikipedia information should be checked with other references.

As you read, take comprehensive notes. Mark down any important concepts and definitions that stand out to you. These notes will serve as a useful review as you prepare and study for your final exam. 

Learning Outcomes  showclose

Upon successful completion of this course, you will be able to:
  • describe the common mechanisms by which engineering materials fail;
  • associate common descriptive words like strong, tough, and brittle with engineering handbook values;
  • describe the laboratory tests that measure these handbook values;
  • describe the general internal structure of each major class of engineering material: metals, plastics (also known as polymers), and ceramics;
  • compare the strengths and weakness of the major materials classes;
  • identify examples of combining materials from different classes to fabricate composite materials, often with unique properties;
  • select candidate materials for various engineering design scenarios;
  • rank competitive materials using handbook data;
  • identify the principal concerns of common materials processing techniques; and
  • examine advantages and disadvantages of alternative processing techniques when selecting materials.

Course Requirements  showclose

In order to take this course, you must:

√    have access to a computer;

√    have continuous broadband Internet access;

√    have the ability/permission to install plug-ins or software (e.g., Adobe Reader or Flash);

√    have the ability to download and save files and documents to a computer;

√    have the ability to open Microsoft files and documents (.doc, .ppt, .xls, etc.);

√    have competency in the English language;

√    have read the Saylor Student Handbook; and

√    have mathematical competence to at least the level of MA001: Beginning Algebra. It is recommended that you complete the following courses, though these are not prerequisites: MA101: Single-Variable Calculus; PHYS101: Introduction to Mechanics; and CHEM101: General Chemistry I.

Unit Outline show close


Expand All Resources Collapse All Resources
  • Unit 1: Ways That Materials Can Fail – What Can Go Wrong?  

    When a material is subjected to forces, it responds by changing its shape. In the worst case, it breaks apart. Engineers identify two types of shape change: elastic deformation (recoverable) and plastic deformation (permanent). Elastic deformation is when we stretch a rubber band and it snaps back to its original length when we let go. Plastic deformation is the dent in an automobile fender.

    When applied forces are small, we observe only elastic deformation. For brittle materials, that is all we observe. The definition of a brittle material might be: (elastic deformation) → (fracture).

    Other materials are ductile materials. For these materials, increasing the applied forces results in plastic deformation being superimposed onto the initial elastic deformation. With ductile materials: (elastic deformation) → (plastic deformation) → (fracture).

    Engineers measure shape change by defining a property called mechanical strain. Strain is a dimensionless number most often expressed as a percent. (Note: Actually, the engineer does not include the qualifier mechanical, but if we type just strain into a search engine, we will get mostly medical results.) To isolate just the material properties, the engineer expresses forces as mechanical stress,which is force per unit area like with atmospheric pressure.

    When a material suddenly snaps, the situation is referred to as fast fracture. This may occur even when initial force loads appear to be within safe limits. Contributing conditions can be studied by impact testing (particularly at low temperatures), fatigue testing (often simulating vibration), and creep testing (particularly at high temperatures). Also, considered material failure is interaction with the environment­ – corrosion by oxidation and/or wet corrosion.

    Unit 1 Time Advisory   show close
    Unit 1 Learning Outcomes   show close
  • 1.1 Elastic Deformation  

    Please note the following information on elastic deformation:

    • Materials of high elastic modulus are referred to as stiff; materials of low elastic modulus are referred to as flexible.
    • The elastic modulus of metals is relatively insensitive to alloy content.
    • Elastic deformation depends on material property (elastic modulus) and geometry (how thick, for example). Generally, materials are not chosen based on modulus, because deformation can be restrained by changing geometry. We shall see example calculations of this in Unit 3.

  • 1.1.1 Mechanical Stress  
  • 1.1.2 Mechanical Strain  
  • 1.1.3 Elastic Constants  
  • 1.2 Plastic Yielding  

    Please note the following information on plastic yielding:

    • Materials of high yield strength are referred to as strong; materials of low yield strength are referred to as weak.
    • Materials of high percent elongation are referred to as ductile; materials of low percent elongation are referred to as brittle.
    • Yield strength is sensitive to processing; many metals can be processed to be weak during fabrication and subsequently be processed to be strong.
    • Hardness numbers can be calibrated to be a measure of yield strength.

  • 1.2.1 Yield Strength  
  • 1.2.2 Tensile Test  
    • Reading: The Saylor Foundation’s “Tensile Test”

      Link: The Saylor Foundation’s “Tensile Test” (PDF)

      Instructions: Please read this short article, which introduces the tensile test.

    • Reading: Middle East Technical University: Dr. Riza Gürbüz’s “Tension Test”

      Link: Middle East Technical University: Dr. Riza Gürbüz’s “Tension Test” (PDF)

      Instructions: Please click on the link above and download and read the “Tension Test PDF.” Some material in the document is a repeat of the material in this section, while some material expands on the material presented in this sub-subunit. You may skip over the details of performing an experiment, but note especially the diagrams in the Appendix.

      Reading this document should take approximately 30 minutes.

      Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

    • Web Media: YouTube: Learn ChemE’s “Stress-Strain Diagrams”

      Link: YouTube: Learn ChemE’s “Stress-Strain Diagrams” (YouTube)

      Instructions: Please click on the link above and watch this brief video, which presents some of the same information.

      The reference to dislocation motion at the yield stress is a topic we will visit later. The hand-sketched stress-strain curve shows nicely that plastic deformation occursin addition to elastic deformation. Wherever we unload, whether at the yield point or at fracture, we recover the elastic deformation, with the sample following a line parallel to the initial loading line. Note that the curve is not representative of what is seen in the laboratory. For a sample of 20% elongation and an elastic limit of about 0.2%, the totally elastic region would represent only 1/100th of the graph – just about the width of the vertical axis line.

      Watching this video and pausing to take notes should take approximately 15 minutes.

      Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

    • Web Media: YouTube: Laboratory Testing Inc.’s “Tensile Test Stainless Steel Specimen”

      Link: YouTube: Laboratory Testing Inc.’s “Tensile Test Stainless Steel Specimen” (YouTube)

      Instructions: Please click on the link above and watch this brief video to see a tensile sample necking before fracture.

      At the start of the video, the speaker mentions having a 500-diameter tensile specimen. He means that the sample has a diameter of 0.500 inches. Actually, the standard diameter is 0.505 inches, as this diameter computes a cross-sectional area of 0.200 square inches, and makes the engineering stress in psi (pounds per square inch) numerically five times the force in pounds. If you can resolve the graph being plotted by the test machine, you will note that this sample exhibits a sharp change in slope (yield point) as plastic deformation begins.

      Watching this video (several times as needed) and pausing to take notes should take approximately 15 minutes.

      Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

  • 1.2.3 Hardness  
    • Reading: The Saylor Foundation’s “Hardness”

      Link: The Saylor Foundation’s “Hardness” (PDF)

      Instructions: Please read this short article, which introduces hardness.

    • Reading: Gordon England’s “Hardness Testing”

      Link: Gordon England’s “Hardness Testing” (HTML)

      Instructions: This is a nice reference page that provides the mathematical definitions of the scales mentioned in this section, plus identification of some other hardness measurements. Read the definition of hardness, explore some of the links on different types of hardness test methods, and explore some of the links on conversion charts and tables. It may be helpful to use this website as a reference throughout the course.

      Reading this webpage should take approximately 1 hour.

      Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

  • 1.3 Fast Fracture  

    Please note the following information on fast fracture:

    • A critical combination of stress and crack length can result in cracks becoming unstable, propagating with the speed of sound to snap the product to failure. This occurs even though the nominal level of stress is less than the yield stress.
    • Micro cracks may be a product of processing, especially in large welded structures.
    • Micro cracks may also nucleate during service, especially during repetitive loading situations or over extended periods of time.
    • Materials resistant to fast fracture are referred to as tough.
    • Fast fracture is particularly a concern at low temperatures. Materials that are ductile at room temperature may become brittle at cold temperatures.

  • 1.3.1 Energy Criterion  

    A sample with an interior crack has a higher internal energy than a sample without a crack, because of the surface energy of the crack surfaces. If this were the only concern, then cracks should be self-healing to lower the total internal energy. In practice, cracks in unstressed materials do not heal, but remain at a stable length. However, if a crack grows into material that is elastically stressed, the crack lowers the stored elastic energy in the surrounding material. This favors crack growth. Thus, we have a competition of two effects. The result of this competition can have two alternative interpretations:

    • At a given stress (stored elastic energy level), there is a critical crack length. Shorter cracks are stable; longer cracks propagate to fracture.
    • For a given crack length, there is a critical stress. At lower stresses, the crack is stable; at higher stresses, the crack propagates to fracture.

  • 1.3.2 Stress Intensity Factor  
  • 1.3.3 Impact Test  
  • 1.4 Fatigue Failure  

    Please note the following information on fatigue failure:

    • Fatigue failure is fast fracture occurring after many cycles of repetitive stress, often resulting from vibrations during service, such as with an airplane wing.
    • Tensile stresses nucleate, grow, and eventually cause fast fracture of micro cracks.
    • Fatigue failure measurements show considerable scatter.

  • 1.4.1 Fatigue Failure Mechanism  
  • 1.4.2 Rotating Beam Fatigue Test and S-N Charts  

    A standard documentation of high cycle fatigue failure is the rotating beam fatigue test. A rotating sample is loaded with a torque that causes a surface element to undergo alternating tension and compression as the sample rotates. If a crack has nucleated, the tension portion of the loading causes the crack to grow. The results of many such tests to failure are summarized on a S-N diagram (Stress versus Cycles to Failure). This is a statistical summary. Each test defines a single point. There is typically considerable scatter in the results.

    • Web Media: YouTube: I.Get.It’s “Fatigue Analysis Overview”

      Link: YouTube: I.Get.It’s “Fatigue Analysis Overview” (YouTube)

      Instructions: Watch this video, which defines the S-N diagram. The video illustrates computer modeling of the fatigue test. COSMOSWorks is commercially available, finite element software. In the video, the test is shown as a uniaxial tensile test, though rotating bending beam tests are more common.

      The load cases defined at the end of the video are not considered in this course. Probably the most important observation is that many steels show an endurance limit. If stresses are held below this value, then failure by fatigue will not occur. Conversely, aluminum and many other non-ferrous metals do not show this limit. No matter how low the stresses, sooner or later the part will fail. This is why we must regularly inspect aluminum aircraft frames for fatigue cracks.

      Watching this video and pausing to take notes should take approximately 15 minutes.

      Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

      The Saylor Foundation does not yet have materials for this portion of the course. If you are interested in contributing your content to fill this gap or aware of a resource that could be used here, please submit it here.

      Submit Materials

  • 1.5 Creep Deformation  

    Please note the following information on creep deformation:

    • Creep is plastic deformation that continues to occur over time.
    • Creep deformation is very slow. Strain rates of 1% in 1000 hours, or even 1% over 10 years, are typical.
    • For most materials, creep does not happen at room temperature, only at elevated temperatures.
    • What constitutes an elevated temperature is determined by a material’s melting or softening temperature.

  • 1.5.1 Conditions for Creep  
  • 1.5.2 Measurement and Prediction of Creep  
  • 1.6 Corrosion  

    Please note the following information on corrosion:

    • Corrosion is primarily a concern with metals. Plastics and ceramics are essentially inert in our common atmosphere.
    • Virtually all metals oxidize. However, some oxides are protective, while others are not. Our concern, then, is the nature of the oxide layer that forms.
    • Wet corrosion, also known as electrochemical attack, requires two dissimilar materials. These may be two different chemistries, but many other common situations can establish differences.

  • 1.6.1 Oxidation  
  • 1.6.2 Wet Corrosion  
  • 1.7 Computational Exercises  
  • Unit 2: Classes of Engineering Materials – What Do We Have?  

    The scientist distinguishes materials by the types of bonding between the atomic particles. This in turn is a study of what the valence electrons of the atoms are doing.

    With metallic bonding, the valence electrons disassociate from their parent atoms. They form a cloud that permeates the sample, leaving behind roughly spherical positive ion cores. This electron cloud contributes to both the high electrical and the high thermal conductivity of metals. The spherical ions pack densely into symmetrical crystal lattices. Close-packed planes of ions can slide (shear) over each other for ductile, plastic deformation. The details of this sliding involve defects known as dislocations.

    The defining link in polymers is the covalent bond, also known simply as the chemical bond. This is the bond that defines molecules such as water, carbon dioxide, and ammonia. Covalent bonds require specific angles, resulting in lower density materials. Often, rotation can occur around a covalent bond, leading to rubber-like elasticity. Some polymers, called thermoplastic plastics, consist of long chains, somewhat analogous to a bowl of cooked spaghetti. Other plastics, called thermosetting plastics, are a 3D network of strong covalent bonds.

    Many ceramic materials are again made up of roughly spherical ions, but of differing sizes. Here, a valence electron has escaped from one type of atom and been captured by a different type of atom, resulting in ionic bonding. The smaller positive ions and larger negative ions again pack into symmetrical crystal lattices. Any shearing of planes would bring similar charges into proximity, a condition of strong repulsive force, but this doesn’t happen. Ceramics are brittle. Concrete is considered a ceramic. Other common ceramics include oxides, nitrides, and carbides, which have covalent bonds.

    As the name suggests, composite materials are combinations of the above. Common engineering composites are GFRPs (graphite fiber reinforced polymers) and CFRPs (carbon fiber reinforced polymers). Cermets are combinations of ceramics and metals. A naturally occurring composite material is wood.

    Unit 2 Time Advisory   show close
    Unit 2 Learning Outcomes   show close
  • 2.1 Metals  

    Advantages

    • Most metals are strong, easy to shape, and relatively inexpensive.
    • Metals can be alloyed to be serviceable at extremes of low and high temperatures.
    • Many metals can be alloyed to be heat treatable – ductile in one state and strong in another.
    • Many metals are excellent conductors of both heat and electricity.
    Limitations
    • Metals are relatively heavy.
    • Many metals chemically react with gases and liquids.
    Each class of material has many, often hundreds, of entries. From the metals, we will select four to follow through our comparisons in Unit 3. Two are familiar – steels and aluminum alloys. Two are a little more exotic – magnesium alloys and titanium alloys. We will also look at some other metals in a less comprehensive way.

  • 2.1.1 Steels  
  • 2.1.2 Aluminum and Its Alloys  
  • 2.1.3 Some Other Metals  
  • 2.2 Polymers  

    Advantages

    • Polymers are light in weight.
    • Most polymers are chemically inert.
    • Polymers can be colored throughout, not just surface coated.
    • Elastomers and foamed polymers have unique properties.
    Limitations
    • Most polymers are essentially room-temperature materials, breaking down at either low or high temperatures.
    • Many polymers are soft and scratch easily.
    From the class of polymers, we will select six engineering plastics to follow through our comparisons in Unit 3. Each has a wide variety of applications. We will identify a few uses to establish familiarity.

  • 2.2.1 Engineering Polymers (Plastics)  
  • 2.2.2 Elastomers  

    Elastomer is the scientific name for the familiar rubber-like polymers. These include natural rubber, silicone rubber, and hard and soft butyl rubbers. Whereas the elastic limit of metals and ceramics is about 0.1% strain, rubbery materials can be elastically deformed several hundred percent. Elastomers have an available deformation mechanism that the other materials do not. Like thermoplastics, elastomers are comprised of long molecular chains. In elastomers, these chains tend to be curled up like a ball of yarn in the unstressed condition. Application of a force tends to uncurl the molecular chains, but this is an elastic, reversible deformation.

  • 2.2.3 Foamed Polymers  

    Foamed polymers, like Styrofoam® coffee cups and polyurethane building insulation, consist mainly of closed cells of trapped air. This makes them lightweight and mechanically weak, but also gives them unique properties. It is the trapped dead air spaces that provide thermal insulation, not the polymers themselves. Foamed polymers are useful as packing materials, as they can absorb energy by the crushing of cells, rather than by deformation of a solid material.

  • 2.3 Ceramics  

    Advantages

    • Ceramics are very hard, good for saw blades and drill bits.
    • Ceramics are stable to very high temperatures.
    • Ceramics are inert to corrosion.
    Limitations
    • Ceramics are brittle.
    • Ceramics can require special processing to form.

  • 2.3.1 Engineering Ceramics  
  • 2.3.2 Porous Ceramics  

    These materials are loosely defined and frequently contain several chemical constituents. They become solid ceramics by firing (as with brick, pottery, porcelain) or by chemical reaction, often involving water (as with mortar and concrete).

  • 2.3.3 Glasses  
  • 2.4 Composite Materials  

    Advantages

    • Composites can utilize the best of different materials groups.
    • The internal structure of composites may sometimes be controlled in unique ways – to obtain highly directional properties, for example.
    Limitations
    • Special processing can lead to expensive products.
    • Compatibility of using different materials can cause special problems. Will they successfully bond together, for example?

  • 2.4.1 Advantages of Composite Materials  

    A composite seeks to take advantage of the strengths of two different materials by bonding them together. A familiar example is reinforced concrete. A steel rod is strong in tension, but will buckle under compression. Concrete, like most brittle materials, is about ten times stronger in compression than in tension. By embedding steel reinforcing bars (rebar) within the concrete, we obtain a product that has better combined tensile and compressive strengths than either material alone.

    Another familiar composite is steel-belted automobile tires. We obtain the desired friction with the rubber, together with the stiffening of steel for increased fuel efficiency.

  • 2.4.2 Engineering Composites  

    We will look at three types of engineering composites in our comparisons in Unit 3: glass fiber reinforced polymers (GFRP), more commonly known as fiberglass; carbon fiber reinforced polymers (CFRP), found in sports products; and ceramic/metal combinations. The polymers are generally epoxy resins, making GFRP and CFRP lighter than most metals.

    In addition to combining physical properties, fiber composites can be layered with fibers in alternative layers and orientated in different directions to give desired spatial distribution of strength.

  • 2.4.3 Wood: Nature’s Composite Material  

    Similar to aligned polymer molecules, common woods such as pine, oak, maple, and others have a grain structure. Properties measured parallel to the grain are generally different from properties measured perpendicular to the grain.

  • Unit 3: Comparison of Engineering Materials – Which Is Best?  

    This unit draws from the previous two units. How do we select a material to produce a particular part? We need to avoid the possible failures described in Unit 1 by selecting the best material from the classes listed in Unit 2. Most often, there will be several competing candidates. Part of the evaluation will also include consideration of how the materials can be shaped, which we will investigate in Unit 4.

    Unit 3 Time Advisory   show close
    Unit 3 Learning Outcomes   show close
  • 3.1 Assessing Engineering Environments  
  • 3.2 Density  
  • 3.3 Elastic Stiffness  
  • 3.3.1 Comparison of Materials  
  • 3.3.2 Commentary  
  • 3.3.3 An Example of Materials Selection Based on Elastic Deformation  
    • Web Media: YouTube: Learn ChemE’s “Elastic Properties of Metals”

      Link: YouTube: Learn ChemE’s “Elastic Properties of Metals” (YouTube)

      Instructions: Please click on the link above, and view this brief video. The video presents an application of using handbook data and calculations to select a material for strength and stiffness. While identified as elastic design, yield stress is needed to establish an upper limit for elastic deformation.

      Note: At one point the narrator misrepresents the units of a calculation. When calculating the applied stress, the narrator speaks the units as though they were written N•m and then writes them N/m. Neither is correct. The units for stress are N/m2 or Pa (newtons per meters squared or pascals).

      Watching this video and pausing to take notes should take approximately 15 minutes.

      Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

  • 3.3.4 An Example of Shape Consideration for Elastic Deformation  
  • 3.4 Plastic Deformation Strength  
  • 3.4.1 Comparison of Materials  
  • 3.4.2 Commentary  
  • 3.4.3 An Example of Using Yield Stress for Materials Selection  
  • 3.5 Fast Fracture Toughness  
  • 3.6 Fatigue Failure Resistance  
  • 3.6.1 Geometry  

    Geometry is very important when fatigue loading is a concern. While the overall nominal stress in a part subject to fatigue loading may be kept within calculated safe limits, the local stress at geometric transitions can be much higher. This promotes the nucleation of cracks at these locations, such as at sharp corners. For simple geometries, charts, tables, and equations are available to give values of stress concentration factors. These are multiplying factors between nominal and higher actual stresses. When geometries and loadings are complicated, computer modeling is used. The conclusion is that we should minimize sharp angles with rounded corners to forestall nucleation of fatigue cracks.

  • 3.6.2 Surface Treatments  

    Fatigue failure is sensitive to surface finish. A smooth, polished surface is more resistant than a rough surface. Surface scratches and irregularities can be nucleation sites for fatigue cracks. Further, since cracks grow during the tension portion of fatigue, any treatment that imparts residual compressive stresses into the surface will lengthen fatigue life. A fairly simple procedure to treat metals is shot peening. Parts are tumbled in a bath of hardened metal, ceramic, or glass spheres with sufficient force to cause compressive plastic deformation of the surface.

  • 3.7 Creep Failure Resistance  
  • 3.8 Corrosion Resistance  
  • 3.9 Computational Exercises  
  • Unit 4: Processing of Materials – How Can We Shape It?  

    A material may have the properties we wish, but we still have to shape it for it to be useful as a part. We will consider casting, mechanical forming, sintering, welding, and brazing. These processing techniques will be generally familiar, but we will take a closer look at advantages and disadvantages, and at some specific considerations.

    Unit 4 Time Advisory   show close
    Unit 4 Learning Outcomes   show close
  • 4.1 Casting  

    Advantages

    • Complex shapes can be formed in a single step.
    • Chemically reacting components, such as thermosetting resins and concrete, can be cast.
    Limitations
    • Preparing molds may be time-consuming and expensive.
    • Not all materials can be cast. Some deteriorate at elevated temperatures before they melt.
    • The solidification process imparts a grain structure to the interior of the casting that may not be desirable.

  • 4.2 Mechanical Forming  

    Advantages

    • Cold forming strengthens as well as shapes metals.
    • Long shapes, such as rods and tubes, can be made by extrusion.
    • Hot forming allows almost unlimited change in shape without change in properties.
    Limitations
    • Cold forming increases the brittleness of a metal.
    • Like casting, cold forming imparts internal structure to metals.
    • Brittle materials cannot be mechanically shaped without fracture.

    • Reading: The Saylor Foundation’s “Mechanical Forming”

      Link: The Saylor Foundation’s “Mechanical Forming” (PDF)

      Instructions: Please read this short article, which discusses cold working, annealing, and hot working.

    • Web Media: YouTube: Learn ChemE’s “Dislocations and Plastic Deformation”

      Link: YouTube: Learn ChemE’s “Dislocations and Plastic Deformation” (YouTube)

      Instructions: Please click on the link above, and watch this brief video. This is a presentation of how a plane can be shifted by dislocation movement. The dislocation is into the plane of the drawing, so that we are looking at the end of a line. A different definition of dislocation density is mentioned than that given in the next section. The two definitions are equivalent.

      Watching this video and pausing to take notes should take approximately 15 minutes.

      Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

    • Web Media: YouTube: GSEG Media: George Goehl’s “Copper Annealing”

      Link: YouTube: GSEG Media: George Goehl’s “Copper Annealing” (YouTube)

      Instructions: Please click on the link above and watch this video, which illustrates the annealing of copper. We have to take the narrator’s word that the copper strip is either stiff or soft, but this video emphasizes the purpose of annealing.

      Note: The narrator’s description of work hardening is incorrect. There are no molecules of copper coming closer together; rather, work hardening is caused by the increased density and subsequent entanglement of dislocations discussed in the previous section.

      Watching this video and pausing to take notes should take approximately 15 minutes.

      Terms of Use: Please respect the copyright terms of use displayed on the webpage above.

  • 4.3 Sintering  

    Advantages

    • High-melting and brittle materials often can be formed no other way.
    • Special properties may be achieved by impregnating the porous sintered product with oil, for example.
    Limitations
    • Specialized equipment involving high temperature and atmosphere control are often necessary.
    • The variable density and variation in other mechanical properties of sintered materials may be of concern.

  • 4.4 Joining  

    Advantages

    • Welding and brazing are often economical alternatives to machining or casting.
    • In the field, repair by welding or brazing can often prevent replacement of original parts.
    Limitations
    • Welding is a sequence of alloying, casting, and heat treatment. This complex event has many possibilities for less than desired results.
    • Not all materials can be joined by melting them together.

  • 4.4.1 Welding  
  • 4.4.2 Soldering and Brazing  
  • Final Exam  

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