Fracture Toughness & Fatigue & Eng'g Materials, Corrosion Prevention PDF

POGIAKO1234 JHAY LAMBERT MERCADO MARK BILLY BERJA ARTH JESTER RUIZ JAMES ANDREW VILLABERT GROUP 4 Fracture Toughness & Fatigue & Eng'g Materials, Corrosion Prevention  Play + What is Fracture Toughness? Fracture toughness describes a material's resistance to brittle fracture when a cr...

POGIAKO1234 JHAY LAMBERT MERCADO MARK BILLY BERJA ARTH JESTER RUIZ JAMES ANDREW VILLABERT GROUP 4 Fracture Toughness & Fatigue & Eng'g Materials, Corrosion Prevention  Play + What is Fracture Toughness? Fracture toughness describes a material's resistance to brittle fracture when a crack is present. It is related to its ability to deform plastically instead of further increasing the local stress and energy level. Play + Metals hold the highest values of fracture toughness. Cracks cannot easily propagate in tough materials, making metals highly resistant to cracking under stress and gives their stress-strain curve a large zone of plastic flow.  Play + TOUGHNESS VS. FRACTURE TOUGHNESS Toughness is a materials Fracture Toughness it ability to absorb energy measures a materials without fracturing. resistance to fracture when a crack or flaw is Toughness = Strength and present. Ductility 1. Tensile test 2. Impact test  Play + Fracture Toughness Tests A test sample is fatigue loaded to extend the machined notch by a prescribed amount. A clip gage extensometer is placed at the mouth of crack to monitor displacement. If a lower toughness level is achieved with a thicker sample, then the value obtained initially is not valid.  Play + How to Calculate and Solve for Fracture Toughness Play + Play + Type of Specimens for Fracture Toughness Tests Clip Gage Extensometer  Play + What is FATIGUE? Fatigue is a failure mechanism that involves the cracking of materials and structural components due to cyclic (or fluctuating) stress.  TYPES OF FATIGUE High-Cycle Low-Cycle Thermal Fatigue Fatigue Fatigue Contrarily, Low-Cycle This is a specific type of This occurs when Fatigue transpires when fatigue caused by cyclic materials are materials are subjected thermal loads, usually subjected to stresses to higher stresses, as a result of fluctuating much lower than typically exceeding the temperatures. This yield strength over a fluctuation causes their yield strength, smaller number of materials to expand and over a high number cycles. This can cause contract, leading to of cycles. structural failure within stress build-up and thousands or even eventual crack hundreds of cycles. propagation.  Fatigue analysis There are two primary things in understanding fatigue: 1. Initiate a crack Fatigue crack initiation is normally associated with the endurance limit of a material and the stress concentration. 2. Propagate a crack once it is formed. Fatigue crack propagation is associated with the fracture toughness and crack growth characteristics of a material.  The stress field near a fatigue crack tip can be divided into three types: (a) Load applied in y (b) Load applied in x (c) Load applied in z direction Opening direction Sliding direction Tearing (or Mode Mode anti- plane) Mode WHAT IS IMPACT TESTING? Impact tests measure the ability of a material to resist deformation in response to a sudden load. These tests are normally conducted according to test methods and standards published by ASTM International. Four commonly used types of impact tests include: Charpy, Izod, drop-weight, and dynamic tear tests. An impact test is a technique used to determine a material's ability to resist deformation when subjected to a sudden shock or impulse load. There are several different types of impact tests, but all entail striking a prepared test specimen with a weight. Different materials testing standards, such as ASTM E23, ASTM A370, and ASTM D256 govern the exact testing procedure and test specimen requirements for each type of impact test, and for different material groups (e.g., metals vs. plastics).  Different materials testing standards ASTM E23 ASTM A370 ASTM D256 ASTM E23 outlines ASTM A370 is an umbrella spec The international standard for standards for impact used to cover assorted mechanical determination of the impact testing on steel specimens. Tests strength of plastic and insulation testing using both the included under the specification materials. The ASTM D256 standard Charpy and Izod methods. are tensile tests, bend tests, describes impact testing using the ASTM E23/ISO 148-1: These compression tests, impact tests Izod test method for determination standards govern impact and hardness tests. ASTM of the impact strength and notched testing for metals. D256/ISO 180: These standards impact strength of plastics. ASTM govern impact testing for plastics. A370/ASTM E208: This standard governs impact testing for steel materials. How Does Impact Test Work? An impact test works by striking a properly prepared and fixtures test specimen with a weight, either from the side or from above. For Charpy and IZOD impact tests, a pendulum with a weighted hammer is released from a specific height. The arc of its motion strikes the vertically oriented test specimen on its side. For drop-weight impact tests and dynamic tear tests, a weight is guided by rails and dropped directly onto a test specimen from above. For each type of impact test, a notch is cut into the test specimen, forcing the fracture of the specimen to occur at a repeatable location. What Are the Different Types of Impact Testing? 2. IZOD The Izod impact test is similar to the Charpy test in that a weighted pendulum hammer strikes a test specimen containing a V-shaped notch. An Izod impact testing apparatus which is essentially identical to a Charpy impact testing machine - is used to determine Izod impact strength. The primary differences between the Izod and Charpy impact tests are the size of the test specimen, how it is restrained, and which side is struck by the pendulum hammer. The Izod test, governed by ASTM D256, is most commonly used for thermoplastics. However, it can also be used for metals. Like the Charpy test, the Izod test is used to determine a material's toughness and its ductile-to-brittle 1. Charpy transition temperature. The Charpy impact test, also known as the V-notch test, is a type of impact test where a weighted pendulum hammer is released from a specified height and strikes the part. A Charpy impact testing apparatus, a device with a pendulum with various locking points at specified heights and a fixture to hold the test specimen, is used to determine Charpy impact strength. The Charpy impact test is most commonly used for ductile materials such as metals and thermoplastics. The test can be conducted at different temperatures and is often used to determine the ductile-to-brittle transition temperature of a material.  4. Dynamic Tear Test The dynamic tear test is similar to the drop-weight impact test. In the dynamic tear test, a notched test specimen is simply supported on both ends. A weight is dropped on the face opposite the notched side, and subjecting the test specimen to a bending impact load and 3-point bending. The primary difference between drop-weight-impact 3. Drop-Weight Impact Test testing and dynamic tear testing is that dynamic tear testing is often used for test specimens with a thickness The drop-weight impact test, also known as the Pellini test, uses a less than 5/8" while drop-weight impact testing is for test weight suspended over a simply supported horizontal test specimens thicker than 5/8". specimen and then dropped to produce the impact. A tube or rails guide the weight during its "free-fall" onto the specimen. Unlike Charpy and Izod tests, the height of the weight before and after it strikes the test specimen cannot be used to determine the energy absorbed by the test specimen. Instead, results only pass or fail since energy absorbed by the test specimen cannot be adequately determined. Fracture is not the only criterion for failure, deformation or the formation of a crack can also be considered a failure. WHAT IS DESTRUCTIVE TESTING? Destructive testing (often abbreviated as DT) is a test method conducted to find the exact point of failure of materials, components, or machines. During the process, the tested item undergoes stress that eventually deforms or destroys the material. Naturally, tested parts and materials cannot be reused in regular operation after undergoing destructive testing procedures. The need for destructive testing Materials that undergo destructive testing are damaged due to the test procedures. Still, destructive testing has many legitimate use cases. Oftentimes, destructive testing and using materials of specific characteristics come as a regulatory requirement. The reality is that machines and materials have physical and chemical characteristics that are not suitable for all conditions. For instance, metals that corrode easily are not suitable for use in extremely humid environments. Destructive testing is conducted by specialized researchers, scientists, and technicians. Who conducts it is determined by the type of destructive testing to be done. Generally, destructive testing is done by: Material scientists Metallurgical and polymer engineers Chemistry and electrochemical process experts Failure analysis experts Quality control analysts Regulatory compliance experts WHAT IS FATIGUE TESTING? A fatigue test helps determine a material's ability to withstand cyclic fatigue loading conditions. By design, a material is selected to meet or exceed service loads that are anticipated in fatigue testing applications. Cyclic fatigue tests produce repeated loading and unloading in tension, compression, bending, torsion or combinations of these stresses. Fatigue tests are commonly loaded in tension - tension, compression - compression and tension into compression and reverse. What is the Purpose of Fatigue Testing? Usually the purpose of a fatigue test is to determine the lifespan that may be expected from a material subjected to cyclic loading, however fatigue strength and crack resistance are commonly sought values as well. The fatigue life of a material is the total number of cycles that a material can be subjected to under a single loading scheme. A fatigue test is also used for the determination of the maximum load that a sample can withstand for a specified number of cycles. All of these characteristics are extremely important in any industry where a material is subject to fluctuating instead of constant forces. How to Perform a Fatigue Test? To perform a fatigue test a sample is loaded into a fatigue tester or fatigue test machine and loaded using the pre- determined test stress, then unloaded to either zero load or an opposite load. This cycle of loading and unloading is then repeated until the end of the test is reached. The test may be run to a pre-determined number of cycles or until the sample has failed depending on the parameters of the test.  Play + What is Corrosion Prevention and Control? Corrosion is the degradation or deterioration of materials, usually metals, due to chemical or electrochemical reactions with their environment.  Three factors govern corrosion The metal from which the 1 component is made. Prevention processes are unable to prevent the inevitable failure of the component by corrosion; they only slow down the process to a point where the The protective treatment the 2 component surface receives. component will have worn out or been discarded for other reasons before failing due to corrosion. Let's now look at the three ways in which metals corrode. The environment in which 3 the component is kept.  Three ways in which metals corrode Dry Corrosion Wet Corrosion Galvanic Corrosion This is the direct oxidation This occurs when two dissimilar This occurs in two ways: metals, such as iron and tin or iron of metals which occurs 1. The oxidation of metals in and zinc, are in intimate contact. when a freshly cut surface the presence of air and moisture, as in the They form a simple electrical cell in reacts with the oxygen of rusting of ferrous metals. which rain, polluted with dilute 2. The corrosion of metals by atmospheric acids, acts as an the atmosphere. electrolyte as generated and reaction with the dilute acids in rain due to the burning of fossil fuels (acid rain) - for circulates within the system. example, the formation of the carbonate Corrosion occurs with (depending upon its position in the 'patina' on copper. This is the characteristic electrochemical series) being eaten green film seen on the copper clad roofs of away. some public buildings.  Three factors govern corrosion The metal from which the 1 component is made. Prevention processes are unable to prevent the inevitable failure of the component by corrosion; they only slow down the process to a point where the The protective treatment the 2 component surface receives. component will have worn out or been discarded for other reasons before failing due to corrosion. Let's now look at the three ways in which metals corrode. The environment in which 3 the component is kept.  Types of Corrosion Galvanic Stress Corrosion Corrosion It has already been stated that Corrosion takes place in these regions when two dissimilar metals come of high energy and the locked-up into intimate association in the stresses give rise to the formation of presence of an electrolyte that a cracks which grow progressively with simple electrical cell is formed the continuance of corrosion. Atmospheric resulting in the eating away of one or other of the Corrosion metals. Any metal exposed to normal atmospheric conditions become covered with an invisible, thin film of moisture  Impingement Corrosion Fatigue Corrosion refers to the combined effects of As might be expected, any mechanical abrasion and chemical component which is subjected corrosion on a metallic surface. to alternating stresses and is working in conditions which Fretting Corrosion promote corrosion may fail at a stress well below the normal fatigue limit (3.72). is allied to corrosion fatigue and occurs particularly where closely fitting machine parts are subjected to vibrational stresses.  Factors affecting Corrosion 1 Structural Design 4 Composition and structure 2 Environment 5 Temperature PREVENTION OF CORROSION The huge annual loss due to corrosion is a national 3 Applied or internal stresses waste and should be minimized materials already exist which, if properly used, can eliminate 80% of corrosion loss proper understanding of the basics of corrosion and incorporation in the initial design of metallic structures is essential METHODS 1. MATERIAL SELECTION Metals and alloys :The most common method of preventing corrosion is the selection of the proper metal or alloy for a particular corrosive service. Mediums and corrosion Resistant Metals 1) Very Oxidizing Medium nitric acid, ( St. Steels ). 2) Caustic Solutions , (Ni & Ni-alloys ). 3) HCl , ( Monel alloy ). 4) Hot HCl , ( Hastelloys –chlorimets ). 5) Dilute H 2SO 4, ( lead ). 6) Oxidizing mediums , ( Al-alloy ). 7) Distilled water , ( Tin ). 8) Hot strong oxidizing solutions , ( Ti ). 9) For all conditions except for HF , ( Ta ). 10) Concentrated H 2SO 4, ( carbon steel ). Metal purification :The corrosion resistance of a pure metal is usually better than of one containing impurities or small amounts of other elements.However , pure metals are usually expensive and are relatively soft and weak. Nonmetallics:- Solid nonmetallic construction and sheet linings or coverings of substantial thickness ( to differentiate from paint coatings ).They are rubbers plastics ceramics carbon and graphite wood Rubbers & plastics are weaker , softer , and more resistant to chloride ions and hydrochloric acid than metals and alloys , but less resistant to sulfuric acid and oxidizing acids ( e.g. nitric acid ) , less resistance to solvents , low temp. limitations. Ceramics possess excellent corrosion and high temp. resistance. but brittle and low tensile strength. Carbons shows good corrosion resistance , electrical and heat conductivity , but they are fragile. Wood is attacked by aggressive environments. 2. Alteration of Environment Typical changes in medium are : Lowering temperature - but there are cases where increasing T decreases attack. E.g hot, fresh or salt water is raised to boiling T and result in decreasing 02 solubility with T. Decreasing velocity - exception; metals & alloys that passivate (e.g stainless steel) generally have better resistance to flowing mediums than stagnant. Avoid very high velocity because of erosion- corrosion effects. Removing oxygen or oxidizers - e.g boiler feedwater was deaerated by passing it thru a large mass of scrap steel. Modern practice - vacuum treatment, inert gas sparging, or thru the use of oxygen scavengers. However, not recommended for active-passive metals or alloys. These materials require oxidizers to form protective oxide films. Changing concentration - higher concentration of acid has higher amount of active species (H ions). However, for materials that exhibit passivity, effect is normally negligible 3. Environment factors affecting corrosion design Dust particles and man-made pollution - CO, NO, methane, etc. Temperature - high T & high humidity accelerates corrosion Rainfall - excess washes corrosive materials and debris but scarce may leave water droplets Air pollution - Nacl, SO, sulfurous acid, etc. Humidity - cause condensation 3. Design Do's & Don'ts Wall thickness - allowance to accommodate for corrosion effect. Avoid excessive mechanical stresses and stress concentrations in components exposed to corrosive mediums. Esp when using materials susceptible to SCC. Avoid galvanic contact / electrical contact between dissimilar metals to prevent galvanic corrosion. Avoid sharp bends in piping systems when high velocities and/or solid in suspension are involved - erosion corrosion Avoid crevices - e.g weld rather than rivet tanks and other containers, proper trimming of gasket, etc. Avoid sharp corners - paint tends to be thinner at sharp corners and often starts to fail. Provide for easy drainage (esp tanks) - avoid remaining liquids collect at bottom. E.g steel is resistant against concentrated sulfuric acid. But if remaining liquid is exposed to air, acid tend to absorb moisture, resulting in dilution and rapid attack occurs. Avoid hot spots during heat transfer operations - localized heating and high corrosion rates. Hot spots also tend to produce stresses - SCC failures. Design to exclude air — except for active-passive metals and alloys coz they require 0, for protective films. 4. Protective Coatings / Wrapping Provide barrier between metal and environment. Coatings may act as sacrificial anode or release substance that inhibit corrosive attack on substrate. Metal coatings : Noble - silver, copper, nickel, Cr, Sn, Pb on steel. Should be free of pores/discontinuity coz creates small anode-large cathode leading to rapid attack at the damaged areas. Sacrificial - Zn, Al, Cd on steel. Exposed substrate will be cathodic & will be protected. Application - hot dipping, flame spraying, cladding, electroplating, vapor deposition, etc. Surface modification - to structure or composition by use of directed energy or particle beams. E.g ion implantation and laser processing. Inorganic coating : cement coatings, glass coatings, ceramic coatings, chemical conversion coatings. Chemical conversion - anodizing, phosphatizing, oxide coating, chromat Organic coating : paints, lacquers, varnishes. Coating liquid generally consists of solvent, resin and pigment. The resin provides chemical and corrosion resistance, and pigments may also have corrosion inhibition functions. Electrochemical Nature of Aqueous Corrosion  For metallic materials, the corrosion process is normally electrochemical, i.e, a chemical reaction in which there is transfer of electrons from one chemical species to another. Aqueous corrosion is an electrochemical reaction of materials due to a wet environment, resulting in the deterioration Preterial and its vital properties. The hypothetical metal M that has a valence number of n (or n valence electrons) may experience oxidation according to the reaction: M → Mn+ + ne- in which M becomes an "n+" positively charged ion and in the process losses its "n" valence electrons (e-); is used to symbolize an electron. Other examples in which oxidation are: Fe → Fe2+ + 2e- Al → AI3+ + 3e- The site at which oxidation takes place is called the anode; oxidation is sometimes called an anodic reaction. The electrons generated from each metal atom that is oxidized must be transferred to and become a part of another chemical species in what is termed are duction reaction. Or a metal may be totally reduced from an ionic to aneutral metallic state according to: Nn+ + ne- → N For example, some metals undergo corrosion which have a high concentration of hydrogen (H) ions; the H ions are reduced as follows: 2H+ + 2e- → H2 The location at which reduction occurs is called the cathode.  Corrosion or anodic reaction of metals: M → Mn+ + ne- (general corrosion reaction ofa metal) Fe → Fe2+ + 2e- (iron corrosion) Al → Al+3 + 3e- (aluminum corrosion) Cu → Cu+2 + 2e- (copper corrosion)  Common cathodic reactions: near the surface of seawater: O2 + H2O + 4e- → 4OH- in de-aerated water: 2H2O + 2e- → H2 + 2OH- in aerated acids: O2 + 4H+ + 4e+ → 4H2O- in general: N+n + ne- → N  In de-aerated water (oxygen is removed): The nail in the de-aerated tube -Anodic Reaction: Fe→ Fe+2 + 2e- -Cathodic reaction (water without dissolved O2): 2H2O + 2e- → H2 + 2OH- -Overall: Fe + 2H2O → 2Fe(OH)2 + H2 THANK YOU!