Fundamental Types Of Distortion Engineering Essay

Fundamental Types Of Distortion Engineering Essay The high localised heating required in welding joint edges cause non-uniform stresses in the component and lead to expansion and contraction of the heated material. Initially, compressive stresses are created in the surrounding cold parent metal when the weld pool is formed due to the thermal expansion of the hot metal (heat affected zone) adjacent to the weld pool. However, tensile stresses occur on cooling when the contraction of the weld metal and the immediate heat affected zone is resisted by the bulk of the cold parent metal. The magnitude of thermal stresses induced into the material can be seen by the volume change in the weld area on solidification and subsequent cooling to room temperature. For example, when welding CMn steel, the molten weld metal volume will be reduced by approximately 3% on solidification and the volume of the solidified weld metal/heat affected zone (HAZ) will be reduced by a further 7% as its temperature falls from the melting point of steel to room temperature. If the stresses generated from thermal expansion/contraction exceed the yield strength of the parent metal, localised plastic deformation of the metal occurs. Plastic deformation causes a permanent reduction in the component dimensions and distorts the structure. Fundamental Types of Distortion Three fundamental dimensional changes that occur during the welding process cause distortion in fabricated structures: 1. Transverse shrinkage perpendicular to the weld line 2. Longitudinal shrinkage parallel to the weld line 3. Angular distortion (rotation around the weld line) These dimensional changes are shown in 1 and are classified by their appearance as follows: (a) Transverse shrinkage. Shrinkage perpendicular to the weld line (b) Angular change (transverse distortion). A non-uniform thermal distribution in the thickness direction causes distortion (angular change) close to the weld line. (c) Rotational distortion. Angular distortion in the plane of the plate due to thermal expansion. (d) Longitudinal shrinkage. Shrinkage in the direction of the weld line. (e) Longitudinal bending distortion. Distortion in a plane through the weld line and perpendicular to the plate. (f) Buckling distortion. Thermal compressive stresses cause instability when plates are thin. Figure Various types of weld distortion Contraction of the weld area on cooling results in both transverse and longitudinal shrinkage. Non-uniform contraction (through thickness) produces angular distortion in addition to longitudinal and transverse shrinkage. For example, in a single V butt weld, the first weld run produces longitudinal and transverse shrinkage and rotation. The second run causes the plates to rotate using the first weld deposit as a fulcrum. Hence, balanced welding in a double side V butt joint can be used to produce uniform contraction and prevent angular distortion. Similarly, in a single side fillet weld, non-uniform contraction produces angular distortion of the upstanding leg. Double side fillet welds can therefore be used to control distortion in the upstanding fillet but because the weld is only deposited on one side of the base plate, angular distortion will now be produced in the plate. Longitudinal bowing in welded plates happens when the weld centre is not coincident with the neutral axis of the section so that longitudinal shrinkage in the welds bends the section into a curved shape. Clad plate tends to bow in two directions due to longitudinal and transverse shrinkage of the cladding; this produces a dished shape. Dishing is also produced in stiffened plating. Plates usually dish inwards between the stiffeners, because of angular distortion at the stiffener attachment welds. In plating, long range compressive stresses can cause elastic buckling in thin plates, resulting in dishing, bowing or rippling. Distortion due to elastic buckling is unstable: if you attempt to flatten a buckled plate, it will probably snap through and dish out in the opposite direction. Twisting in a box section is caused by shear deformation at the corner joints. This is caused by unequal longitudinal thermal expansion of the abutting edges. Increasing the number of tack welds to prevent shear deformation often reduces the amount of twisting. Angular Distortion (Hirai and Nakamura 1955) conducted an investigation to determine the values of the angular change in a free joint and the coefficient of rigidity for angular changes under various conditions. 2shows the values of angular change as a function of plate thickness, t (mm), and weight of electrode consumed per weld length, w (g/cm). In order to convert from w to the size of the fillet weld, Df (mm), the following formula may be used: Where ? = density of weld metal, ?d = deposition efficiency. The fillet size, Df, is commonly used in design work, while w is easy to determine in a welding experiment. Figure Angular change of a free fillet weld in steel The results shown in 2 were obtained using covered electrodes 5mm in diameter. The maximum angular changes were obtained when the plate thickness was around 9mm. Then the plate was thinner, the amount of angular change was reduced with the plate thickness. This is because the plate was heated more evenly in the thickness direction, thus reducing the bending moment. When the plate was thicker than 9mm, the amount of angular change was reduced as the plate thickness increased because of increased rigidity. Previous two dimensional investigations (Duffy 1970; Shin 1972) of out-of-plane distortion of welded panel structures have shown that distortion increases with span length, and size of fillet weld. The investigations also indicated that there is a peak in distortion around 10mm plate thickness with lower distortion for thicknesses of 6mm and 14mm. Buckling Distortion When thin plates are welded, residual compressive stresses occur in areas away from the weld and cause buckling. Buckling distortion occurs when the specimen length exceeds the critical length for a given thickness in a given specimen size. It is important to determine whether distortion is caused by buckling of bending. Buckling distortion differs from bending distortion in that: 1. There is more than one stable deformed shape 2. The amount of deformation in buckling distortion is much greater Since the amount of buckling distortion is large, the best way to avoid it is to properly select such structural parameters as plate thickness, stiffener spacing and welding parameters. Extensive experimental and analytical investigations described in (Masubuchi 1970) conducted at Kawasaki heavy Industry clearly indicate the existence of a critical buckling heat input for given conditions. The critical buckling heat input decreases as plate thickness decreases and free span increases. For a given panel size the critical values for the heat input, are not affected by plate thickness. The critical heat input for buckling is little affected by the difference in welding process. Longitudinal and Transverse Shrinkage Twisting Contraction of the weld area on cooling results in both transverse and longitudinal shrinkage, whereas non-uniform contraction (through thickness) produces angular distortion. For example, in a single V butt weld, the first weld run produces longitudinal and transverse shrinkage and rotation. The second run causes the plates to rotate using the first weld deposit as a fulcrum. Hence, balanced welding in a double side V butt joint can be used to produce uniform contraction and prevent angular distortion. Similarly, in a single side fillet weld, non-uniform contraction produces angular distortion of the upstanding leg. Double side fillet welds can therefore be used to control distortion in the upstanding fillet but because the weld is only deposited on one side of the base plate, angular distortion will now be produced in the plate. Residual Stress The temperature distribution in the weldment is not uniform as a result of local heating (by most welding processes), and changes that take place as welding progresses. Heat-affected zones of the weldment and the base metal immediately adjacent to the welded area are at a temperature substantially above that of the unaffected base metal. Compressive stresses are created in the surrounding cold parent metal, when the weld pool is formed due to the thermal expansion of the hot metal (heat affected zone) adjacent to the weld pool. As the molten pool solidifies and shrinks, it begins to exert shrinkage stresses on the surrounding weld metal and heat-affected zone. However, tensile stresses occur on cooling when the contraction of the weld metal and the immediate heat affected zone is resisted by the bulk of the cold parent metal. Residual stresses in weldments have following two major effects: First, they produce distortion. Distortion is caused when the heated weld region contracts non-uniformly, causing shrinkage in one part of the weld to exert eccentric forces on the weld cross-section. The weldment strains elastically in response to these stresses. The distortion may appear in butt joints both as longitudinal and transverse shrinkage and as angular change (rotation) when the face of the weld shrinks more than the root. The latter change produces transverse bending in the plates along the weld length. Distortion in fillet welds is similar to that in butt welds. Transverse and longitudinal shrinkage as well as angular distortion results from the unbalanced nature of the stresses in these welds. Since fillet welds are often used in combination with other welds in a weldment, the specific resulting distortion may be complex. Secondly, residual stresses may be the cause of premature failure in weldments. If the stresses generated from thermal expansion/contraction exceed the yield strength of the parent metal, localised plastic deformation of the metal occurs. Plastic deformation causes a permanent reduction in the component dimensions and distorts the structure. Residual stresses The residual stresses in a component or structure are stresses caused by incompatible internal permanent strains. They may be generated or modified at every stage in the component life cycle, from original material production to final disposal. Welding is one of the most significant causes of residual stresses and typically produces large tensile stresses whose maximum value is approximately equal to the yield strength of the materials being joined, balanced by lower compressive residual stresses elsewhere in the component. Tensile residual stresses may reduce the performance or cause failure of manufactured products. They may increase the rate of damage by fatigue, creep or environmental degradation. They may reduce the load capacity by contributing to failure by brittle fracture, or cause other forms of damage such as shape change or crazing. Compressive residual stresses are generally beneficial, but cause a decrease in the buckling load. Residual stresses may be measured by non-destructive techniques, including X-ray diffraction, neutron diffraction and optic magnetic and ultrasonic methods; by locally destructive techniques, including hole drilling and the ring core and deep hole methods; and by sectioning methods including block removal, splitting, slicing, layering and the contour method. The selection of the optimum measurement technique should take account of volumetric resolution, material, geometry and access. Prediction of residual stresses by numerical modelling of welding and other manufacturing processes has increased rapidly in recent years. Modelling of welding is technically and computationally demanding, and simplification and idealisation of the material behaviour, process parameters and geometry is inevitable. Numerical modelling is a powerful tool for residual stress prediction, but validation with reference to experimental results is essential. Allowing for residual stresses in the assessment of service performance varies according to the failure mechanism. It is not usually necessary to take account of residual stresses in calculations of the static strength of ductile materials. Design procedures for fatigue or buckling of welded structures usually make appropriate allowances for weld-induced residual stresses, and hence it is not necessary to include them explicitly. Residual stresses have a major effect on fracture in the brittle and transitional regimes, and hence the stress intensity, K, or energy release rate, J, due to residual stresses must be calculated and included in the fracture assessment. K or J may be obtained as a function of stress distribution, crack size and geometry by various methods, including handbook solutions, weight functions, and finite element analysis. Residual stresses in as-welded structures may be minimised by appropriate selection of materials, welding process and parameters, structural geometry and fabrication sequence. Residual stresses may be reduced by various special welding techniques including low stress non-distortion welding (LSND), last pass heat sink welding (LPHSW) or inter-run peening. They may be relaxed by thermal processes including postweld heat treatment and creep in service, or by mechanical processes including proof testing and vibratory stress relief. Different stress relief treatments are appropriate in different applications. The effectiveness of the treatment may be reduced or the residual stresses may be increased if the treatment is not applied properly. Specialised processes are available for inducing beneficial compressive residual stresses, including peening, shot blasting, induction heating stress improvement (IHSI), low plasticity burnishing (LPB) and mechanical stress improvement procedures (MSIP ).

Eucharist History :: essays research papers fc

Eucharist History -reenacts the closing events of jesus' life -links past-present-future one ceremony -powerful, meaningful ritual -last of the 3 sacraments of initiation -prescribed by christ -have to see the eucharist as body, not bread Eucharist celebrates -"a way of remembering" -daily reminder of Gods love -jesus shared bread at last supper/do this in memory of me -a thanksgiving feast -"eucharist" means giving thanx Ritual Meal -earliest form of rituals are eating and gathering -sacrifice meal -ritual not a routine -builds on the symbolism of a ritual mean Sign and Symbols -symbol of gods love for us -jesus' body -last supper/banquet -welcome others to participate in the eucharist -unfilled celebration -if we went to mass on sunday, it would make the rest of the week more meaningful -unified body -it is the most commonly received sacrament, most pivotal of 7 -as a community, we celebrate the presence of christ in the eucharist -bread: basic food for most people/closely assoc with nature human work Vestements -white/purple/black robe Words -"Do this in Memory of Me." -"This is my body, which has been given up for you." ST. ROBERT'S CATHOLIC HIGH SCHOOL "THE EUCHARIST" BY: MARK HARNUM Presented to: Mr. DiMaio NRE 2A0-09 Monday November 29 , 1993 THE EUCHARIST Thesis: The Eucharist is a sign of Jesus' death, and how He gave himself up for us, and how we experience Him through His body. History of the Eucharist The Eucharist is a Jewish Ritual of worship. It dates back to the Last Supper, where Jesus celebrated a typical Jewish community meal with His friends. Sharing a meal with family, (very important to the Jews) also dates back to the Passover Meal. This is called the Liturgy of the Eucharist, and the early Christians added Jewish synagogue service and then became the Liturgy of the Word. The Eucharist is a sacrament, and is also a ritual. It is a repeated sacrament, and is the most frequently used among all sacraments. It is "a way of remembering" and a daily reminder if God's love. Jesus at the Last Supper shared bread with us, and said "Do this in Memory of Me." This is why we have bread, because it represents Jesus' body, and how He gave Himself up for us. The first little while of the Church, the "Mass was celebrated as a friendship meal called agape." Christians shared brought food to the house where they were assembled, but as the numbers increased, the meal was cut down to bread and wine. Today, the offertory collection echoes the early years of the spirit giving at the Eucharist. It is living bread that came down from heaven.

Article Review of “Fat and Happy” Essay

In â€Å"Fat and Happy: In Defense of Fat Acceptance,† Mary Ray Worley offers a poignant account of her participation in a conference held by the National Association to Advance Fat Acceptance. She compares attending this conference with visiting another planet. Until she had the opportunity to visit this other planet, she had not realized just how ostracized she felt. (Worley, element 1). Her participation in this conference made her realize that â€Å"20th century American society† (Worley, element 4) is very much responsible for the shame that she and other overweight individuals have been made to feel. While there are several aspects of society that contribute to the alienation of individuals who are overweight, Worley suggests that the medical field bears a great deal of the responsibility: â€Å"Although the data gathered for most current studies indicate that body size is primarily determined by one’s genetic makeup, most researchers conclude–in spite of their own findings–that fat individuals should try to lose weight anyway† (Worley, element 3). She than goes on to argue that oftentimes attempts to diet only result in more weight gain. Worley marvels that â€Å"apparently [scientists] cannot bring themselves to say that since body size is largely a result of one’s genetic makeup it’s best to get on with the business of learning to live in the body you have, whatever its size† (Worley, element 5). She also claims that doctors often make the situation worse: â€Å"Regardless of the ailment†¦your doctor may put you on a diet before she treats your cough† (Worley, element 6). I believe that Worley makes a good point regarding the medical profession, but there is indeed a great deal of research that links obesity with increased heart problems among other things, which Worley ignores in this essay. In her uplifting conclusion, Worley encourages overweight individuals to love their bodies despite what society may say about them. You’re entitled to the space you take up. You can find clothes that show off the gorgeous person you are, you can play and dance without self-consciousness, you can be proud of yourself and never dread unwanted attention, you can be a brave pioneer and a friend to those who have suffered on planets less kind and less joyous than this one (Worley, element 2). In light of the many forces that are stacked against overweight individuals in our society, Worley’s words of encouragement are astute and empowering.

Microeconomics ( From The Greek Prefix Meaning, Large, And...

Summary Macroeconomics (from the Greek prefix macro- meaning large and economics) is a branch of economics dealing with the performance, structure, behaviour, and decision-making of an economy as a whole, rather than individual markets. This includes national, regional, and global economies.[1][2] With microeconomics, macroeconomics is one of the two most general fields in economics. Macroeconomists study aggregated indicators such as GDP, unemployment rates, and price index, and the interrelations among the different sectors of the economy, to better understand how the whole economy functions. Macroeconomists develop models that explain the relationship between such factors as national income,†¦show more content†¦Macroeconomic Performances Introduction Economics is the social science that seeks to describe the factors which determine the production, distribution and consumption of goods and services. Economics focuses on the behaviour and interactions of economic agents and how economies work. Consistent with this focus, primary textbooks often distinguish between microeconomics and macroeconomics(wiki). Microeconomics examines the behaviour of basic elements in the economy, including individual agents and markets, their interactions, and the outcomes of interactions. Individual agents may include, for example, households, firms, buyers, and sellers. Macroeconomics analyses the entire economy (meaning aggregated production, consumption, savings, and investment) and issues affecting it, including unemployment of resources (labor, capital, and land), inflation, economic growth, and the public policies that address these issues (monetary, fiscal, and other policies). Evaluation of macroeconomic performance The macroeconomic performance of a given country is evaluated by two primary tools, the fiscal and monetary policies. Fiscal policies are the economic policies that are formulated by the government to stimulate economic growth in the country (Argy, 2013). It primarily