Eray Cavus 030060022 5th week

Layer Removal Method (Deformation measurement method)

Layer Removal Method (old)

The layer removal, progressive turning or boring, trepanning, chemical etch, modified layer removal and hole-drilling methods all rely on basically the same principle. The component is either machined, etched or drilled in stages so that the residual stresses are released producing relaxation deformations or strains which can be measured by mechanical methods or electrical resistance strain gauges and, after certain corrections, related to the initial residual stresses. Apart from the hole-drilling technique which is discussed in detail below, the other techniques of metal removal type are classed as destructive since the component cannot generally be used after the measurement procedure has been completed.

(Hearn, E., J., Mechanics of Materials: The Mechanics of Elastic and Plastic Deformation of Solids and Structural Materials, 3rd Ed., p.403)

Layer Removal Method(new) (better)

The layer removal method is a generalization of Stoney`s method. It involves observing the deformation caused by the removal of a sequence of layer of material. The method is suited t oflat plate and cylindrical specimens where the residual stresses are known to vary with depth from the surface, but to be uniform paralel to the surface. Figure illusterates examples of the layer removal method, (a) on a flat plate specimen, and (b) on a cylindrical specimen. The method involves measuring deformations on one surface, for example using strain gauges, as paralel layers of material are removed from the opposite surface. In the case of a hollow cylindrical specimen, deformation measurements can be made on either the outside or inside surface, while annular layre removed from the opposite surface. When applied to cylindrical specimens, the layer removal method is commonly called “Sachs`c Method”. The method is a general one; it is typically applied to metal specimens, eg., but can be applied to other materials, e.g., paperboard.

(Experimental and Applied Mechanics: Proceedings of the 2010 Annual Conference on Experimental and Applied Mechanics, Yazar: Tom Proulx,page:223)

Cross-linked Polymers (Material)

Cross-linked Polymers (old)(better)

For certain polymers, primary bonding occurs between branches and other molecules at certain connection points to form Cross-linked Polymers.Cross-linking occurs because a certain proporiton of the monomers used to form the polymer are capable of bonding to adjacent monomers on more than two sides, thus allowing branches from other molecules to attach.Lightly crossilinked structures are characteristic of elastomers.When the polymer is highly cross-linked we refer to it as having a network structure in effect , the entire mass is one gigantic macromolucule.Thermosetting plastics take this structure after cutting.

Thermosetting plastics and elastomers are cross-linked polmers.Cross-linking causes the polymer to become chemically set; the reaction cannot be reserved.The effect is to permanently change the strucrure of the polymer ; upon heating , it degrades or burns rather than melts.Thermosets possess a high degree of cross-linking , while elastomers possess a low degree of cross-linking.Thermosets are hard and brittle , while elastomers are elastic and resilient.

(Mikell P.Groover, Fundamentals of Modern Manufacturing , materials,processes, and systems third edition page 151-152)

 

Cross-linked Polymers (new)

When polymers are produced in which the polymer molecules are linked to each other at points other than than their ends, the polymers are said to be crosslinked (Fig). Crosslinking can be made to occur during the polymerization process by the use of appropriate monomers. It can also be brought about after the polymerization by various chemical reactions. The crosslinks between polymer chains can be of diffirent lengths depending on the crosslinks is sufficiently high, a three-dimensional or space network polymer is produced in which all the polymer chains in a sample have been linked together to form one giant molecule. Light crosslinking is used to impart good recovery (elastic) properties to polymers to be used as rubbers. High degrees of crosslinking are used to impart high rigidity and dimensional stability (under conditions of heat and stress) to polymers such as the phenol-formaldehyde and urea-formaldehyde polymers.

(Principles of polymerization, Yazar: George G. Odian, page:19)

Rake Angle (Machining Term)



Rake Angle (old)



A cutting tool has one or more sharp cutting edges and is made of a material that is harder than the work material. The cutting edge serves to separate a chip from the parent work material. Connected to the cutting edge are two surfaces of the tool: the rake angle and the flank. The rake face, which directs the flow of the newly formed chip, is oriented at a certain angle called the rake angle. It is measured relative to a plane perpendicular to the work surface. The rake angle can be positive, or negative.


(M. P. Groover, Fundamentals of Modern Manufacturing, p. 484)

Rake Angle(New) (Better)


Machinability tests have confirmed that when the rake angle along which the chip slides, called the true rake angle, is made larger in the positive direction, the cutting force and the cutting temperature will decrease. Also, the tool life for a given cutting speed will increase with increases in the true rake angle up to optimum value, after which it will decrease again. For turning tools which cut primarily with the side cutting edge, the true rake angle corresponds rather closely with the side rake angle except when taking shallow cuts. Increasing the side rake angle in the positive direction lowers the cutting force and the cutting temperature, while at the same time it results in a longer tool life or a higher permissible cutting speed up to an optimum value of the side rake angle. After the optimum value is exceeded, the cutting force and the cutting temperature will continue to drop; however, the tool life and the permissible cutting speed will decrease.


(Shop reference for students and apprentices, Yazar: Edward G. Hoffman,Christopher J. McCauley, 
 page:386)

Electrostatic Coating  (Coating Method)

Electrostatic Coating (Old)

Electro-coating is based on the electrostatic principle.The product to be
painted is an electrode of a high voltage circuit.A grid, whivh is positioned
close to and between the spray nozzles and the part, is used as the other
electrode. A DC current is applied to the two electrodes, and the part is
sprayed through the grid.The paint particles pick up ions and become charged
electrostaticaly.
The work electrodes attack the charged paint particles and are deposited on
the work. The efficiency of this method of spray-painting is much higher then
others.
(Harold V. Johnson, Manufacturing Process, p.478)

Electrostatic Coating (New)

Electrostatic coating is the application of charged paint particles to a workpiece with an opposite charge. Charged powdered particles or atomized liquid paint is initially projected toward the conductive workpiece by a mechanical or compressed air spraying method and then accelerated toward the workpiece by the powerful electrostatic charge.

Process Characteristics

·         Utilizes a hihg voltage applied to workpiece and sprayer

·         Is 95% paint-efficient due to reduced over-spray and better “wrap-around”

·         Can be an automatic or manual process

·         Materials can be in a powder or liquid form

·         Workpieces must beconductive

·         Workpieces are usually baked after coating.

Process Schematic

The workpiece is conveyed to the paint booth and electrostatically coated with a liquid or powder mixture via a spray nozzle. The powdered paint recovery unit recycles between 95% and 100% of the paint overspray. After coating, the workpiece is transferred to the baking oven for curing.

(Manufacturing processes reference guideYazar: Robert H. Todd,Dell K. Allen,Leo Alting, page:459)

Bending Test (Strength Test)

 

Bending Test(old)

Bending operations are used to form metal plates and sheets.The process of bending a rectangular cross section subjects the material to tensile stresses(and strains) in the outer half of bent section and compressive stresses in the inner half.If the material does nat fracture , it becomes permanently(plastically) bent.

Hard, brittle materials , which posses elasticity but little or no plasticity, are often ested by a method that subjects the specimen to a bending load.These metarials do not respond well to traditional tensile testing because of problems in preparing the test specimens and possible misalignment of the press jaws that hold the specimen.The bending test(also known as the flexure test) is used to test the strength of these materials, using a setup illustrated in the first diagram.In this procedure , a specimen of rectengular cross section is positioned between two supports, and a load is applied at its center.In this configuration, the test is called a three-point bending test.A four point configuration is also sometimes used.

(Mikell P.Groover, Fundamentals of Modern Manufacturing , materials,processes, and systems third edition page 49)

Bending Test (new) (better)

 The bending test is one of the commonest and simplest tests performed in bones. Basically, it consists of laying the extremities of the specimen on two metallic supports and applying a progressive vertical force in its center, so that the displacement can be recorded. This test is recommended when the main physiological forces supported by the specimen are in flexion. When force is applied, the bending of the sample gives rise to the formation of compression stress on the concave surface and traction stress on the convex surface.(fig) Likewise, in the interface between the two opposite tensions, there is no stress (neutral line). Common bendingtests are flexion at two points, three points and four points. For biological purposes the three-point and four-point tests are more used. The difference between them is that in a four-point bending test the streses are more evenly distributed in the specimen.

 

(Osteoporosis Research: Animal Models, Yazar: Gustavo Duque,Ken Watanabe, page:31)