COMSATS Institute of Information Technology, Sahiwal

“Is the experimental stress analysis is feasible in plastic industry?If it is not then why not?If it is then how and what parameters can be necessarily modified as

compared to metal industry??”

Submitted to

Dr. Muhammad Rizwan

Assistant Professor

CIIT, Sahiwal

Submitted by

Danish jalil

Fa11-BME-B3-020

Grade-----------------------

Checked By ---------------

Department of Mechanical Engineering

Introduction

Plastic parts often fail because they were not design properly. Mechanical stresses placed upon a part can cause a part to fail if the part is not designed appropriately to distribute the stresses evenly across the part. If a part contains areas where stresses can concentrate, the part will likely fail. When failure occurs, our experts can analyze the situation and provide expert witness services regarding improper part design. Our computerized part design capabilities allow us to vividly explain why a particular part failed due to improper part design[1].

Is experimental stress analysis is feasible in plastic industry?

Yes experimental stress analysis is feasible in plastic industry…Normally in plasicindustry thematrerials are mostly plastic type and Photoelasticity is an experimental technique for stress and strain analysis that isparticularly useful for members having complicated geometry, complicated loading conditions,or both. For such cases, analytical methods (that is, strictly mathematical methods) may becumbersome or impossible, and analysis by an experimental approach maybe more appropriate.While the virtues of experimental solution of static, elastic, two-dimensional problems are nowlargely overshadowed by analytical methods, problems involving three-dimensional geometry,multiple-component assemblies, dynamic loading and inelastic material behavior are usuallymore amenable to experimental analysis[2].

Material Selection

Occasionally the material selected for manufacture of the part does not have sufficient mechanical strength or chemical resistance properties needed for the part to stand up to the demands of an application in which the part is being used. When failure of a plastic part occurs because the wrong material was used, out experts can explain why the material was wrong and what material should have been used to manufacture the part [3].

.Material Contamination

In today’s world, because of global competition, many plastic parts are manufactured in third world countries. Third world countries often lack good manufacturing practices (GMP) including poor quality control (QC) practices. As a result, poor plastic part quality including

material contamination, are leading causes of failure. Our experts utilize the latest forensic analysis technology including scanning electron microscopy (SEM), digital imaging technology, gas chromatography – mass spectroscopy (GC-MS), Fourier Transform Infrared Spectroscopy (FTIR), differential scanning calorimetry (DSC), and electron dispersive x-ray spectroscopy (EDS) to identify root causes of failure of materials and the role material contamination and poor manufacturing practices may have played in causing a plastic part to fail.

Normally in plasicindustrythematrerials are mostly plastic type and Photoelasticity is an experimental technique for stress and strain analysis that isparticularly useful for members having complicated geometry, complicated loading conditions,or both. For such cases, analytical methods (that is, strictly mathematical methods) may becumbersome or impossible, and analysis by an experimental approach maybe more appropriate.While the virtues of experimental solution of static, elastic, two-dimensional problems are nowlargely overshadowed by analytical methods, problems involving three-dimensional geometry,multiple-component assemblies, dynamic loading and inelastic material behavior are usuallymore amenable to experimental analysis[4].

The name photoelasticity reflects the nature of this experimental method: photo implies the use of light rays and optical techniques, while elasticity depicts the study of stresses and deformations in elastic bodies. Through the photoelastic-coating technique, its domain has extended to inelastic bodies, too.Photoelastic analysis is widely used for problems in which stress or strain information isrequired for extended regions of the structure. It provides quantitative evidence of highly stressedareas and peak stresses at surface and interior points ofthe structure — and often equallyimportant, it discerns areas of low stress level where structural material is utilized inefficiently.This chapter is intended to introduce the basic

concepts — to emphasize those elementsthat are fundamental to the photoelastic method. The details involving characteristics of specificphotoelastic materials — their formulation, optical and mechanical properties, machiningtechniques, etc. — and the details involved in the use of specialized auxiliary instruments andaccessories are not included. While such information is vitally important to the student ofphotoelasticity, it quickly becomes obsolete and is better disseminated by current technical papersand current manufacturers' literature [5].

6.2. PHOTOELASTIC BEHAVIOR

The photoelastic method is based upon a unique property of some transparent materials,in particular, certain plastics. Consider a model of some structural part made from a photoelasticmaterial. When the model is stressed and a ray of light enters along one of the directions ofprincipal stress, a remarkable thing happens. The light is divided into two component waves,each with its plane of vibration (plane of polarization) parallel to one of the remaining twoprincipal planes (planes on which shear stress is zero). Furthermore, the light travels along thesetwo paths with different velocities, which depend upon the magnitudes of the remaining twoPrincipal stresses in the material.

Photoelasticity is an experimental method to determine the stress distribution in a material. The method is mostly used in cases where mathematical methods become quite cumbersome. Unlike the analytical methods of stress determination, photoelasticity gives a fairly accurate picture of stress distribution, even around abrupt discontinuities in a material. The method is an important tool for determining critical stress points in a material, and is used for determining stress concentration in irregular geometries[6].

Two-dimensional photoelasticity

Photoelasticity

Photoelasticity can be applied both to three-dimensional and two-dimensional state of

stress. But the application of photoelasticty to the three-dimensional state of stress is more

involved as compared to the state of two-dimensional or plane-stress system. So the present

section deals with application of photoelasticity in investigation of a plane stress system. This

condition is achieved when the thickness of the prototype is much smaller as compared to

dimensions in the plane. Thus one is only concerned with stresses acting parallel to the plane of

the model, as other stress components are zero. The experimental setup varies from experiment

to experiment. The two basic kinds of setup used are plane polariscope and circular polariscope.

The working principle of two-dimensional photoelasticity allows the measurement of

retardation, which can be converted to the difference between the first and second principal

stress and their orientation. To further get values of each stress component, a technique called

stress-separation is required.Several theoretical and experimental methods are utilized to provide

additional information to solve individual stress components[7].

Destructive and Non destructive both are studied in Experimental stress anlaysisN.D.T can some

be possible to some extent as follows:

N.D.T In plastics:

Although it is possible to judge some defects in plastics using NDT techniques (like

infrared thermography) but to scan the entire specimen in detailed manner, destructive testing is

used.

.Inability of Plastics !!!:

The inability of plastics to respond different non-destructive testing techniques is due to

non-crystalline structure of plastics.

For example, in liquid penetrant inspection (technique of NDT), we can judge the extent

of crack along a particular dimension, but still we are not able to judge the further progress of

crack within the plastic. Unlike metals, which behave uniformly in all directions under specific

condition, plastics are unable to respond uniformly under a specific type of loading. So we have

to perform destructive testing to judge the overall effect of deficiencies in case of plastics. [8].

Application

Photoelasticity has been used for a variety of stress analyses and even for routine use in

design, particularly before the advent of numerical methods, such as for instance finite elements

or boundary elements. Digitization of polariscopy enables fast image acquisition and data

processing, which allows its industrial applications to control quality of manufacturing process

for materials such as glass and polymer. Dentistry utilizes photoelasticity to analyze strain in

denture materials[9].

Photoelastic model to validate the stiffener model. Isochromatic fringe patterns around a steel

platelet in a photo-elastic two-part epoxy resin.

Photoelasticity can successfully be used to investigate the highly localized stress state

within masonryor in proximity of a rigid line inclusion (stiffener) embedded in an elastic

medium. In the former case, the problem is nonlinear due to the contacts between bricks, while

in the latter case the elastic solution is singular, so that numerical methods may fail to provide

correct results. These can be obtained through photoelastic techniques[10].

Parameters modified in plastic industry as campared to metal industry:

More factor of safety: In plastics more factor of safety should be kept so that our material becomes safe and

sound.

High tensile strength

High tensile strength with proper structural design are required in it.

Less Weight Effective

Reduced part weight

less scrap

Highly repeatable in processing (less scrap)

Coats Effective

Lower manufacturing costs

Flexibility

Greater design flexibility (part consolidation)

Less packing Coast

Lower packaging and shipping costs

Tool life

Up to six times longer tool life.

Metal-to-PlasticTedency

Current metal-to-plastic trends focus on reducing weight, improving strength and

corrosion resistance, and consolidating multiple metal parts into one plastic part. Plastic parts can

be just as tough as metal parts and achieve the same tight tolerances, with fewer secondary

operations. In general, companies can expect to achieve an overall cost savings of 25% to 50%

by converting to plastic parts[11].

A comparison of the specific gravity values of metals to plastics shows how dramatic the difference in weight can be.

Design Freedom

Converting to plastic parts gives manufacturers more freedom in product design, including greater variety in material selection and being able to create more complex geometries. It is much easier to produce complex shapes out of plastic than metal, due to injection molds allowing for under-cuts, threads, ports, and tight tolerances allowing a net shape to be produced to the finish level specifications.“Plastics can be made to flow to produce thin-walled parts with uniform wall dimensions, replacing the more costly thicker-walled design features of most die-cast metal parts,” says Ken Glassen, vice president of engineering for Kaysun Corporation, an injection molder in Manitowoc, WI. “Multiple metal parts can be replaced by one injection-molded part made of tough engineered plastic, eliminating the need for fasteners and assembly.”Plastic parts can actually be stronger than metal parts by using engineering-grade materials with proper structural design. The ability to mold in features for structural strength such as ribs, bosses, and gussets when the part is originally produced (instead of fastening, welding, and gluing afterwards) can increase the total strength of the assembled part as well as reduce additional costs.“There are many more options available for materials and additives/fillers when using plastic instead of metal,” adds Glassen. “Converting from metal to plastic gives designers the ability to produce final net shape and dimensions, all in one process [12].”

Key considerations for type of plastic are:

Crystalline vs. amorphous: evaluate requirements such as chemical resistance, impact, flow,

processing, etc.

Additives: additives will affect strength, stiffness, temperature performance, appearance,

package requirements, and cost.

Carbon and stainless steel fillers improve conductive and/or shielding properties.

Lubricant fillers improve wear and friction properties.

Mineral fillers improve electrical performance, weighted feel, sound dampening, and higher

specific gravity and improve dimensional stability.

Impact modifiers improve toughness.

Acknowledgment

I am thankful to Dr. Muhammad Rizwan for assigning me such assignment which prove to be very interesting and helped in increase of my knowledge from industry point of view and about modern processes inuse for useful purposes.

Conclusion

In order to compete in today's very competitive environment, manufacturers put a lot of

emphasis on product differentiation while maintaining good margins and low cost. This

differentiation is done by design, visual appearance or by development of new functionalities

requiring miniaturized or more sophisticated systems. Part rationalization is another significant

trend in industries such as automotive, appliances, electronics and medical, as it increases end

product reliability and decreases inventories.For these reasons the use of plastics to replace metal

and other traditional materials is becoming a key strategy in many markets.This trend is

expanding rapidly due to the multiple benefits provided by plastics compared to metal. All of

them lead to significant productivity improvements and/or product differentiation. Experimental

stress analysis provide its applications for every type of materials whether it was metals and

plastics.

References

1. Oxford English Dictionary Second Edition on CD-ROM (v. 4.0) © Oxford University Press 2009

2. Jump up^ "Sinter" The Free Dictionary accessed May 1, 20143. ^ Jump up to:a Kingery, W. David; Bowen, H. K.; Uhlmann, Donald R. (April

1976). Introduction to Ceramics (2nd ed.). John Wiley & Sons, .4. . ScienceDirect. Retrieved 2011-09-30.5.  Salvatore Grasso et al. (2009). "Electric current activated/assisted sintering (ECAS): a

review of patents 1906–2008". Sci. Technol. Adv. Mater. (free download pdf)10 (5): 053001. doi:10.1088/1468-6996/10/5/053001.

6. Jump up^ Tuan, W.H.; Guo, J.K. (2004). Multiphased ceramic materials: processing and potential. Springer. ISBN 3-540-40516-X.

7. Jump up^ Hulbert, D. M. et al. The Absence of Plasma in‘ Spark Plasma Sintering’. Journal of Applied Physics 104, 3305 (2008).

8. Jump up^ Anselmi-Tamburini, U. et al. in Sintering: Nanodensification and Field Assisted Processes (Castro, R. & van Benthem, K.) (Springer Verlag, 2012).

9. ^ Jump up to:a b c Palmer, R.E.; Wilde, G. (December 22, 2008). Mechanical Properties of Nanocomposite Materials. EBL Database: Elsevier Ltd. ISBN 978-0-08-044965-4.

10.Jump up^ Smallman R. E., Bishop, Ray J (1999). Modern physical metallurgy and materials engineering: science, process, applications. Oxford : Butterworth-

11.^ Jump up to:a b c d e Mittemeijer, Eric J. (2010). Fundamentals of Materials Science The Microstructure–Property Relationship Using Metals as Model Systems. Springer Heidelberg Dordrecht London New York. pp. 463–496. ISBN 978-3-642-10499-2.

12.Jump up^ Kang, Suk-Joong L. (2005). Sintering: Densification, Grain Growth, and Microstructure. Elsevier Ltd. pp. 9–18. ISBN 978-0-7506-6385-4.

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