Popular in Course
Popular in Engineering and Tech
This 10 page Class Notes was uploaded by Jerome Keeling II on Thursday October 29, 2015. The Class Notes belongs to EGR190 at Wright State University taught by Staff in Fall. Since its upload, it has received 15 views. For similar materials see /class/231109/egr190-wright-state-university in Engineering and Tech at Wright State University.
Reviews for FundamentalsofEngineeringandComputerScience
Report this Material
What is Karma?
Karma is the currency of StudySoup.
Date Created: 10/29/15
Pressure Vessels Figures from Mechanics ofMaterials by Higdon et 211 4th edition John Wiley and Sons 1985 Educational Objectives D l 9 E 4 Introduce the concept of stress and strain Introduce Hooke s law Young s modulus and Poisson s ratio Show basic equations for obtaining stresses in a thin walled pressure vessel Introduce electrical resistance strain gauges Measure internal pressure in a soda pop can using strain gauges Background Information 1 Stress The ability of a structural component to support a load depends on two factors the inherent strength of the material and the area over which the load is being supported The term stress is used to identify the intensity of force Stress cr Force F Area A Area A Nnnnn2 lbln2 orpsl m the conventlonal system ofumts made ofls not changed 2 Strain P vw w m deformatlon ls called plasne deformatlon Generally alonger me objectgreatens me h wd amount of defomauon Longitudlnal stram ls de ned as Change in Length AL Strain a 7 Original Length L0 L ltls umM umts or mmmm or lnenlnen 3 Hunke39s Law F F uquot M duhl letter Thls ls aproperty of llne matenal crEs The umts ofE are Pascal m 51 or psl m eonvenuonal umts 1n the gure above when a sness s ls applled the length ofthe cyllnderwlll change by an amount ALSL0 AE 1n othetvvotols L L L L L 4 LL ehange by less than about moon of the ongtnal length 4 Pnissnn39 Ratin 1n the gu e above when the length ofthe evltnolettneteases oltte to the applteanon of a sttess along tts axls thete ts a oleetease tn dtannetet ofthe evltnolet In othet vvotols the r tn amount oftransverse stxam ts ptopotttonal to the axlal sttatn a Pouson39s Ratio l 7 Saml Potsson s tatto ts umHess 5 Th39 alled Pressure Vessel e m w r h H w d w The tnstole of the ptessute vessel ts at ahtghetptessute than the outstole Thts tesults tn sttesses tn the eontatnet wall The eontatnetvvall staetehes evet so sltghtlv tn response to e staesses long evltnolets vvtth thett enols eappeol off and spheneal ptessute vessels A ptessute vessel thathas avvall thtekness less than about 110 ofthe dtannetet ofthe eontatnetts tt 4 t cyllndncal ptessute vessel cyllndncal ptessute vessel the axlal staess as and the hoop staess at The axlal anol hoop wdlrumf rwn Vr r n h l T w thtough the followmg equan ons thckness The hoop stress has twlce the magmde of the axlal stress 5 Eleccrlcal Resistance Strain Gauges By now you must be famlllar wlth the concept of eleetneal reclstanee Ohm s law states across lts ends The eleetneal reclstanee R15 slmply the retro of the voltage V andthe eurrentl R K I wlre R LL A cross seetlonal areals decreased the reslstanee of the wlre mcreases ln otherworols expenence a sham the strnn gauge deforms along Wth lt Thls deformation ls re eeted as apropomonal change tn the reclstanee of the strnn gauge Wheatstone s Brldge elreult shown below Wheatstone s Bridge Encapsulation CopperCoated Tabs Backing Threewire QuarterBridge Circuit Figures from Micromeasurments Group When all the resistors in the Wheatstone39s bridge circuit above have the same resistance the output voltage e0 will be zero When one of the arms of the bridge is replaced by a strain gauge then we have a Quarter Bridge circuit Let us assume the lead wires that connect the strain gauge to the rest of the bridge have no resistance RL 0 Now if the resistance of the strain gauge changes by AR then the output voltage is AR ea 2 E 4R6 where RG is the resistance of the strain gauge The corresponding strain is In the above equations E is the bridge excitation voltage GF is the gauge factor of the strain gauge and R is the nominal resistance of the strain gauge In our experiments we will set E 10Volts and for our gauges GF 212 and R 120 Q Procedures In this lab you will use electrical resistance strain gauges to measure the pressure inside a soda pop can The procedure is as below 1 2 E 4 Get your soda can from the TA Measure the diameter d of the can Use vemier calipers to measure the wall thickness ton the can that has been cut open Use sand paper to scrape of the paint on the can and mount two strain gauges one in the axial direction and one in the hoop direction Instructions on mounting strain gauges are in the appendix V39 Connect the two gauges to two channels of the strain gauge ampli er VishayMicromeasurment The ampli er contains the rest of the Wheatstone39s Bridge and the necessary amplifying circuit to convert resistance changes to strain The display shows the magnitude of strain in micrommmm of one channel Turn the excitation voltage to each of the channels you are using Selecting each channel in turn zero out the readings on the strain gauge indicators using the balance knob If you are not able to zero them out you have probably damaged the strain gauge during the mounting process or the wires have not been soldered properly If this happens use a multimeter to check the resistance across the wires and remount the gauges or resolder the lead wires if necessary After you have balanced both channels carefully open the can There will be change in the strain reading Record the change in aXial and hoop strains The measured strain values can be converted to the pressure inside the can before it was opened through the following equations 9 89 0 O p 4 Esa 41138 fa 2v d2 v Use values of E 70X109 Nmm2 and v 035 to calculate the pressure inside the can Since you have two independent strain measurements in the aXial and hoop directions you can determine the pressure two different ways Comment on any differences you may see Food for Thought When you microwave a hot dog why does the skin split along its length Appendix 0quot STrain gauge MounTing Ligthy draw alignmenT lines on The TesT surface on which The gauge is To be mounTed Place The gauge wiTh The quotshinyquot side up on a clean surface such as The Top of The plasTic box in which The sTrain gauges are packed Take a 4 inch piece of removable adhesive Tape and ligthy rub The nonsTicky side of The Tape againsT a meTallic surface To discharge sTaTic elecTriciTy Carefully place The Tape on The sTrain gauge Peal up The Tape aT a shallow angle 30 The sTrain gauge should come up wiTh The Tape Place The sTrain gauge and Tape on The TesT surface aT The desired locaTion using The previously marked lines for alignmenT You will be able To peal back The Tape and reposiTion The gauge if necessary STep 4 STep 5 AfTer you are saTisfied wiTh The alignmenT of The sTrain gauge peal The Tape back one more Time To lifT The gauge from The can surface Peal The Tape back an addiTional 12inch Apply a small amounT of caTalysT on The exposed dull surface of The sTrain gauge The caTalysT is a blue liquid Dip The brush ThaT is aTTached To The cap of The caTalysT boTTle in The caTalysT and Then wipe iT againsT The lip of The boTTle abouT 10 Times Apply The caTalysT on The gauge using smooTh sTrokes wiThouT sTopping on The gauge Apply one drop of The adhesive MBond 200 aT The seam beTween The Tape and The TesT surface abouT 12 inch from where The gauge is To be aTTached see iTem 6 above InsTrucTions and figures are based on informaTion in BulleTin 309D STudenT Manual for STrain Gauge Technology MeasuremenTs Group 1992 STep 6 7 5 v 65 STep 10 STep 11 9 Quickly aTTach The gauge on To The TesT surface by a smooTh wiping acTion on The Tape This will spread The glue uniformly over The gauge Be careful noT To geT glue on The skin 10 Apply genTle Thumb pressure on The gauge for 30 seconds 11 WaiT 1 minuTe and Then peal back The Tape The gauge should now sTay aTTached To The TesT surface 12 RepeaT sTeps 1 Through 11 for The oTher gauge 13 ATTach lead wires a Apply flux To The Terminals of The sTrain gauge and The lead wires b Apply a small drop of solder To The sTrain gauge Terminals and solder The wires in place Make sure The wires don39T cross and The gauge Terminals are noT shorTed ouT c Secure wires in place wiTh adhesive Tape 14 Check The resisTance across The ends of The lead wires using a digiTal mulTimeTer The resisTance should be 1209 If you geT a number much differenT from 1209 eiTher you have damaged The sTrain gauge during The mounTing process or The wires have noT been soldered properly RemounT The gauge or resolder The lead wires if necessary
Are you sure you want to buy this material for
You're already Subscribed!
Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'