Dynamic Compression of Metals

Dynamic compression

Stu­dy­ing the beha­vi­or of metals during a high-speed dyna­mic com­pres­si­on event has always been chal­len­ging due to the com­plex test set up and fast data cap­tu­re rates requi­red. Cur­r­ent­ly, very litt­le lite­ra­tu­re is avail­ab­le regar­ding defor­ma­ti­on beha­vi­or at strain rates of  10 to 500s-1. Uti­li­zing high-speed came­ras, the Vic-3D HS sys­tem can be used to quan­ti­fy the sur­face dis­pla­ce­ments and strains in three dimen­si­ons over the ent­i­re field with gre­at pre­cisi­on. Digi­tal Image Cor­re­la­ti­on (DIC) has gai­ned widespread popu­la­ri­ty over recent years in such high-speed app­li­ca­ti­ons due to its high accu­ra­cy, fle­xi­bi­li­ty and ease of use.

 

 

 

Dynamic compression2In this examp­le, a 6mm dia­me­ter cylind­ri­cal spe­ci­men was com­pres­sed at a strain rate of 50s-1. The Vic-3D HS sys­tem was used to cap­tu­re the  sur­face dis­pla­ce­ments and  strains on  the  spe­ci­men during the event. A ran­dom speck­le pat­tern is app­lied to the spe­ci­men that allows the ana­ly­sis soft­ware to easi­ly track the defor­ma­ti­on to sub-pixel accu­ra­cy. Alt­hough the high- speed came­ras are capa­ble of much hig­her cap­tu­re rates, for this test they were set to an appro­pria­te frame rate of 14,400fps to maxi­mi­ze spa­ti­al reso­lu­ti­on while acqui­ring an ade­qua­te num­ber of images during the event. The came­ras were post-trig­ger at a reso­lu­ti­on of 1024 x 400 pixels. After the event, the images are trans­fer­red to the computer’s  hard  dri­ve, and  then  post-pro­ces­sed using Vic-3D ana­ly­sis software.

Images cour­te­sy of Amos Gilat & Jere­my Seidt at Ohio Sta­te University.

 

 

Contractions of a Muscle

Bio­me­cha­nic rese­ar­chers were stu­dy­ing the con­trac­tions of a rat Tibia­lis Ante­rior mus­cle.  It was desi­ra­ble to quick­ly and accu­rate­ly quan­ti­fy the over­all move­ments, as well as loca­li­zed variations.

Challenges

Becau­se the expe­ri­ments invol­ved live tis­su­es, con­ven­tio­nal gau­ges were dif­fi­cult to app­ly and ten­ded to inter­fe­re with the moti­on under stu­dy.  It was important to cap­tu­re data quick­ly, and for as many points as pos­si­ble.  Mar­ker tracking had been used, but pro­vi­ded only gross aver­a­ges.  It was also time-con­suming and tedious for the rese­ar­chers to pro­cess this type of  information.

Solution

The Vic-3D sys­tem was used to rapidly cap­tu­re con­trac­tion data over the ent­i­re mus­cle sur­face.  Due to the system’s speed and sim­pli­ci­ty, it was pos­si­ble to make nume­rous mea­su­re­ments at pre­cise­ly timed inter­vals.  The­re was no inter­ac­tion with the spe­ci­men, and no need to guess which are­as would be of grea­test interest.

The resul­ting mea­su­re­ments pro­vi­ded high spa­ti­al reso­lu­ti­on and made it pos­si­ble to iden­ti­fy nume­rous are­as whe­re “bun­ching” of the mus­cle tis­sue cau­sed signi­fi­cant varia­ti­ons in mus­cle con­trac­tion.  The­se are­as had not been pre­vious­ly iden­ti­fied with con­ven­tio­nal methods.  Final­ly, all cal­cu­la­ti­ons were done auto­ma­ti­cal­ly.  This saved con­si­derable time and avoided the pos­si­bi­li­ty of human error in the data processing.

 

Deformation Measurement

Aerospace Application Example

aerospace_1_notitle-300x247Air­bus has built a repu­ta­ti­on for inno­va­ti­ve air­craft, reco­gni­zed around  the world for their safe­ty and effi­ci­en­cy. All of the­se attri­bu­tes are dri­ven by a top-notch tes­ting pro­gram, who­se inno­va­ti­ve prac­ti­ce are evi­den­ced by their use of the Vic-3D mea­su­re­ment system.

One of the goals of the Air­bus tes­ting pro­gram is to cha­rac­te­ri­ze the struc­tu­ral dama­ge cau­sed by col­li­si­ons bet­ween the air­craft and small pro­jec­ti­les such as birds and other ground based debris, and to ensu­re that the struc­tu­ral inte­gri­ty of the air­craft is maintained.

This type of event can be repro­du­ced by firing a varie­ty of dif­fe­rent types of pro­jec­ti­le at a pie­ce of air­craft struc­tu­re at a high velo­ci­ty. The results obtai­ned can be used to com­pa­re with com­pu­ter models of the struc­tu­re under impact loads, lea­ding to more high­ly opti­mi­zed and safer designs.

 

aerospace_2_notitle-300x224Dr. Richard Bur­gue­te, expe­ri­men­tal mecha­nics spe­cia­list at Air­bus UK sin­ce 1997, exp­lains the bene­fits of this approach as fol­lows: “The VIC-3D sys­tem allows us to be sure we have cap­tu­red all of the rele­vant data, some of which might have other­wi­se been unobtainable.”

Vibration Analysis of a Brake Disc

Bremsen1 Bremsen2
 x
Auto­mo­bi­les are sub­ject to many for­ces using ope­ra­ti­on. Vibra­ti­ons from the engi­ne or the road-sur­face trans­mit through the vehicle’s chas­sis and sus­pen­si­on to the most essen­ti­al mecha­ni­cal com­po­nent of the vehi­cle, the bra­ke system.

Bremsen3

In this examp­le, a 14” dia­me­ter bra­ke disc from a hea­vy­du­ty truck was exci­ted using a small ham­mer to mea­su­re the vibra­ti­on shapes of the rotor. The three-dimen­sio­nal ope­ra­tio­nal deflec­tion shapes were easi­ly iden­ti­fied and mea­su­red using the Vic-3D™ HS Vibra­ti­on Ana­ly­sis Sys­tem. Ampli­tu­des as small as 40 nano­me­ters were mea­su­red at a fre­quen­cy of appro­xi­mate­ly 2,000 Hz.

 

Strain Measurement on a Gearwheel

Challenges

Assem­bled com­pon­ents typi­cal­ly have com­plex inter­ac­tions with one ano­t­her. Con­ta­ct points can vary during ope­ra­tio­nal cycles due to part move­ment. This means that the loca­ti­ons of peak strains can be hard to pre­dict, and they are often not sta­tio­na­ry. The move­ment of parts can also make it imp­rac­ti­cal to main­tain electri­cal con­nec­tions with gau­ges. Even when they are sta­tio­na­ry and easy to loca­te, the hig­hest strains can be con­cen­tra­ted in very small are­as or have high gra­di­ents. Peak values may be lost to the aver­aging effect pro­du­ced by gauges.

 

Solution

Vic-3D pro­vi­ded a means for making strain mea­su­re­ments across the ent­i­re pro­fi­le of the gear tooth. Becau­se it pro­vi­des full-field mea­su­re­ments, it was not necessa­ry to choo­se a par­ti­cu­lar point at which mea­su­re­ments would be made. This allo­wed the peak strains to be clear­ly visua­li­zed and accu­rate­ly mea­su­red at various sta­ges of the ope­ra­tio­nal cycle. Vic-3D also mea­su­red dis­pla­ce­ment in three dimen­si­ons. This fea­ture allo­wed our cus­to­mer to reco­gni­ze and quan­ti­fy twis­ting of the gear tooth under load.

Exhaust pipe

Exhaust1The engi­neers at Cum­mins design and test their engi­nes to with­stand real-world con­di­ti­ons, ran­ging from mili­ta­ry deploy­ments to hea­vy-duty indus­tri­al sites. Cum­mins engi­neers want to know exact­ly how their parts are deforming under the com­bi­na­ti­on of ther­mal and mecha­ni­cal loads. This means they’ve got to per­form their tests with the engi­nes run­ning – and hot.

Becau­se of the com­plex strain fiel­ds pro­du­ced under the­se con­di­ti­ons, con­ven­tio­nal gau­ges can­not satisfy Cum­mins’ requi­re­ments. FEA simu­la­ti­ons are also limi­ted, due to the uncer­tain bounda­ry con­di­ti­ons. With the Vic-3D sys­tem, Cum­mins engi­neers are able to obtain detail­ed three-dimen­sio­nal strain mea­su­re­ments. The­se mea­su­re­ments are made under real loading con­di­ti­ons while the engi­ne is run­ning. In addi­ti­on, the Vic-3D sys­tem is easy to set up and can mea­su­re both small parts and lar­ge assemblies.

 

 .….….….….….….….….….….….….….….….….….….….….….…..

exhaust2

Paul Glo­eck­ner, seni­or rese­arch engi­neer at Cum­mins, exp­lains the use­ful­ness of the Vic-3D sys­tem as fol­lows: “This tool allows us to make mea­su­re­ments that were pre­vious­ly not pos­si­ble. It has also allo­wed us to con­si­der­ab­ly redu­ce the time requi­red for the­se tests.”

Microscopic Strain Measurement

Combination of a special stereomicroscope with Vic-3D digital image correlation on electronic components.

 

Uni Wien Mikroskop

Mea­su­re­ment set up: Ste­reo micro­scope mounted

on x‑y-z-micro­ta­ble (backside) and ten­si­le machi­ne (right).

 

Uni Wien Mikroskop2

Uni Wien Mikroskop3

Ser­ve­r­ed cer­a­mic capa­ci­tor chip under ben­ding load (image width approx. 4mm):
Strain in x‑direction (upper image) and y- direc­tion (lower image).

 

Uni Wien Mikroskop4

Uni Wien Mikroskop5

Stan­dard deri­va­ti­on (upper) under load : An incre­a­sed value occurs on the midd­le against the reference
sta­te by the local­ly small bul­ge at the con­ta­ct bet­ween chip and board (see 3D con­ture below). This might be caused
by mate­ri­al , which is pres­sed tog­e­ther bet­ween the two parts (inclu­ding the colour lay­er). In the upper area the
incre­a­sed values of the stan­dard deri­va­ti­on is cau­sed by the redu­ced speck­le density.