Optical residual stress analysis

ReSA system based on 3D-Micro-DIC stereo sensor for residual stress analysis

Strain dis­tri­bu­ti­on εxx (hori­zon­tal) at three dril­ling depths of 0.2mm (left), 0.4mm (cent­re) and after 1mm (right); FoV: 8,4mm x 7mm; Dril­ling dia­me­ter: 1,8mm; Arrows: direc­tion of princi­pal strain ε2.

 

The hole dril­ling method in com­bi­na­ti­on with strain gau­ges is an estab­lis­hed method for resi­du­al stress ana­ly­sis in metal mate­ri­als. In con­trast a full-field and non-con­ta­ct mea­su­re­ment using VIC-3D is espe­cial­ly advan­ta­ge­ous in order to quan­ti­fy the non-homo­ge­ne­ous resi­du­al strains and stres­ses wit­hin com­po­si­te struc­tures. The examp­le abo­ve shows the strain mea­su­re­ment εxx of a car­bon com­po­si­te at dif­fe­rent dril­ling depths. The right image is super­po­sed with an FEM model of a quar­ter sec­tion. isi-sys offers a turn-key solu­ti­on for resi­du­al stress ana­ly­sis accord­ing to the hole dril­ling method in com­bi­na­ti­on with a spe­cial ver­si­on of the 3D Micro DIC ste­reo sen­sor.

 

 

 

The images below show the defor­ma­ti­ons (U, V, W) of the car­bon fib­re com­po­si­te at 1mm dril­ling depth cor­re­spon­ding to the strain mea­su­re­ment abo­ve. The examp­les show the mea­su­red defor­ma­ti­on and strain clo­se to the dril­led hole with high spa­ti­al reso­lu­ti­on, even at very small dia­me­ters (2.3mm down to 0.8mm). This is pos­si­ble as the ste­reo sen­sor set-up is desi­gned for a FOV of about 8.4mm x 7mm @ 5Mpx. This is hard­ly resolva­ble using the strain gau­ge princip­le. The resi­du­al strain ana­ly­sis sys­tem is equip­ped with a spe­cial drill, ope­ra­ting with around 100.000 to 300.000 RPM. The spe­cial ver­si­on of the 3D Micro DIC sen­sor allows to drill and mea­su­re without repo­si­tio­ning of the drill or the sensor.

 

 

ReSA — the new Residual Strain/Stress Analysis solution

Defor­ma­ti­ons (U, V, W) at 1mm dril­ling depth wit­hin car­bon com­po­si­te mea­su­red by the Strai­no­gra­phy sen­sor; FoV 8,4 mm x 7mm; Dril­ling diam­ter 1,8mm; Arrows: direc­tion of the princi­pal strain ε2.

 

ReSA system advantages against strain gauge based methods

 

Strain gau­ge and hole dril­ling method ReSA sys­tem based on 3D-Micro-DIC
Mea­su­re­ment errors:
- Errors due to misa­lign­ment of the dril­led hole against the cent­re of the strain gau­ge rosette + No requi­re­ment on the exact dril­ling hole posi­ti­on rela­ti­ve to the sen­sor, no cor­re­spon­ding errors
- Fib­re matrix direc­tion and strain gau­ge align­ment requi­red or rela­ti­ve direc­tion need be known + No adjus­t­ment bet­ween sen­sor and the mate­ri­al matrix direc­tions is requi­red or needs to be know
- Errors due to indi­vi­du­al strain gau­ge application + Repeat­a­ble pre­pa­ra­ti­on of the area of interest
Tech­ni­cal consideration:
- Sin­gle point mea­su­re­ment of strain, aver­aging across the effec­ti­ve strain gau­ge area + Full field strain and defor­ma­ti­on mea­su­re­ment, high spa­ti­al reso­lu­ti­on clo­se to the hole
- Results depen­ding on the app­lied eva­lua­ti­on model + Reli­able post-pro­ces­sing with Vic-3DTM
- Sin­gle point values of resi­du­al stres­ses only – so not repre­sen­ta­ti­ve for inho­mo­ge­ne­ous material + Full field resi­du­al stress data sui­ta­ble for inho­mo­ge­ne­ous materials
Eco­no­mi­c­al aspects:
- High cost per mea­su­re­ment due to strain gauge + Low ope­ra­ti­on cost per measurement
- Pre­pa­ra­ti­on time for app­ly­ing the strain gauge + Fast and simp­le pre­pa­ra­ti­on of object surface