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Editor's Notes

• #2: MG Everyone introduce themselves Quick
• #3: JM 1 minute Strain gauges convert mechanical quantities into electrical quantities using the Wheatstone Bridge Structural health monitoring – bridges + damage detection
• #4: WY Less than a minute Dimensions Three types: healthy, small hole and large hole Also added two strain gauges so that we could get a more accurate reading of strain from the hole
• #5: QUICK & SIMPLE!! 1.5 minutes WY Static - 9.11 lbs, set up as cantilever , took measurements Dynamic – same cantilever position as static test 1” and 2” deflection & then let the bar oscillate and then return to equilibrium MG Satec – max moment for a two point load case is at the center, therefore we figured that would give us the most accurate reading because that is where the holes were located. Deflected each bar ¼”
• #6: JM 1 minute For our analytical portion of the project, we also modeled the bar in Abaqus ( explain what this is, 3D modeling something? ) Strain shown with encastre case. Length: 30 inches Width: 1.75 inches Height: 0.5 inches Material: A-36 Steel Young’s Modulus: 29*10^6 Poisson Ratio: 0.3 Force to Center: 72 lb. Boundary Condition: Displacement U3 =0 Comparing the strain values the encastre case records strain in the center on large values on the order of 10^-5 while the first case shows strain on the order of 10^-7. The encastre case records higher strain because the first case is allowed to displace in x-y directions.
• #7: Slipping is allowed to occur in x direction and y direction. Therefore, no strain exists at right end. And there is only noticeable strain at one end of the bar. Strain greater at the center and left support. However, what I started to learn from abaqus was that this would not be a simple conclusion. You can’t just stick a strain gauge on a damaged bar and say, now it is bigger. But that may reasoning may not be true. The location of measured strain may not be compatible for both a damaged and undamaged bar.
• #8: 76 billion dollars worth of repair. n
• #10: WY 1 minute (+ a little more) Stress and strain are directly related, therefore the stress ( and strain) are greatest at the fixed end and decrease as you approach the free end SHOULD WE INCLUDE THIS???? Theoretically, Stress = force/area so when you decrease the cross sectional area, you increase the stress. However our data revealed the opposite
• #11: WY 1 minute (+ a little more) As the bar’s damage was increased, so was the damping ratio. This is because as the bar is weakened, it tries harder to dampen the oscillation. Note that dynamic test was useful in detecting quantity BUT NOT location of the damage. Just the different in damping ratio between ½” and ¾” hole Damping ratio for 1” and 2” dynamic test were very similar - this data is correct because it is the same structure with the same damage.
• #12: MG To deflect the bar ¼” it took the ½” diameter holed bar 79lbf and 72lbf for the ¾” bar – therefore displaying weakness. RMS equation to solve for the % change in strain & compared that the % change in load. By comparing these two, not only was it apparent that the strain gauges were more effective in detecting a change in strain in the bar, but also we were able to get a better idea of where the damage might be located – between 2 & 5
• #14: JM For our experiments, the strain around the hole decreased as the damage increased. We believed this was because the strain became more concentrated at the hole – however we could not prove this because we could not place a strain gauge at the hole. For our theoretical model however, we were able to calculate the strain at the hole – which increased as the damage increased – therefore proving our theory. Frequency - the same!!
• #15: MG Based on our testing, we have concluded that despite the many external factors that can affect strain gauges detection of damage , the two major factors are distance from damage and the type and amount of force applied Static & Dynamic test– only resulted in the quantity of strain difference Satec bending test not only determined quantity of change but also gave a rough idea of the location + proved effectiveness of strain gauges Ideal conditions – such as bent in the right direction – right amount of force applied, large enough damage and close enough to damage
• #16: WY
• #17: WY