## 3 Experimental Results
### Results of Dynamic Uniaxial Compression Tests on Hard Ice
#### 3.1.3 Dynamic Deformation Measurement by DSCM
Some parts may still closely connect to a main bearing ice column, while some parts may not. If the part that contains certain speckle surface region connects to a main bearing ice column, this speckle surface region may deform with the bearing ice column together. On the other hand, if that part does not connect to a main bearing ice column, this speckle surface region may not deform further, or even deform reversely when the surrounding constraint is not sufficient. That is to say, at a moment ago, a reference point moves downward, while at a moment in the future it may move upward owning to separation from the main bearing column of ice sample. This scenario is similar to that a spring restores to its original length after the applied force is removed. In a word, when sample has not been damaged or have been just slightly damaged, the local strains derived from the pixel placements of the speckle surface can represent deformation of the exterior and interior of sample; While, when sample has been damaged by cracks, the local strains can still represent deformation of sample surface, but they might not represent deformation of the interior of sample again. Thus, at moment C, regions with small strain values should have separated from the main bearing column. While regions with large compression strain values should still connect to the main bearing column, so the reference points attached on these regions can continue shortening the distances between each other. At this moment, the local strains of the speckle surface cannot represent the deformation of the interior of sample again, and perhaps cause an illusion that the sample has not been in compression state again, but the sample is actually under compression state. At moment D, load decreases to a low level, the whole speckle surface is in compression state according to the strain contour shown in Figure 12(a4). The strain field is severally uneven. The upper section is compressed severally, with maximum strain value up to 5.0\(\%\), while the lower section is compressed slightly, with minimum strain value even close to zero. The non-uniform appearance in strain field feature can also be explained in the way that we have done at moment C. With regard to strains in the x-direction at four different moments, they are all tension strain. At moments A and B, strain values are both smaller than 0.4\(\%\) (as shown in Figure 12(b1,b2)), indicating only a slight expansion exists in the horizontal direction. When ice is compressed further, obvious expansion is found. At moment C, an obvious region in which strain values in the \(x\)-direction are higher than 10\(\%\) appears (as shown in Figure 12(b3)), indicating a vertical crack has formed within this region and this is consistent with crack observation by naked-eye. At moment D, the strain values in most of the surface regions are greater than 10\(\%\), and a value of 97\(\%\) is obtained in the vertical middle region (as shown in Figure 12(b4)). This appearance indicates ice sample has expanded considerably in the horizontal direction, consistent with the fact that at this moment ice has been severally destroyed by cracks (as shown in Figure 9(a5,c5)). Figure 11: Lattice of reference points (the number of reference points is 1804; the spacing between the adjacent reference points is 3 pixels; the reference subzone is a square of 21 pixels in each edge, and the object subzone is four times the size of reference subzone). Figure 10: Stress versus nominal strain profile of sample HH05 mps2 at \(-10\)\({}^{\circ}\)C (A, B, C, and D denote specific moments, corresponding to time point 0, 0.38, 0.85 and 1.26 ms, respectively). Strain field derived from pixel displacement field can be used to estimate whether the sample deformation in the compression test is uniform.