# Static Compressive Properties of Polypropylene Fiber Foam Concrete with Concave Hexagonal Unit Cell
## 3 Results and Discussion
### Deformability Analysis  
The digital scattering method (DSCM) was used to compare the digital images before and after the deformation of the observation surface of the concave hexagonal unit cell, as well as to analyze and obtain the deformation information of the observation surface of the object. This was conducted by matching the calculated sub-regions before and after the deformation, based on the correlation search calculation of the gray value distribution characteristics. The displacement field was determined by measuring the displacement components u and v of the sample points (x\({}_{0}\), y\({}_{0}\)) on the surface of the concave hexagonal cell in an axial two-dimensional way, and the lateral displacement nephogram of the concave hexagonal cell during static compression was obtained. In this experiment, the deformation when the specimen was damaged was taken as the equivalent deformation, and the displacement nephogram of concave hexagonal cells with different fiber contents under peak stress was made, as shown in Figure 4.  
Figure 4 shows that during the deformation of the concave hexagonal unit cells with different fiber contents, the displacement at the middle of the concave part on both sides of the cell wall is the largest, and its displacement direction is inside the concave hexagonal  
Figure 4: Cloud diagram of lateral displacement of the concave hexagonal unit cell: (**a**) A-0; (**b**) A-0.5; (**c**) A-1.0; (**d**) A-1.5; (**e**) A-2.0; (**f**) A-2.5. unit cell. With the increase in fiber content, the displacement change demarcation line appears more and more obvious at the side of the cell wall, as shown in Figure 4d-f. The displacement of the material changes sharply at this place, which indicates that the foam concrete material has a larger deformation at this place before the structural damage of the concave hexagonal unit cells. Compared with the two sides of the cell wall, the transverse displacement changes below and above the cell wall are smaller, and by comparing the displacement distribution at the two ends of the cell wall, the displacement at the left end is smaller than the displacement at the right end, which indicates that the tensile deformation occurs both below and above during the compression process. Therefore, the deformation pattern of the concave hexagonal unit cells during static compression is as follows: the upper and lower part of the cell wall stretches outward, while the concave parts on the left and right sides bend and deform under pressure, and the middle part shrinks inward. The width of the transverse displacement interval is the maximum difference of transverse displacement of the material, which can visually reflect the ability of transverse deformation of the material. According to the transverse displacement cloud diagram of the concave hexagonal unit cells, the transverse displacement interval width of the samples were compared. The transverse displacement interval width of the sample with 0% fiber content was 0.135 mm, while the transverse displacement interval values of the other five groups of concave hexagonal unit cells were 0.140 mm, 0.172 mm, 0.181 mm, 0.162 mm, and 0.152 mm in order, which proves that the variation of the content of polypropylene fibers can affect the transverse deformation ability of the concave hexagonal unit cell. In Figure 4d, it can be observed that the transverse displacement variation of the concave hexagonal unit cells with 1.5% fiber content was greater than that with other fiber contents, and the width of its transverse displacement interval increased by 34.1% compared with that of the concave hexagonal unit cells with 0% fiber content. Poisson's ratio is an elastic constant reflecting the transverse deformation of materials. Since the sample structure used in this test was the concave hexagonal cell, sampling points were set in the concave portions of both sides of the cell wall to obtain the variation of the transverse distance between points.