# An Experimental Strain-Based Study on the Working State of Husk Mortar Wallboards with Openings
## 4 Data Analysis
### Characteristic Curve  
For the seven specimens for which the uniformly distributed strain values are measured, Figure 11a-g draws their characteristic curves of the relationship between \(F_{j}\) and \(E_{j,\text{norm}}\). To be specific, CP stands for the crack point, and FP stands for the failure point, which is defined as the point where the slope of the curve changes greatly. Figure 11 shows that the seven specimens basically embody a similar feature of three working stages, particularly the failure loads dotted in the \(F_{j}-E_{j,\text{norm}}\) curves. Three working stages can be seen in Figure 11, together with the experimental observations:  
In Figure 11a, before the load reaches 55.0 kN, specimen 1-1 works in an elastic state. Afterwards, specimen 1-1 enters an elastic-plastic working state, as the inflection point from a linear shape to a nonlinear shape in the \(F_{j}-E_{j,\text{norm}}\) curve emerges. As the load changes from 55.0 kN to 65.0 kN, specimen 1-1 works in an elastic-plastic state due to the propagation of the first crack and the appearance of other cracks. Notably, however, specimen 1-1 maintains a stable mode of strain energy distribution in these two working states. When the load reaches 65.0 kN, the second inflection point in the \(F_{j}-E_{j,\text{norm}}\) curve emerges, at which point specimen 1-1 cannot maintain a stable mode of strain energy distribution before collapsing. According to the definition in reference [29; 30], defining the first inflection point as the cracking load, and the second inflection point as the failure load, it can be seen from Figure 11a that 55.0 kN is the crack load of specimen 1-1, 65.0 kN is the failure load of specimen 1-1, and 93.2 kN is the ultimate load of specimen 1-1. Similarly, in Figure 11b the crack load, failure load, and ultimate load of specimen 1-2 are 20.5 kN, 69.8 kN, and 78.6 kN, respectively. In Figure 11c the crack load, failure load, and ultimate load of specimen 1-3 are 17.9 kN, 42.0 kN, and 62.3 kN, respectively. In Figure 11d the crack load, failure load, and ultimate load of specimen 1-4 are 18.1 kN, 45.4 kN, and 47.5 kN, respectively. In Figure 11e the crack load, failure load, and ultimate load of specimen 2-2 are 21.5 kN, 74.6 kN, and 81.3 kN,respectively. In Figure 11f the crack load, failure load, and ultimate load of specimen 2-3 are 21.3 kN, 42.5 kN, and 47.6 kN, respectively. In Figure 11g the crack load, failure load, and ultimate load of specimen 2-4 are 27.5 kN, 36.6 kN, and 42.0 kN, respectively. Here, three points must be emphasized: (1) FP exists in the \(F_{j}-E_{j,\text{norm}}\) curve of every specimen, as shown in Figure 11. (2) FP emerges in the elastic-plastic working stage of the specimen. (3) The working states of the wallboard are different before and after the appearance of FP. The former  
Figure 11: The \(F_{j}-E_{j,\text{norm}}\) curves of the specimens. Note: CP is the cracking load point; FP is the failure load point. state is relatively stable and maintains a relatively constant mode/pattern, while the latter state is unstable/changeable with the load increment. Therefore, based on the characteristic point in the \(F_{j}-E_{j,\text{norm}}\) curve, the response of a wallboard to a load increment can be divided into two working states: the stable/normal working state occurring until the characteristic point and the unstable/failure working state from the characteristic point to the collapse of the wallboard. The failure load is defined as the load value at the characteristic point. The results of the crack load and failure load derived from the strain data are consistent with the results based on observations, as shown in Figure 12. Actually, the crack results based on observation requires manpower and depends on the experimental environment. Therefore, the crack load cannot be defined clearly in this way. Moreover, when the crack occurs in the initial stage, the width of the crack is not large enough for observation. With strain analysis method, the initial stage of crack could be captured reasonably.