# Development and Assessment of a 4D Printing Technique for Space Applications
## 3 Results  
### Programming Device  
In the pursuit of enhancing the 4D printing process for SMP hinges, a programming device was meticulously developed through an iterative design approach. The overarching goal was to facilitate the effective programming of SMP hinges for subsequent deployment in space applications. The design process commenced with preliminary tests utilizing PLA, and the final version of the programming device was materialized using PEEK. This section focuses on two distinct versions of the programming device, elucidating the evolution between them. Later, we explore the impact of the two versions on improving the 4D printing process. **Shared Features:**  
Both iterations of the programming device share fundamental features essential to their functionality. * **Dual Handles:** Each version incorporates two handles--a larger one referred to as the base handle and a smaller rotating handle. These handles are interconnected through a press fit along the \(y\)-\(y\) axis, achieved by embedding an M3 thread insert into connecting holes. For hinge programming, these two handles are pulled towards each other, allowing the hinge inside to be folded. * **Vertical Alignment Feature:** Positioned at the end of the base handle, this feature prevents over-tightening when the device is secured in a vice for cooling. Conversely, the rotating handle features a negative counterpart of this alignment feature. **First Version:**  
The initial iteration of the programming device (version 1) adopts a flexible design for hinge fixation, allowing for quick insertion and removal. Key features of the first version include teeth and slidable hold-down mechanism. The rotating handle incorporates small teeth to secure hinges, while the base handle features a slidable hold-down mechanism aiding in \(z\)-direction stability (refer to Figure 4). Programming Steps (version 1):  
1. Slide back the slidable hold-down mechanism on the base handle. 2. Load the hinge into the programming device, ensuring the teeth grip the hinge. 3. Slide the hold-down mechanism back above the hinge, securing it on the base handle side (shown in Figure 5a). 4. Place the device with the loaded hinge in the build chamber of Orion's A150 and heat (see Figure 5b). 5. Quickly remove the device from the 3D printer. 6. Pull both handles towards each other, effectively folding the hinge, while at the same time sliding back the hold-down mechanism on the base handle side. exposed, to that heat. The different line colors visualize the temperature \(T_{\text{set}}\) that was entered on the printer's interface. First, we can see that the entered temperature was almost never consistently accomplished, but instead the surface temperature only lay within a range of the entered temperature. Depending on the heating time, the measured surface temperature was sometimes below the entered temperature, but in some cases it was even above the entered temperature. Next, we investigated how well the hinges could be programmed at their measured surface temperature, for that, Figure 8 provides valuable insight.On the \(x\) axis of Figure 8 we can see the recorded surface temperature \(T_{\text{S}}\) and on the \(y\) axis the fixity ratio calculated using Equation (1) is shown. The two colors show whether a data point belongs to the experiment conducted with the first iteration programming device (blue) or the second iteration (orange). In addition to the raw data points, a linear regression was used to visualize possible trends in the data set, which is displayed as a line in Figure 8. The colored area around the lines represents the 95% confidence interval. Of course, the linear regression line can only sensibly be interpreted in the range of the 0%... 100% fixity ratio; therefore the data above 100% were cut off. What we can clearly see in Figure 8 is that the higher surface temperatures were highly correlative with high fixity ratios. This data also held statistical significance with \(p_{\text{v1}}=1.6\cdot 10^{-5}\) and \(p_{\text{v2}}=3.3\cdot 10^{-5}\).