Flexible phone screens are being tested for their stress properties by scientists

Researchers presented an analysis of the mechanical characteristics of flexible screens in an article that was recently published in the open-access journal Materials.

Organic light-emitting devices (OLEDs) have become increasingly important in a variety of industries, including smart clothing, flexible displays, and other applications in recent years. As OLEDs become more widely used in display goods, the structural stability and optimization of flexible OLED display module screens have emerged as important criteria for addressing the concerns of portability and economics that have arisen.

With a tight bend radius, the gadget is put under excessive stress during the bending operation, leading to it ripping off and causing irreparable damage to the screen and other components. The finite element method can be used to determine the mechanism of damage and peeling of the adhesive layer of a flexible OLED display module screen, and small OLED screen can also be used to obtain stress and strain results for the screen.

A novel hole-transport layer for the host material was created using a novel technology (the ball milling process) and a green halogen-free solvent. This layer not only improved the photoelectric response of the optical monomer-based thin-film device, but it also exhibited good stability under continuous stress, as demonstrated in this study. There is, however, a chasm between the stacking structure and the actual flexible screen module in this arrangement.

Model of the geometric structure of the U-shaped bending mode. The left reference point remained fixed, and the bending was accomplished by moving the fixture board from position A to position B within the bending time t seconds during which the bending was completed. Considering that the bending radius was R and the bending angle was, the lateral gap was equal to R. Image courtesy of Niu, L. et al., Materials Science and Engineering.

Concerning the Research
The authors of this study used finite element analysis to develop a bending model for a flexible screen, which they then demonstrated. In order to estimate the growth of Mises stress as the bending radius decreased for common U-shaped bending as well as the redistribution of the tensile and compression zones, an imaging experiment was performed. In order to reduce the likelihood of structural collapse, a bending mode in the shape of a water drop was also investigated.

In order to create the real stacking model for the flexible screen module, the team utilized the finite element software ABAQUS. A discussion was held on the mechanical behavior of small OLED display display module flexible screens, as well as OCA thickness-shape, impact of bending radius on mechanical behavior, and bending mode (which included water drop shape and U-shaped). An imaging experiment was carried out in order to confirm the findings of the analysis.

The mechanical behavior of the flexible screen was simulated by the researchers using a finite element model created using the ABAQUS software. A fixture board and a screen module were cemented together, and the movement of the fixture board drove the bending of the screen. The flexible screen module was constructed from a series of multi-layered films with varying mechanical properties. Because of the way OCA bonded the layers of film together and coordinated the deformation of each layer during the folding process, it was critical for maintaining the structural integrity of the flexible screen module. For a 180-degree folding simulation, the bending radii were set to 3 mm, 2.5 mm, 2 mm, 1.5 mm, and 1 mm, with a bending time of t = 18 s. The bending radii were set to 3 mm, 2.5 mm, 2 mm, 1.5 mm, and 1 mm, respectively.

Observations are made.
According to the results of the analysis, bending with a short bending radius would not only be effective, but it would also reduce the likelihood of the structure failing. The discrepancy ratio between the experimental and simulated ranges for the same bending radius was less than 1%, indicating that both the finite element model and the experimental data were accurate.

When the bending radius was R = 2 mm, the spherical droplet had a radius of 2.286 mm and the bending radius was R = 2 mm. With a maximum increase ratio of 13.07% and a maximum increment ratio of 18.56%, S1/S5 had the highest absolute strain increment ratios, while S2/S5 had the lowest absolute strain increment ratios. S1/S5 had the highest absolute strain increment ratios, with absolute strain increment ratios of 1.0053% and 1.0042%, respectively.

In terms of effects on the small OLED screen light-emitting layer, the profiles S3, S4, and S5 all had similar results, with the highest difference ratios of 1.27% and 3.61% for S3/S5 and S4/S5 being the most significant. When compared to S5, the maximum stress on the  display module layer was increased by 13.53% and 24.04%, respectively, when using the S1 and S2 profiles. When the bending radius was 2.5 mm, the plastic strain started on the inside of the CPI layer, in the squeezed area, and progressed to the outside of the layer. It wasn't until the bending radius reached 2 millimeters that the outside tension area experienced plastic strain. When the bending radius was 1.5 mm, the plastic strain occurred at the outer tension area of the bending radius.

When R = 2.5 mm was used, the maximum tensile stress was reduced by 23.99%, but the maximum compressive stress was raised by 15.82%, resulting in a net reduction of 23.99%. By increasing R by 3 mm, the maximum compressive stress was increased by 20.22%, while the maximum tensile stress was decreased by 27.54%.

Concluding Remarks
After all is said and done, this study has helped to clarify the bending model for flexible screens by utilizing finite element analysis. Using the commonly used U-shaped bending, it was discovered that the maximum Mises stress increases rapidly as the bending radius is decreased. The small screen and BP layer stack sequences, as well as the single layer with the highest toxicity and the profiles of the OCA layer, were all optimized for performance.

In accordance with the optimization, the layer material selection was dictated by redistribution of the tensile and compression zones within the structure. In order to validate the results of the analysis, an imaging experiment was performed to determine the maximum slip distance during bending.