Fig. 4.

Photosynthesis-assisted strengthening regulated by preloads. (A) Schematics to illustrate the photosynthesis-assisted strengthening in experimental samples without and with a prestretch. (B) Stress–strain curves of three samples: with a prestretch of 1.3 after 4-h light illumination and 4-h darkness, without a prestretch after 4-h light illumination and 4-h darkness, and without a prestretch after 8-h darkness. (C) FTIR spectra corresponding to the above three processed samples. (D) Young’s moduli and tensile strengths of the processed samples with various prestretches. Error bars represent SDs of 3–5 samples. (E) Schematics to illustrate the photosynthesis process on a sample plate under nonuniform prestresses applied by a 3D-printed foot. (F) Young’s modulus distribution of the processed sample plate. (G) The master curve between the applied compressive prestrain and the resultant Young’s modulus of the sample after the photosynthesis process (4-h illumination and 4-h darkness). Error bars represent SDs of 3–5 samples. (H) The compressive prestrain distribution translated from the Young’s modulus distribution in (F).