Extremal Structures with Embedded Pre-Failure Indicators

Abstract

Preemptive identification of potential failure under loading of engineering structures is a critical challenge. Our study presents an innovative approach to built-in pre-failure indicators within multiscale structural designs utilizing the design freedom of topology optimization. The indicators are engineered to visibly signal load conditions approaching the global critical buckling load. By showing non-critical local buckling when activated, the indicators provide early warning without compromising the overall structural integrity of the design. This proactive safety feature enhances design reliability. With multiscale analysis, macroscale stresses are related to microscale buckling stability. This relationship is applied through tailored stress constraints to prevent local buckling in general while deliberately triggering it at predefined locations under specific load conditions. Experimental testing of 3D-printed designs confirms a strong correlation with numerical simulations. This not only demonstrates the feasibility of creating structures that can signal the need for load reduction or maintenance but also significantly narrows the gap between theoretical optimization models and their practical application. This research contributes to the design of safer structures by introducing built-in early-warning failure systems.

Figures (3)

• Figure 1: Structural optimization with embedded pre-failure indicator using homogenized isotropic multiscale material. (A) Stiffness and stability data relative to local volume fractions are obtained through homogenization. (B) The optimization is performed on a coarse mesh using the homogenized material properties to enhance computational efficiency. (C) An optimized homogenized design is obtained with the desired buckling response. (D) The optimized design is de-homogenized to extract a high-resolution physical design. (E) The de-homogenized design is post-evaluated numerically. (F) The de-homogenized design is fabricated for experimental validation of the method.
• Figure 2: Optimized designs without the pre-failure indicator. (A) Numerical and printed BVS designs optimized for maximizing global buckling (The picture of the printed structure is taken with UV light to enhance contrast). The design is sensitive to local buckling, even from residual stresses resulting from the printing process, as seen in the unloaded printed sample. I--II shows the numerical and experimental displacements for the BVS design at 70% stiffness. III shows the local buckling at the maximum experimental displacement of the BVS design. The color bar represents the 2D in-plane von Mises stress (arbitrary units). (B) BVSL structure optimized for maximizing global buckling while preventing local buckling of the microstructure. The picture is taken after the experiment, hence the fracture in the bottom part of the structure. IV--VI shows the displacements of numerical and experimental analysis for the BVSL design. The color bar in IV represents the 2D out-of-plane von Mises stress (arbitrary units). (C) Load/displacement response for numerical and experimental tests with failure points indicated by circles at I, II, IV and V. Vertical dotted lines indicate the critical displacements estimated by the homogenized analysis.
• Figure 3: The two optimized designs with embedded pre-failure indication. (A) Numerical and printed BVSLI designs optimized for maximizing global buckling while embedding a pre-failure indicator. I--IV presents the related buckling modes with the color bar showing the 2D in-plane von Mises stress (arbitrary units). (B) BVSLID structure optimized for maximizing global buckling while accounting for local buckling of the indicator. (C) Load/displacement response for the numerical and experimental tests with an indication of indicator activation and failure points by circles.