Architectured ceramics with tunable toughness and stiffness

Highlights

• Developing industrially scalable fabrication technique based on laser cutting.

• Revealing novel structure-performance relationships in architectured ceramics.

• Improving multi-hit capability of bio-inspired ceramics by tuning cut depth.

• Enriching cut depth in ceramics to improve dynamic energy absorption performance.

Abstract

Architectured materials/structures provide avenues as a robust design strategy to enhance the strength and toughness of brittle materials. Architectured materials and interfaces can transform brittle ceramics into impact resistant structures with tunable toughness, strength and stiffness. In this work, we have developed a fast, simplified and industrially scalable fabrication technique based on laser machining for large-scale architectured ceramics. Utilizing this technique, a new class of advanced ceramics based on bio-inspired architectures have been designed to improve and tune the mechanical response in multi-impact conditions. The multilayered ceramics were manufactured by stacking laser-cut hexagonal tiles (with differing cut depths) and interlayers made of the commercial monomer Surlyn®. Stereo/3D laser scanning microscopes and nondestructive evaluation (NDE) techniques including infrared thermography, X-ray radiography and X-ray penetrant inspection were used to assess the architectures before and evaluate the multiscale damage after each impact. It was found that the multilayered architectured ceramic systems with a partial-cut depth (i.e., 40% and 70%) exhibited higher dynamic energy absorption performance (up to 220% for the 3rd impact) and higher stiffness (up to 80% for the 3rd impact) than the multilayered plain ceramic. The results showed a bell-shaped response in the partial-cut architectured ceramics, indicating tough materials (opposed to the plain one) and superior multi-hit resistance owing to the energy dissipation mechanisms including plastic deformation in adhesive interlayers and inter-cuts, crack deflection, frictional energy dissipation due to tile sliding (absent toughening mechanisms in the plain system) as well as ceramic fracture upon flexural cracks in the partial-cuts and delamination crack (absent mechanisms in the 100% cut-depth architectured system).

Introduction

Recent implementation of architectured material/structure designs in modern industries is leading to high performing structures [1]. Architectured materials include composites [2], [3], [4] and lattice materials (composed of only a small fraction of solid) [5], [6] have been well studied. In contrast, fully solid architectured materials/structures with two or three dimensional arrangements of building blocks [7], [8], [9], [10] have been investigated to a lesser extent. In this type of the architectured system, stiff building blocks deform little within elastic limits while the weak interfaces between them allow crack formation and lead to nonlinear deformations due to frictional sliding. These building blocks have been fabricated through different techniques such as additive manufacturing [11], casting [12] or laser processing [9] with various shapes (e.g. tetrahedral, octahedral, jigsaw and cubic [13], [14]). The behavior of the building blocks and their interfaces (such as progressive sliding, rotation, separation, crack deflection and interlocking) program architectured material properties [15].

Architectured material designs allow researchers and engineers to achieve uncommon and attractive combinations of mechanical properties through tuning geometry and interfaces. For example, architecture allows the combination of high strength and toughness, which are generally mutually exclusive in conventional engineering materials [16], [17]. It can also improve impact resistance [9] and ballistic performance [18] in glasses or ceramics. In other words, architectured ceramics reveal unique mechanical properties such as high indentation resistance [19], failure resistance [20], fracture toughness [21], yield strength [22] and thermal stability [23]. The architectures of these structures could make them ideal for use in high power transducers [24], high temperature applications [25] and sound absorbers [26]. The architectured ceramics have also been examined for thermal shock behavior [27], damage resistance [23] and flexural stiffness [10].

The inter-building block interactions generate mechanisms that govern the architectured material’s response. Some of these mechanisms are bioinspired. For example: bone, tooth or mollusk shells depend on interactions between material properties and building block positioning (i.e., contact and friction) accompanying the interfaces’ non-linear behavior. This results in robust and unique combinations of strength, stiffness and toughness [7], [9], [15].

Although a few studies have been performed on the architecture design and optimization [28], [29], [30], [31], less attention has been paid to systemic toughness, strength and stiffness tuning. We recently demonstrated that laser engraving can be used to manufacture three-dimensional architectured ceramics with enhanced resistance to out-of-plane quasi-static and impact loads [9]. By employing these bio-inspired architecture principles [9] and utilizing a industrially scalable, efficient laser machining fabrication technique, a new advanced multilayered ceramic system is proposed. Through this precise manufacturing technique, full control over architectures at desired length scales is achievable. We established toughness, strength and stiffness maps as function of a hexagonal laser cut depth to improve the ceramics’ mechanical properties in a multi-impact condition. The multiscale damage after each impact was examined using nondestructive evaluation (NDE) techniques including X-ray radiography, infrared thermography, zinc penetrant with X-ray and stereo/3D laser scanning microscopes.