1 Introduction
Shell-infill structures generally comprise exterior solid shells and interior porous infill structures, whose closed features can generate superior mechanical performance, such as high stiffness-to-weight ratio, strength-to-weight ratio, energy and sound absorption capacities [
1‐
3]. Compared with conventional pure solid structures, shell-infill structures can concurrently coordinate the design of the overall structure and interior infill configuration with greater design freedom, thereby maximizing the mechanical performance and improving the light weight [
4‐
6].
For shell-infill structures, many studies have focused on the infill configuration and investigated the effects of topology and geometric size on the structural mechanical properties. Li [
7] designed a honeycomb aluminum cell with different unit lengths to investigate the influence of the relative position on the energy absorption capacity. Zhang [
8] compared the crushing performance of shell structures with triangular, hexagonal, and negative Poisson’s ratio (NPR) structures as porous infills; a huge difference was found in terms of energy absorption under both quasi-static compression and impact conditions. Zeng et al. [
9,
10] discussed the differences in the failure modes of shell-infill structures by changing the corrugation angle during compression and three-point bending experiments. Muchhala et al. [
11] investigated the axial compressive deformation mechanism of cenosphere-reinforced closed-cell hybrid aluminum foams at different strain rates. Vengatachalam et al. [
12] studied the initial yield response of closed-cell aluminum foams under both uniaxial and biaxial loadings. Cherniaev [
13] analyzed the damage to sandwich panels with open-cell foam under impact to confirm the protective function of this type of structure. These types of shell structures with porous infills have been widely studied in terms of their compressive performance. Hu et al. [
14] investigated the deformation, strength, and failure modes of woven textile sandwich composites (WTSCs). In addition to the infill configuration, Wang et al. [
15,
16] also explored the buckling deformation mode of cylindrical shells under axial loads through experiments and numerical methods. Most structures mentioned above were fabricated by conventional manufacturing processes, such as stretching from honeycomb structures or casting for shell foam structures.
With the recent utilization of additive manufacturing (AM), structures with complicated geometries, such as shell-infill structures, can be manufactured, providing greater design freedom [
17‐
19]. As a promising infill porous structure, the lattice structure can achieve superior mechanical or multifunctional properties while maintaining an extremely light weight [
20]. Maconachie et al. [
21] reviewed and summarized existing studies on lattice structures and provided design guidance for developing controllable mechanical properties. Body center cubic (BCC) structures are the most widely studied lattice type in terms of their mechanical response and elastoplastic deformation mechanism under quasi-static compression. Peng et al. [
22] numerically analyzed the mapping relationship between the relative density and mechanical properties of four lattice structures, including the BCC structure. Li [
23] investigated the tensile and compressive local stress distributions of stainless-steel BCC unit cells from a microscopic perspective. Smith et al. [
24] also reported the same progressive failure mode of BCC structures under quasistatic compression and blast loading conditions. Merkt et al. [
25] performed compression tests and found that lattices manufactured with titanium alloys demonstrated inferior energy absorption capacity compared to that of stainless steel. To control the deformation behavior, Maskery et al. [
26] realized a gradient-density lattice along the loading direction to obtain progressive layer collapse while ensuring the same energy absorption capacity. Sufiiarov et al. [
27] eliminated shear failure with a computationally generated variable density to strengthen the mechanical responses of lattice structures. Apart from the above mechanism-based design methods, topology optimization can also be used to design cellular patterns or configurations based on the design requirements. Xu et al. [
28] employed topology optimization to obtain the material distribution for an improved BCC structure. Kang et al. [
29] combined topology optimization and a multilattice structure construction strategy to design sandwich-structured cores.
Most of the abovementioned studies related to the BCC lattice have focused on the multifunctional design of pure lattice structures in terms of mechanical properties and energy absorption capacities. However, lattice structures are usually covered by thin exterior densified shells, which can effectively prevent early-stage excessive deformation and thus strengthen the load-carrying capacities [
30,
31]. Cetin et al. [
32‐
34] investigated the energy absorption capacity of lattice-filled thin-walled tubes under impact conditions and determined the corresponding effects of uniform- and graded-lattice infills. Liu et al. [
35] investigated the mechanical behavior of lattice-filled thin-walled tubes with single and multiple cells, in which a pre-manufactured lattice infill was inserted into the thin-shell tubes to form an assembly. It is believed that the mechanical performance of this simple assembly is inferior because of the lack of mechanical joining between the two separate parts. The additively manufactured integrated shell-infill structure can effectively solve the above-mentioned problems and significantly enhance mechanical properties and energy absorption [
36].
This study investigated additively manufactured integrated shell structures with BCC-type porous infill in terms of their mechanical properties and energy absorption capabilities from both experimental and numerical perspectives. The remainder of this paper is organized as follows. The details of the experimental specimen, testing scheme, and corresponding finite element model construction under quasi-static loading conditions are provided in Section
2. The experimental results for different strut diameters are presented and discussed in Section
3. Section
4 presents the finite element modeling strategy selection by comparing simulation results with experimental ones, based on which the shell thickness influnce is studied. Finally, some conclusions are drawn in Section
5.