Abstract
Foam-filled two-dimensional lattice structures were designed, and their compression performance was studied relative to corresponding structures without the foam. The experimental results showed that the compressive load of foam-filled lattice structures improved greatly compared with foam-unfilled specimens. The specific energy absorption (SEA) of foam-unfilled specimens exceeded that of the corresponding foam-filled lattice structure. The maximum energy absorption efficiency of the foam-unfilled lattice structure exceeded 1.5, while that of the foam-filled lattice structure was less than 1. The theoretically predicted compression performance was close to the experimental results. The wood-based lattice structure exhibited excellent specific strength and stiffness compared with other structures.
Download PDF
Full Article
Compression Properties of Two-dimensional Wood-based Dowel Lattice Structure Filled with Polyurethane Foam
Gaoyuan Ye, Qingyuan Xu, Yanpeng Cheng, Zixuan Fan, Qi Li, Jiankun Qin, Shuguang Li, and Yingcheng Hu *
Foam-filled two-dimensional lattice structures were designed, and their compression performance was studied relative to corresponding structures without the foam. The experimental results showed that the compressive load of foam-filled lattice structures improved greatly compared with foam-unfilled specimens. The specific energy absorption (SEA) of foam-unfilled specimens exceeded that of the corresponding foam-filled lattice structure. The maximum energy absorption efficiency of the foam-unfilled lattice structure exceeded 1.5, while that of the foam-filled lattice structure was less than 1. The theoretically predicted compression performance was close to the experimental results. The wood-based lattice structure exhibited excellent specific strength and stiffness compared with other structures.
Keywords: Lattice structure; Compression property; Specific strength; Specific stiffness
Contact information: Key Laboratory of Bio-based Material Science and Technology of the Ministry of Education of China, College of Material Science and Engineering, Northeast Forestry University, Harbin 150040, China; *Corresponding author: yingchenghu@nefu.edu.cn
INTRODUCTION
A lattice structure is composed of nodes and bar elements connected between nodes. It features high specific strength, high specific stiffness, good energy absorption performance, and other excellent properties. Such structures have been applied in aerospace, the automotive industry, for high-speed railways, and in other fields (Fan et al. 2009; Fan et al. 2010; Yang et al. 2013). Lattice structures have many configurations, such as tetrahedral (Kooistra et al. 2004), pyramidal (Zok et al. 2004; Biagi and Bart-Smith 2007; Queheillalt and Wadley 2009), and the Kagome (Zhang et al. 2018; Lee et al. 2019). Wang et al. (2010) fabricated a mold and used the hot-pressing technology to integrate carbon fibers into a pyramidal lattice structure for compression experiments. The failure mode of the lattice structure was mainly yield and fracture of the core. Zhang et al. (2012) fabricated a carbon fiber tetrahedral lattice structure with thermally expanding silicone rubber; this lattice structure has a higher specific strength than several metal lattice structures. Queheillalt and Wadley (2005) used a stainless-steel hollow tube as core to prepare a hollow lattice through welding. The hollow lattice had performance features beyond those of the solid lattice, such as an improved anti-buckling ability. Sun and Gao (2013) improved the carbon fiber pyramid lattice structure, and this improved structure achieved better comprehensive performance. Fan et al. (2014) prepared a pyramidal lattice structure with glass fiber and conducted a compression experiment, demonstrating that the multi-level lattice structure had a higher ductility and energy absorption efficiency with regard to energy absorption.
Lattice structures generally consist of metal or carbon fibers, and research on wood-based lattice structures is relatively rare. In this experiment, wood was used to investigate the compression performance of lattice structures with cores of different length. The structure of the lattice filled with polyurethane foam was investigated via compression tests. The specific strength, specific stiffness, and other characteristics of the lattice structures were analyzed.
EXPERIMENTAL
Preparation of Two-Dimensional Lattice Structure
Oriented strand board (OSB) was used as the panel for the lattice structure. It was purchased from Dongfang Port International Wood, Ltd. (Beijing) and made from pine- wood shavings. Birch dowel (Harbin Tengzhan Wood Industry, Ltd., Harbin, China) was used as the core. The OSB was drilled, and the core was inserted and glued with epoxy resin. The preparation process is shown in Fig. 1. After the two-dimensional lattice structure was prepared, materials A and B (consisting of polyurethane foam) were mixed, stirred for 15 s, and poured into the core layer of the lattice structure to obtain the corresponding foam-filled lattice structure. A foam density of 20kg/m3 was used. The E-44 type epoxy resin was purchased from Nantong Xingxing Synthetic Materials, Ltd., Harbin, China. Foam was purchased from Shandong Yisheng Polyurethane Foam, Ltd., Harbin, China.
Fig. 1. Preparation process of the lattice structure
Experiment
Three sizes of lattice structures and their corresponding foam-filled specimens were compressed. The sizes of the specimens are shown in Table 1. The A, B, and C lattice structures filled with foam were named A1, B1, and C1 lattice structures, respectively. The length and width of the A, B, and C specimen panels were 150 × 50 mm, 220 × 50 mm, and 300 × 50 mm, respectively. A schematic diagram of the lattice structure is shown in Fig. 2. L is the length of the core, d is the diameter of the core, ω is the included angle between the core and the panel, and t is the spacing between the core.
Table 1. Size and Relative Density of the Lattice Structure
Fig. 2. Schematic diagram of the lattice structure
Fig. 3. Compression diagram of lattice structure of (a) unfilled and (b) filled foam
Four test pieces were used for each group of A, B, C, A1, B1, and C1 lattice structures. The quasi-static compression response of samples was studied. Figure 3 shows the compression test diagram, indicating that the compression force was applied from the top of the structure. The compression experiment was conducted on a universal mechanical testing machine (Shenzhen Sans Material Testing Co., Ltd, Microcomputer controlled electronic universal testing machine C61.104, Shenzhen, China) according to ASTM C365/C365M-11a (Cote et al. 2007) standard with a compression speed of 2 mm/min.
RESULTS AND DISCUSSION
Compression Experimental Results
The load-displacement curves of the three lattice structures A, B, and C and the corresponding foam-filled lattice structures A1, B1, and C1 are shown in Fig. 4. Part (a) shows two load-displacement curves: the load-displacement curve of the A lattice represents one type, and those of B and C represent a different type. The load-displacement curve of the A lattice has three stages: an elastic stage, a platform stage where the load gradually decreased, and a densification stage. When the load was first applied, the force increased rapidly with displacement. After the force reached the maximum strength, the core was destroyed, and the force decreased with displacement, finally entering the densification stage. The load-displacement curves of B and C lattice have two stages: an elastic stage and a stage when the load suddenly decreases with displacement. When entering the elastic stage, the force increased rapidly with displacement. After the force reached the peak force, the core broke and the load decreased suddenly. The reason for these two load-displacement curves is as follows: the core diameter to length ratio of the A lattice is large. When the load reached a maximum, the core was damaged but did not break suddenly. The core diameter to length ratio of B and C lattice was small, and when the maximum load had been reached, the core broke, resulting in the failure of the bearing capacity. Figure 4 shows that the peak load followed the order A > B > C. The reason is that the greater the diameter to length ratio of the core, the greater the peak load will be, and the diameter to length follows A > B > C; therefore, the peak load follows A > B > C.
Fig. 4. Load-displacement curves of lattice structure of (a) unfilled and (b) filled foam (the core lengths of A, B, and C structures are 42mm, 102mm, and 162mm, respectively, while the structures of A1, B1, and C1 are obtained by filling the foam with A, B, and C structures, respectively)
The failure diagrams of lattice structures of A, B, and C are shown in Fig. 5. The core of lattice A suffered shear failure in the middle and upper part; the core of lattice B suffered bending failure in the middle part; the core of lattice C suffered buckling failure in the middle part, which resulted in core fracture. The failure modes of the lattice structure were consistent with the corresponding load-displacement curves.