It is very important to evaluate the cushioning properties of paper honeycomb sandwich structures for optimizing pack design. The energy absorption diagram is one method to characterize the cushioning properties of materials. In this paper, we investigate energy absorption and develop energy absorption diagrams for paper honeycomb sandwich structures. Based on static compression experiments, the compressive stress-strain curve is simplifi ed into three sections: linear elasticity, plateau and densifi cation. By considering the factors associated with the structure of paper honeycombs, the energy absorption model is obtained and characterized by the thickness-to-length ratio of the honeycomb cell wall. Both theory and experiment show that the compression energy absorption capability increases with the increasing thickness-to-length ratio of the honeycomb cell wall, and a good agreement is achieved between the theoretical and experimental energy absorption curves. The proposed method to develop an energy absorption diagram for paper honeycomb sandwich structures can be used to characterize the cushioning properties and optimize the structures of paper honeycomb sandwiches. Copyright

In this paper, micro-structured polymer parts were efficiently and accurately fabricated by micro-injection molding using a micro-structured mold core machined by wire electrical discharge machining (WEDM). The objective was to realize low-cost mass production and manufacturing of micro-structured polymer products. The regular micro-structured mold core was manufactured by precise WEDM. The micro-structured polymer workpieces were rapidly fabricated by micro-injection molding and the effects of the micro-injection molding process parameters on replication rate and surface roughness of micro-structured polymers were systematically investigated and analyzed. It is shown that the micro-structured polymer can be rapidly and precisely fabricated by the proposed method. The experimental results show the minimum size machining error of the micro-structured mold core and the maximum replication rate of micro-formed polymer were 0.394% and 99.12%, respectively. Meanwhile, the optimal micro-injection molding parameters, namely, jet temperature, melt temperature, injection velocity, holding pressure and holding time were 195 °C, 210 °C, 40 mm/min, 7 Mpa and 5 s, respectively. The surface roughness Ra at the groove bottom and top of the micro-structured polymer workpieces achieved minimum values of 0.805 µm and 0.972 µm, respectively.

The influence of temperature and relative humidity on the moisture content of paper honeycomb sandwich panels was studied, and the ideal three-dimensional diagram between the moisture content of paper honeycomb sandwich panels and the temperature and relative humidity was constructed by the GAB model. The evaluation equation of critical stress and plateau stress were obtained. The results indicate that the moisture content of paper honeycomb sandwich panels rises with the increase of relative humidity and declines with the increase of temperature; as the moisture content increases, the critical stress and plateau stress of paper honeycomb sandwich panels decline linearly; with the increase of the moisture content, the energy absorption of paper honeycomb sandwich panels increased firstly and then decreased; the evaluation equation of critical stress and plateau stress can predict the mechanical properties of paper honeycomb sandwich panels in different temperatures and relative humidities.

Paper honeycomb sandwich panel is an environment-sensitive material. Its cushioning property is closely related to its structural factors, the temperature and humidity, random shocks, and vibration events in the logistics environment. In order to visually characterize the cushioning property of paper honeycomb sandwich panel in different logistics conditions, the energy absorption equation of per unit volume of paper honeycomb sandwich panel was constructed by piecewise function. The three-dimensional (3D) energy absorption diagram of paper honeycomb sandwich panel was constructed by connecting the inflexion of energy absorption curve. It takes into account the temperature, humidity, strain rate, and characteristics of the honeycomb structure. On the one hand, this diagram breaks through the limitation of the static compression curve of paper honeycomb sandwich panel, which depends on the test specimen and is applicable only to the standard condition. On the other hand, it breaks through the limitation of the conventional 2D energy absorption diagram which has less information. Elastic modulus was used to normalize the plateau stress and energy absorption per unit volume. This makes the 3D energy absorption diagram universal for different material sandwich panels. It provides a new theoretical basis for packaging optimized design.

Detecting human behaviours in images of crowded classroom scenes is a challenging task, due to the large variations of humans in scale and pose perspective. In this paper, two modules are proposed to tackle these two variations. First, an attention‐based RoI (region‐of‐interest) extractor is designed to handle scale variation. Feature fusion and attention mechanism are used to improve the RoI feature with more local and global information. Second, a transformation‐based detection head is introduced to handle perspective variation. The spatial transformation is adopted to extract consistent representation under various perspectives. Moreover, since there is a lack of proper datasets for human behaviour detection in classroom scenes, a new dataset is created, namely CLBD. The experiments on the proposed dataset demonstrate that the modules obtain significant improvements of performance over the state‐of‐the‐art detectors.