Impact Performance Research of Re-Entrant Octagonal Negative Poisson’s Ratio Honeycomb with Gradient Design

Based on the traditional re-entrant honeycomb,a novel re-entrant octagon honeycomb(ROH)is proposed.The deformation mode of the honeycomb under quasi-static compression is analyzed by numerical simulation,and the results are in good agreement with the experimental ones.The deformation modes,mechanical properties,and energy absorption characteristics of ROH along the impact and perpendicular directions gradient design are investigated under different velocities.The results indicated that the deformation mode of ROH is affected by gradient design along the direction of impact and impact speed.In addition,gradient design along the direction of impact can increase the initial peak stress of ROH and accelerate its densification phase.Gradient design perpendicular to the impact direction can enhance the energy absorption performance of ROH,especially for ROH,with wall thickness increasing from the inside outwards.Compared to ROH with uniform wall thickness at the same relative density,ROH with a gradient design can increase the plateau stress by over half.With the elevation of impact velocity,the plateau stress and specific energy absorption exhibit an upward trend,aligning with the dynamic performance pattern observed in conventional honeycombs.The results can be used as a reference for the design and application of honeycomb and provide a new idea for developing more efficient and reliable energy-absorbing materials.

In-Plane Impact Dynamics Analysis of Re-Entrant Honeycomb with Variable Cross-Section

Due to the unique deformation characteristics of auxetic materials(Poisson’s ratioμ<0),they have better shock resistance and energy absorption properties than traditional materials.Inspired by the concept of variable crosssection design,a new auxetic re-entrant honeycomb structure is designed in this study.The detailed design method of re-entrant honeycomb with variable cross-section(VCRH)is provided,and five VCRH structures with the same relative density and different cross-section change rates are proposed.The in-plane impact resistance and energy absorption abilities of VCRH under constant velocity are investigated by ABAQUS/EXPLICIT.The results show that the introduction of variable cross-section design can effectively improve the impact resistance and energy absorption abilities of auxetic re-entrant honeycombs.The VCRH structure has better Young’s modulus,plateau stress,and specific energy absorption(SEA)than traditional re-entrant honeycomb(RH).The influence of microstructure parameters(such as cross-section change rateα)on the dynamic impact performance of VCRH is also studied.Results show that,with the increase in impact velocity andα,the plateau stress and SEA of VCRH increase.A positive correlation is also found between the energy absorption efficiency,impact load uniformity andαunder both medium and high impact speeds.These results can provide a reference for designing improved auxetic re-entrant honeycomb structures.

Crashworthiness Optimization Design of Thin-Walled Tube Filled with Re-entrant Triangles Honeycombs

A novel re-entrant triangles-filled tube(RTT)is proposed through decoupling structural stiffness and energy absorption.Inner re-entrant triangles are employed to satisfy energy absorption,and outer thin wall is used to acquire high stiffness.This paper starts from establishment of theoretical models between geometric parameters of re-entrant triangles and relative density,equivalent elastic modulus and energy absorption characteristics,which are validated by experiments.On this basis,the optimal geometric parameters of unit cell are sought to maximize unit volume energy absorption and minimize relative density by adopting NSGA-II method.Subsequently,the cross-section of tube with optimal stiffness is obtained with targets for maximizing axial stiffness and lateral stiffness by employing static topology optimization method.To verify the proposed optimization method,RTT is analyzed and compared with positive Poisson’s ratio foam-filled tube(PFT),non-filled traditionally optimized tube(NTT)and pre-optimized square tube(PST).The results show that the novel RTT can improve stiffness and energy absorption performance simultaneously.Compared with the positive Poisson’s ratio material,re-entrant triangles honeycomb shows superior advantages in energy absorption.In comparison with the PFT,energy absorption of the RTT increases by 17.23%,and the peak crush force reduces by 5.04%.Therefore,the proposed decoupling design method demonstrates superiority in satisfying various performance requirements simultaneously.

Perturbation Solutions for Thermal Process of Honeycomb Regenerator

A parameter perturbation for the unsteady-state heat-transfer characteristics of honeycomb regenerator is presented. It is limited to the cases where the storage matrix has a small wall thickness so that no temperature variation in the matrix perpendicular to the flow direction is considered. Starting from a two-phase transient thermal model for the gas and storage matrix, an approximate solution for regenerator heat transfer process is derived using the multiple-scale method for the limiting case where the longitudinal heat conduction of solid matrix is far less than the convective heat transfer between the gas and the solid. The regenerator temperature profiles are expressed as Taylor series of the coefficient of solid heat conduction item in the model. The analytical validity is shown by comparing the perturbation solution with the experiment and the numerical solution. The results show that it is possible for the perturbation to improve the effectiveness and economics of thermal research on regenerators.

Energy Absorption Characteristics of a Novel Asymmetric and Rotatable Re-entrant Honeycomb Structure

Based on the symmetric re-entrant honeycomb(S-RH)structure with negative Poisson’s ratios,a novel asymmetric and rotatable re-entrant honeycomb(AR-RH)structure was proposed.Both the S-RH structure and AR-RH structure were produced by the 3D printing technology.Through experimental test and finite element simulation,the deformation mechanism and energy absorption characteristics of the AR-RH structure and the S-RH structure with negative Poisson’s ratios at different impact velocities were compared.The experimental test and finite element simulation results show that the novel AR-RH structure with negative Poisson’s ratios has stronger energy absorption capacity than the S-RH structure,and it has been verified that the rotatability of AR-RH can indeed absorb energy.Furthermore,the degree of asymmetry of the AR-RH structure was discussed.

成形法制备半蜂窝波形条的有限元模拟

航空工业上采用的以成形法成形半蜂窝波形条的方式,成形的波形条结构均匀、精度高、工艺简单。根据某厂生产波形条的工艺,利用非线性有限元法开发了成形法的有限元模型,运用该模型对现场的实际成形过程进行仿真计算,得到与现场实测相吻合的结果。比较板坯在单、双主动辊加载的条件下,成形结果的优劣性。在此基础上,对影响成形结果的主要因素进行分析。

耐热合金蜂窝等效热导率的实验研究

耐热合金蜂窝夹芯结构是高超音速飞行器热防护系统外面板的理想候选方案。针对Hastelloy X耐热合金蜂窝夹芯结构开展了稳态传热实验,通过控制加热板温度,获得了一组热平衡时蜂窝夹芯结构的热、冷面温度,结合Stefan-Bolt-zmann定律和大空间自然对流实验关联式,采用热阻分析方法得到了Hastelloy X耐热合金蜂窝随温度变化的宏观等效热导率,并采用Swan-Pittman半经验模型预测了该蜂窝的等效热导率,与实验结果对比一致性较好。

薄壁蓄热器最大相对温度和最佳切换时间

用基于单参数摄动的半解析数值计算法研究薄壁蓄热器结构参数对传热性能的影响。研究表明:存在最大相对温度和最佳切换时间;最大相对温度与气流通道长度成正比;通道内周长的变化,会导致最大相对温度的改变;最佳切换时间与间壁厚度成正比;壁厚1.0 mm时最佳切换周期解析值2.5 s和高温空气气化中间试验的4 s及低氧弥散燃烧工业试验的10 s基本吻合。证实了用渐近解析法进行蜂窝陶瓷蓄热器结构设计和操控优化的可行性。

面内冲击荷载下半凹角蜂窝的抗冲击特性

半凹角蜂窝结构因其零泊松比特征,具有独特的变形方式。将其与传统正泊松比(正六边形)蜂窝以及负泊松比(凹角)蜂窝在面内冲击荷载作用下的抗冲击性能进行对比分析,揭示出零泊松比效应对动力学性能的影响。在给定胞元几何参数(长细比)的情况下,分析了3种蜂窝构型在不同冲击速度下的变形特征,得出半凹角蜂窝的零泊松比特性使结构的局部变形带以"Ⅰ"型为主。根据一维冲击波理论,推导出半凹角蜂窝的平均抗压强度理论公式,与有限元结果进行对比,验证了该方法的有效性。数值结果表明,半凹角蜂窝的抗冲击性能介于正六边形蜂窝和凹角蜂窝之间。通过在半凹角蜂窝内部增加直杆,设计出一种新型零泊松比蜂窝,进一步提高了蜂窝结构的抗冲击性能,可为其他结构优化设计提供一定的理论参考。

Mn-Ce/(CC-A)@12TiO_2整体式蜂窝催化剂的制备及脱硝性能研究

以氨水预处理后的堇青石蜂窝陶瓷为基体,采用半原位溶胶-凝胶工艺制备涂覆TiO_2涂层的Mn-Ce/(CC-A)@12TiO2整装脱硝催化剂,在80～260℃,NOx转化率达90%以上。N2吸脱附、XRD、TG-DSC等分析测试表明,TiO_2主要以结构完整的锐钛矿晶型存在,促进了活泼氧物质的生成,提高了催化活性。SEM图像表明,催化剂表面TiO_2涂层上具有裂纹和粗糙表面,有利于三维结构以及更多孔结构的形成,为反应物与活性位之间相互作用产生更多的活性中间体,从而促进反应速率提供了适宜的场所。EDS研究显示,催化剂Mn-Ce/(CC-A)@12TiO2中TiO_2表面形成的弱结晶Mn-Ce混合氧化物可能有利于Mn与Ce的微观协同效应,提高中间体的形成。

Dynamic crushing behavior and energy absorption of hybrid auxetic metamaterial inspired by Islamic motif art

Auxetic honeycomb structures are promising metamaterials with outstanding mechanical properties,and can be potentially used in energy absorption applications.In this study,a novel modified re-entrant hybrid auxetic metamaterial inspired by Islamic motif art is designed by integrating four-pointed double re-entrant motifs with symmetric semi-hexagonal unit cells to achieve a high energy absorption capacity(EAC).Theoretical analyses and numerical simulations are performed to examine the dynamic crushing behavior of the four-pointed double re-entrant combined structure(FDRCS).The developed finite element models(FEMs)are validated by the experiments under quasi-static compression.The deformation mode and stress-strain curves are further studied under low,medium,and high crushing velocities.The theoretically predicted plateau stress of the FDRCS under different crushing velocities is consistent with the numerical simulation results.The crushing stress and the EAC of the FDRCS are influenced by the geometric parameters and crushing velocities.The FDRCS exhibits a negative Poisson's ratio(NPR),owing to the four-point re-entrant structure(RES).Moreover,the specific energy absorption(SEA)of these structures is higher than that of nonauxetic hexagonal and auxetic re-entrant structures,owing to the generation of more plastic hinges that dissipate more energy during dynamic crushing.

半内凹蜂窝结构的等效理论和拉伸性能研究

半内凹蜂窝结构具有零泊松比等特性,是六边形蜂窝结构和内凹蜂窝结构组成的混合形式。因此,半内凹蜂窝单元的变形特性可以通过六边形蜂窝单元(正角度)和内凹蜂窝单元(负角度)的变形耦合获得。基于六边形蜂窝单元和内凹蜂窝单元的弯曲、拉伸、铰接和剪切变形等不同机制,考虑单元壁厚的影响,建立了半内凹蜂窝单元的变形机制,并推导出半内凹蜂窝结构的面内变形力学性能等效理论,实现对其面内不同方向弹性模量和泊松比的预测。利用有限元方法分析了几何参数(倾斜臂长l、垂直臂长h、角度α、角度β、结构厚度d和单元壁厚t)对半内凹蜂窝结构的面内拉伸性能(弹性模量和泊松比)的影响。对比有限元模拟结果与等效理论预测结果,验证了等效理论模型的有效性和准确性。对比不同等效理论预测结果,表明完善考虑不同变形机制以及壁厚影响,对于准确预测面内拉伸性能的重要性。

装配式钢结构住宅体系的优化研究

为了加快建筑产业现代化的步伐,解决当前钢结构住宅存在的问题,通过实地考察和研究针对装配式钢结构住宅体系提出几种新的做法。该体系柱采用矩形管内灌混凝土;梁采用开孔扁梁,钢筋桁架组合楼板下承于钢梁下翼缘,既能保证钢梁的稳定性又提高了钢梁的防火性能;梁柱采用半刚性节点缓解了节点处焊接导致的应力集中,提高了安装效率。该体系能有效解决钢结构住宅的防火、防腐以及保温隔音等问题。