Ecologically Driven Ultrastructural and Hydrodynamic Designs in Stomatopod Cuticles

Ecological pressures and varied feeding behaviors in a multitude of organisms have necessitated the drive for adaptation. One such change is seen in the feeding appendages of stomatopods, a group of highly predatory marine crustaceans. Stomatopods include “spearers,” who ambush and snare soft bodied prey, and “smashers,” who bludgeon hard‐shelled prey with a heavily mineralized club. The regional substructural complexity of the stomatopod dactyl club from the smashing predator Odontodactylus scyllarus represents a model system in the study of impact tolerant biominerals. The club consists of a highly mineralized impact region, a characteristic Bouligand architecture (common to arthropods), and a unique section of the club, the striated region, composed of highly aligned sheets of mineralized fibers. Detailed ultrastructural investigations of the striated region within O. scyllarus and a related species of spearing stomatopod, Lysiosquillina maculate show consistent organization of mineral and organic, but distinct differences in macro‐scale architecture. Evidence is provided for the function and substructural exaptation of the striated region, which facilitated redeployment of a raptorial feeding appendage as a biological hammer. Moreover, given the need to accelerate underwater and “grab” or “smash” their prey, the spearer and smasher appendages are specifically designed with a significantly reduced drag force.     

Material properties of brachiopod shell ultrastructure by nanoindentation

Mineral-producing organisms exert exquisite control on all aspects of biomineral production. Among shell-bearing organisms, a wide range of mineral fabrics are developed reflecting diverse modes of life that require different material properties. Our knowledge of how biomineral structures relate to material properties is still limited because it requires the determination of these properties on a detailed scale. Nanoindentation, mostly applied in engineering and materials science, is used here to assess, at the microstructural level, material properties of two calcite brachiopods living in the same environment but with different modes of life and shell ultrastructure. Values of hardness (H) and the Young modulus of elasticity (E) are determined by nanoindentation. In brachiopod shells, calcite semi-nacre provides a harder and stiffer structure (H approximately 3-6 GPa; E=60-110/120 GPa) than calcite fibres (H=0-3 GPa; E=20-60/80 GPa). Thus, brachiopods with calcite semi-nacre can cement to a substrate and remain immobile during their adult life cycle. This correlation between mode of life and material properties, as a consequence of ultrastructure, begins to explain why organisms produce a wide range of structures using the same chemical components, such as calcium carbonate.     

A simplified method for charpy impact testing near liquid helium temperature

A simplified method of examining the impact properties of materials below 5 K is proposed.     

An Experimental Method for Dynamic Delamination Analysis of Composite Materials by Impact Bending

An improved experimental method for characterizing dynamic delamination growth in composite structures has been developed and verified using high speed photography and explicit finite element simulation. The method is based on a three-point bending device. End notch flexure carbon fiber composite beam specimens were subjected to both quasi-static and impact rates of Mode II loading. The experimental results showed no significant strain rate dependency of the delamination fracture toughness. This important result complements the scarce and conflicting data available in the literature, and serves as a reference for calibration of numerical modeling strategies.     

Q500钢焊接接头断裂韧性K_C与冲击功KV_2的相关性统计规律

采用深缺口宽板拉伸试验测定了4种板厚规格(20 mm、32 mm、40 mm和60 mm)Q500钢焊接接头在不同温度下的断裂韧性KC,对32组断裂韧性值及对应试验温度下的冲击功KV2值的相关性进行了统计分析,结果表明,断裂韧性KC与KV2/t近似呈线性关系,其拟合方程为KC=80.6+7.23·KV2/t。     

Highly Impact-Resistant Silk Fiber Thermoplastic Composites

Silk fibers combine good stiffness and strength with a very high strain to failure and are as such highly promising to realize composites with high impact resistance. It is shown that to realize this potential it is quite beneficial to employ matrix materials of high strain to failure, particularly thermoplastic matrices. High impact resistance is thus achieved, well above the values for the pure matrices. Below the glass-transition temperature of the thermoplastic matrix, the impact energy absorption decreases. The adhesion between fiber and matrix also plays a significant role; lower adhesion typically increases the low-velocity penetration impact resistance, due to the spread of damage. Finally, the fiber architecture is pivotal; when a woven fabric is used which is unbalanced in strength, the impact resistance reduces in correspondence with the weakest material direction. A quasi-isotropic layup has a lower capacity for deformation than a balanced woven configuration which likely explains the observed lower penetration impact resistance.     

HAP／Y－TZP复相生物陶瓷研究

羟基磷灰石，是一种具有优秀生物活性的生物材料，但作为承受负荷的骨组织替代物时，缺乏良好的力学性能．本文采用湿化学法制备ＨＡＰ及ＨＡＰ／Ｙ－ＴＺＰ复相粉体，通过热压工艺，以期改善ＨＡＰ的力学性能，分别进行上皮组织、成纤维细胞与膜片联合培养试验．结果表明：含４０ｗｔ％Ｙ－ＴＺＰ的ＨＡＰ复相陶瓷，其抗弯强度和断裂韧性均比同种工艺得到的ＨＡＰ提高７４％和９０％；上皮组织与膜片贴覆性好，不延缓细胞的生长，成纤维细胞与膜片接种良好．     

Nature‐Inspired Lightweight Cellular Co‐Continuous Composites with Architected Periodic Gyroidal Structures

Shell‐core cellular composites are a unique class of cellular materials, where the base constituent is made of a composite material such that the best distinctive physical and/or mechanical properties of each phase of the composite are employed. In this work, the authors demonstrate the additive manufacturing of a nature inspired cellular three‐dimensional (3D), periodic, co‐continuous, and complex composite materials made of a hard‐shell and soft‐core system. The architecture of these composites is based on the Schoen's single Gyroidal triply periodic minimal surface. Results of mechanical testing show the possibility of having a wide range of mechanical properties by tuning the composition, volume fraction of core, shell thickness, and internal architecture of the cellular composites. Moreover, a change in deformation and failure mechanism is observed when employing a shell‐core composite system, as compared to the pure stiff polymeric standalone cellular material. This shell‐core configuration and Gyroidal topology allowed for accessing toughness values that are not realized by the constituent materials independently, showing the suitability of this cellular composite for mechanical energy absorption applications.

     

A novel biomimetic approach to the design of high-performance ceramic–metal composites

The prospect of extending natural biological design to develop new synthetic ceramic–metal composite materials is examined. Using ice-templating of ceramic suspensions and subsequent metal infiltration, we demonstrate that the concept of ordered hierarchical design can be applied to create fine-scale laminated ceramic–metal (bulk) composites that are inexpensive, lightweight and display exceptional damage-tolerance properties. Specifically, Al₂O₃/Al–Si laminates with ceramic contents up to approximately 40 vol% and with lamellae thicknesses down to 10 µm were processed and characterized. These structures achieve an excellent fracture toughness of 40 MPa√m at a tensile strength of approximately 300 MPa. Salient toughening mechanisms are described together with further toughening strategies.     

结构型吸波材料的动载断裂韧性

用改进的Hopkinson测试系统和适合于动载断裂的夹具，测量了结构型吸波复合材料的断裂韧性，给出了系统参数(包括载荷-时间特性、应力强度因子响应特性和起裂时间特性)的确定方法．在纯树脂、普通玻璃钢和结构型吸波复合材料的性能测试中发现，纯树脂、普通玻璃钢和结构型吸波复合材料等结构型吸波材料的起裂点的选择具有较大的特殊性，其起裂时间和动态断裂韧性明显高于普通玻璃钢复合材料．这种比较高的裂纹扩展阻力或止裂作用来源于吸波粒子的引入．     

热处理对Cr17Ni2钢组织和冲击韧性的影响

本文研究了热处理理论对 Cr17Ni2钢组织和冲击韧性的影响,结果表明,将淬火温度提高至1050℃以上,可大大提高冲击韧性。晶界和相界上(Cr、Fe)_(23)C_6碳化物的溶解是冲击韧性增加的主要原因;此外,板条间残留奥氏体薄膜对冲击韧性提高也有贡献。冲击断口的结构可反映断裂特征的组织情况。考虑到室温力学性能,作者建议了合适的热处理工艺,生产中虚用效果良好。     

A new approach for evaluating crack growth resistance curve of mode II delamination by doubly end-notched tension tests

Quantitative determination of interlaminar fracture toughness that governs onset and growth of delamination is essential for engineering of composite materials and structures. This study proposes a new approach to evaluate both the initial fracture toughness and the crack growth resistance property of pure mode II delamination by tensile tests of specimens having two initial cracks, which were conceived from double-lap joints. The proposed test method achieves stable growth of mode II delamination using a fundamental testing system. This study presents the specimen configuration, the theory to evaluate the energy release rate, and experiment results. The mode II initial fracture toughness measured by the present approach agreed well with the results of conventional end-notched flexure tests. Furthermore, the crack growth resistance curves were evaluated by unloading-reloading tests of the proposed doubly end-notched tension specimens.     

含环氧-SiC复合微/纳米纤维的层合板制备及其力学性能

应用同轴静电纺丝技术制备环氧包覆纳米SiC 复合微/ 纳米纤维, 将该复合微/ 纳米纤维收集成无纺布薄膜引入层合板层间界面并固化成型, 研究其对层合板力学性能的影响。采用扫描电子显微镜(SEM) 和透射电子显微镜( TEM) 分析了微/ 纳米纤维的形貌和结构, 并测试了微/ 纳米纤维薄膜的拉伸性能。应用三点弯曲、短梁剪切和简支式冲击实验测定了层合板的弯曲性能、层间剪切强度和冲击韧性。结果表明, 一定厚度及一定SiC 含量的微/ 纳米纤维无纺布薄膜对层合板的力学性能无显著影响。      

冲击能量对ESSO试验结果的影响

对90mm厚EH47船用钢板进行了不同冲击能量下的梯度温度型ESSO试验以分析冲击能量对试验结果的影响.结果表明,采用下限冲击能量测得的-10℃止裂韧性值与双重拉伸试验所测值基本一致,但根据WES:2815-2014规范确定的上限冲击能量测得的止裂韧性值明显低于前两者测得的结果,建议后续在ESSO试验中针对90mm厚钢板选用冲击能量下限值进行试验.     

A status report on delamination resistance testing of polymer-matrix composites

The development of fracture mechanics test methods for the determination of delamination resistance or fracture toughness of fiber-reinforced, polymer-matrix composites is an active area of research. The emphasis in this review is on standardisation of test methods. Recent developments leading towards new standardized test procedures will be presented, complementing and updating earlier reviews.     

复合材料层板+θ/-θ层间断裂韧性研究

本文讨论了纤维增强复合材料层板沿+θ/-θ层间断裂韧性的研究方法;提出在满足一定力学条件时,可沿用机械载荷实验方法测得G_C中“纯机械部分”G_m;结合数值方法计算得出“纯温度部分”G_T,从而得到G_C.给出一个针对DCB试验的充分条件,据此设计铺层并对T300/648和T300/QY8911进行试验和分析(θ=0～30°)、讨论了大变形的影响并提出一个新的修正系数.结合θ对G_C的影响及断口微观形貌作了进一步讨论.     

Al2O3基多角柱状陶瓷复合材料的延缓型断裂

研究了以SiC为界面层的Al2O3基多角柱状陶瓷复合材料的断裂韧性以及断裂功,发现该材料的断裂能显著提高。通过观察裂纹扩展路径以及断裂形貌,分析了多角柱状复合材料的断裂行为,在弯曲强度和韧性测试中,这一材料在适当的载荷容量下,展示出延缓型的断裂行为和非脆性的失效方式。     

GH4169合金的低温冲击试验

对GH4169高温合金边缘和中心部位进行了低温冲击试验,比较晶粒大小对合金冲击功的影响,进一步进行室温冲击试验,比较室温冲击和低温冲击冲击功的大小。同时还对径锻试样和热连轧试样低温冲击所需要的冲击功进行对比,并用SEM观察了冲击断口的表面。结果表明:晶粒越细小,所用的冲击功越大;低温冲击和室温冲击所用的冲击功几乎一样;热连轧试样低温韧性要远远好于径锻试样,冲击端口为韧窝断口。