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1.
为探究水牛角的结构性能关系,基于上海同步辐射光源搭建了高分辨原位CT系统,对水牛角角鞘进行初始表征和准静态压缩下的实时表征,并通过Top-Hat方法提取了角鞘内孔洞三维形貌。结果显示,水牛角角鞘孔隙率在1%左右,椭圆柱状孔洞沿牛角生长方向排列成线,首尾相连却并未连通,均匀分布在波浪状片层之间。孔洞特征椭球的轴长分布满足对数正态分布,长轴和短轴的长度均值分别为7μm和3μm。原位CT结果表明,角鞘在屈服之后,初始孔洞首先扩张而形成微裂纹,随后微裂纹沿着片层界面由外向内发生桥接,片层发生局部屈曲和层间开裂,形成宏观裂纹,导致角鞘内裂纹密度急剧上升。片层之间不仅存在大量纤维黏接(提高了层间拉伸/剪切强度),而且孔洞互不连通,这些因素抑制了层间裂纹的快速传播,使得各处裂纹只能独立缓慢发展而无法贯通样品。波浪状片层使裂纹传播路径更加曲折,层间屈曲增加了片层摩擦耗能。这些机制使得牛角表现出加工硬化,也是牛角在纵向方向呈现优良韧性的主要原因。  相似文献   
2.
运用ANSYS/LS_DYNA软件分析了聚能射流对充液结构的毁伤,初步获得了药型罩壁厚和材料等参数对聚能战斗部水下作用的影响特性。药型罩壁厚在0.04Dk~0.06Dk(Dk为装药直径)之间形成的射流对充液防护结构具有较优的侵彻性能;当δ<0.04Dk时,杆流成型结构较差,在水中的动能抗衰减性能较低;δ>0.06Dk时,射流的初始动能低,靶后效果差。药型罩可采用纯铁、紫铜和钽3种材料,其中纯铁射流的侵彻能力最高,钽射流在水中的动能抗衰减性能最好,紫铜射流具有较好的综合性能。  相似文献   
3.
武强  张庆明  龚自正  任思远  刘海 《爆炸与冲击》2021,41(2):021406-1-021406-9
以二级轻气炮作为加载手段,针对以PTFE/Al活性材料为防护屏的Whipple防护结构,开展不同弹丸尺寸、不同碰撞速度的超高速撞击实验。利用激光阴影照相设备,获得并分析了碎片云特性;通过回收的防护结构靶板,研究了活性材料防护结构超高速撞击条件下的后板损伤特性;通过与经典Christiansen撞击极限方程对比,获得活性材料Whipple结构防护性能,并拟合得到新型防护结构的撞击极限曲线。结果表明,相较于同面密度铝合金材料,活性材料超高速撞击条件下的冲击起爆反应使得碎片云中具有侵彻能力的碎片大幅减少,从而显著提升航天器的防护能力,撞击速度为2.31 km/s时最大可提升45%。  相似文献   
4.
In this study, ultrasound-assisted extraction of polyphenols from C. cicadae was optimized by response surface methodology (RSM). The optimized conditions were determined as extraction time of 39 min, liquid-to-solid ratio of 1:29 g/mL, extraction temperature of 69 °C and ethanol concentration of 55% with a yield of 21.9 mg gallic acid equivalent/g dry weight. Four resins were used for polyphenol purification. D101 resin had the highest ratio of adsorption and was further applied in polyphenol purification test. A total of 19 different phenolic compounds were identified by LC-MS, including 12 phenolic acids and 7 organic acids. In addition, C. cicadae polyphenols displayed higher antioxidant activity in vitro and anti-aging activity of C. elegans in vivo. Lastly, C. cicadae polyphenols showed the potential to protect DNA from oxidative damage. Overall, our results suggest that polyphenols from C. cicadae may be considered as novel sources of anti-oxidation, anti-aging and recommended as reagents to protect DNA from oxidative damage in food and pharmaceutical industries.  相似文献   
5.
通过三点弯动态冲击实验和数值模拟方法,研究了分支交错层状仿生复合材料的动态断裂韧性。首先设计并制备了分支交错层状仿贝壳复合材料试样,即将一种脆性刚性材料和一种橡胶类材料分别作为复合材料的硬质层和软胶层;随后采用改进的分离式Hopkinson压杆装置进行了三点弯冲击实验;接着讨论了初始冲击速度、硬质材料长宽比、软质材料层厚度对复合材料试样动态断裂行为的影响;最后采用ABAQUS有限元数值模拟,研究了不同宽度和不同冲击方向对复合材料试样动态断裂韧性和裂纹扩展的影响。结果表明:随着冲击速度和硬质材料长宽比增加、软胶层厚度减小,裂纹越倾向于沿直线扩展,反之,裂纹越倾向于绕过硬质材料沿着软胶层呈折线扩展;试样的峰值动载荷和起裂时间也随之增大。有限元模拟结果表明:随着结构总宽度的增大,试样断裂韧性增加,裂纹倾向于绕过硬质材料沿着软胶层扩展;采用实验设计的冲击方向时,试样的断裂韧性高于其他方向。  相似文献   
6.
Aimed at the internal short circuit problem due to large deformation of the prismatic lithium-ion battery cell under impact loadings, a simplified battery model was first established. Then the motion equations of velocity and displacement based on the membrane factor method were proposed. With the effects of the face-sheet thickness and the densification region on the normalized final deflection, impact response characteristics of prismatic battery cells were investigated in detail. The results show that, the improved motion equations involving the membrane factor can reflect the dynamic response mechanisms of the prismatic battery cell under impact loadings, and the large deflection under high-speed impact can be predicted. With the increase of the face-sheet thickness, the deflection of the battery cell’s lower part decreases obviously. However, the densification region expands with the face-sheet thickness. The deflection and the densification region of the cell’s lower part both increase with the inner core density of the battery. This proposed impact model provides a theoretical guidance for the multi-functional integrated dynamic design of prismatic battery cells. © 2022 Editorial Office of Applied Mathematics and Mechanics. All rights reserved.  相似文献   
7.
The influence of ultrasound treatment (US) on cellular damage of olive leaf tissue was studied. Mechanical damage and thermal effect of US were characterized. The level of tissue damage was defined by the diffusivity disintegration index ZD based on the diffusivity of solutes extracted from olive leaves differently treated. The Arrhenius form using the temperature dependences of the thermal treatment time within the temperature interval 20–90 °C was observed for the thermal process. The corresponding activation energy ΔUT was estimated as 57 kJ/mol. The temperature dependences of electrical conductivity were measured for extracts of intact and maximally treated olive leaves. Then the diffusivity disintegration index ZD and total phenolic compounds recovery for three studied US powers were calculated (100, 200, and 400 W). The results evidenced that the mechanically stimulated damage in olive leaf tissue can occur even at a low US power of 100 W if treatment time is long enough (t = 3.5 h). The US treatment noticeably accelerated the diffusion process mechanically in addition to its thermal effect. Trials in aqueous solution revealed the dependence of polyphenols extraction on damage level with respect to the US power applied.  相似文献   
8.
High-reflective multilayer laser coatings are widely used in advanced optical systems from high power laser facilities to high precision metrology systems. However, the real interface quality and defects will significantly affect absorption/scattering losses and laser induced damage thresholds of multilayer coatings. With the recent advances in the control of coating design and deposition processes, these coating properties can be significantly improved when properly engineered the interface and defects. This paper reviews the recent progress in the physics of laser damage, optical losses and environmental stability involved in multilayer reflective coatings for high power nanosecond near-infrared lasers. We first provide an overview of the layer growth mechanisms, ways to control the microstructures and reduce layer roughness, as well as the nature of defects which are critical to the optical loss and laser induced damage. Then an overview of interface engineering based on the design of coating structure and the regulation of deposition materials reveals their ability to improve the laser induced damage threshold, reduce the backscattering, and realize the desirable properties of environmental stability and exceptional multifunctionality. Moreover, we describe the recent progress in the laser damage and scattering mechanism of nodule defects and give the approaches to suppress the defect-induced damage and scattering of the multilayer laser coatings. Finally, the present challenges and limitations of high-performance multilayer laser coatings are highlighted, along with the comments on likely trends in future.  相似文献   
9.
Zhongyu Shi 《中国物理 B》2022,31(5):54701-054701
The phenomenon of droplet impact on an immiscible liquid is encountered in a variety of scenarios in nature and industrial production. Despite exhaustive research, it is not fully clear how the immiscibility of the liquid on which a droplet impacts affects the crown evolution. The present work experimentally investigates the evolution kinematics of a crown formed by the normal impact of a camellia oil droplet on an immiscible water layer. Based on discussion of dynamic impact behaviors for three critical Weber numbers (We), the radius of the crown and its average spreading velocity are compared with those of previous theoretical models to discuss their applicability to the immiscible liquid. The evolution kinematics (morphology and velocity) are analyzed by considering the effects of the We and layer thickness. Furthermore, the ability of crown expansion in radial and vertical directions is characterized by a velocity ratio. The results show that our experimental crown radius still follows a square-root function of evolution time, which agrees with the theoretical predictions. The dimensionless average spreading velocity decreases with We and follows a multivariate power law, while the dimensionless average rising velocity remains constant. The velocity ratio is shown to linearly increase with We, demonstrating that the rising movement in crown evolution gradually enhances with We. These results are helpful for further investigation on the droplet impact on an immiscible liquid layer.  相似文献   
10.
朱本占  张静  唐苗  黄春华  邵杰 《化学进展》2022,34(1):227-236
卤代醌是一类卤代芳烃类环境污染物的致癌中间体,也是在饮用水中新发现的氯化消毒副产物。我们最近发现卤代醌和 H2O2 或有机氢过氧化物体系可以不依赖过渡金属离子,而产生高活性的羟基/烷氧自由基和醌氧/醌碳自由基。目前尚不清楚这些卤代醌类致癌物和氢过氧化物共存能否诱导 DNA 产生氧化损伤和修饰,以及其潜在的分子机制是什么。我们的研究发现 DNA 在四氯-1,4-苯醌/H2O2体系中可被氧化产生 8-氧脱氧鸟苷、DNA 链断裂和三种甲基氧化产物,这些反应不依赖过渡金属离子,且由于卤代醌与 DNA 的嵌入作用而导致其氧化作用增强。其他卤代醌也观察到了类似的现象,而且通常比经典的 Fenton 体系更有效。我们进一步将研究从纯化的 DNA 扩展到了活细胞的基因组 DNA。同时还发现卤代醌和有机氢过氧化物(如叔丁基过氧化氢或在正常生理条件下产生的 13S-过氧羟基-9Z,11E-十八碳二烯酸(13-HPODE))共存时,可通过独特的醌氧自由基介导机制诱导 DNA 氧化生成致突变性更强的咪唑啉酮类产物 dIz。这些发现为解释普遍存在的卤代醌类致癌中间体和消毒副产物的潜在基因毒性、致突变性和致癌性提供了新思路。  相似文献   
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