材料力学课件：第1章 材料力学基本概念

1、材 料 力 学第1章 材料力学基本概念1.1 材料力学的基本任务1.2 变形固体的基本假设1.3 杆件的内力与截面法1.4 应力与应变的概念1.5 材料力学简史1.1 材料力学的基本任务构件分类载荷的分类杆件变形的基本形式材料力学的基本任务* 材料的机械（力学）性质返回构件分类块* 轴线返回载荷的分类* 按作用方式分集中力分布力* 按作用性质分静载（荷）动载（荷）返回杆件变形的基本形式轴向拉压剪切扭转弯曲杆轴梁返回 在满足强度、刚度、稳定性的要求下，以最经济的代价，为构件确定合理的形状和尺寸，选择适宜的材料，而提供必要的理论基础和计算方法。返回材料力学的基本任务* 强度 抵抗断裂或过量塑性变形

2、的能力返回图2 桩断裂的典型裂纹图1 砌体结构房屋破坏的实例桥梁下部结构的严重损伤是引起桥梁倒塌返回返回* 刚度抵抗弹性变形的能力返回立式弯曲中心lsw32 固特机械76S大半径自由成型弯曲桥面弯曲成w形返回南京一处楼房开裂 房屋变形鉴定显示“安全”返回Fig. 1. Schematic of the piezoelectric microcantilever motion.Note that the light gray microcantilever is inequilibrium, while the darkgray microcantilever is not samplePiez

3、oelectric layerAtomic Force Microscopy (AFM) AFM tipFig. 1. Schematic representation of a piezoelectric nanoelectromechanical resonator. 压电纳米机电谐振器Nanoelectromechanical resonatorThey can be applied in the detection of amyloid(淀粉体) growth , quantum ground state and spin manipulation piezoelectric lami

4、nated micro system Fig. 1. (a) A schematic view of the micro system,(b)deflected element of micro system beam,and(c)System crosssection when 0 xlp Fig. 1. (A) Schematic model of a decagonal Al-Ni-Co quasicrystal, showing the orientation of decagonal and twofold planes. The 2-fold plane is periodic a

5、long the 10-fold direction and aperiodic along the 2-fold direction. (B) Schematic of the cantilever and the scanning geometry during friction studiesStrong friction anisotropy is found when the twofold surface of an atomically clean aluminum-nickel-cobalt quasicrystal slides against a thiol-passiva

6、ted titanium-nitride tip. Friction along the aperiodic direction is one-eighth as much as that along the periodic direction. This anisotropy, which is about three times as large as the highest value observed in anisotropic crystalline surfaces, disappears after the surface is oxidized in air. These

7、results reveal a strong connection between interface atomic structure and the mechanisms by which energy is dissipated, which likely include electronic or phononic contributions, or both.1.(A)十角准晶的示意图模型，显示十面和双面的取向，2折面沿10倍方向周期性，沿2倍方向非周期；(B)摩擦研究中悬臂梁的原理图和扫描几何学。Fig. 1. Overview of the approach used to p

8、robe mechanical properties of NRs and nanotubes.Schematic of beam bending with an AFM tipSchematic of a pinned beam with a free endstructurally isolated silicon carbide (SiC) nanorods (NRs)研究NRS和纳米管力学性能的方法综述。Fig. 1. (A) Schematic of the interaction between probe and target molecules on an embedded-M

9、OSFET cantilever system. The silicon nitride cantilever is a reference, and the gold-coated one is used as a sensing cantilever. Specific biomolecular interactions between receptor and target bend the cantilever. Magnified view of embedded MOSFET in cross section shows stressed gate region when cant

10、ilever bends, resulting in change of drain current due to conductivity modulation of the channel underneath the gate. (B) Schematic of change in a MOSFET drain current upon probe-target binding. (C) Change in drain current over time due to deflection of a microcantilever. （drain current 漏电流）（ stress

11、ed gate 应力阀门）MOSFET-Embedded Microcantileversfor Measuring Deflectionin Biomolecular Sensorsmetal-oxide semiconductor field-effect transistor (MOSFET)金属氧化物半导体场效应晶体管用于生物分子传感器偏转测量的MOSFET嵌入式微悬臂梁* 稳定性 保持其原有平衡状态的能力返回* 工程实例* 双人自行车* 杭州湾跨海大桥（36公里100年）* 海洋石油钻井平台断为两截的米格-29!返回* 材料的机械（力学）性质弹性、塑性、冲击韧性.材料力学的研究手段*

12、 理论分析* 实验材料力学采用的力学模型* 变形固体返回1.2 变形固体的基本假设* 连续性物质毫无空隙地充满了物体所在的空间* 均匀性物体内，各处的力学性能完全相同* 各向同性各个方向的力学性质完全相同* 小变形条件变形很小，在受力分析时可忽略返回1.3 杆件的内力与截面法* 内力 附加内力* 截面法六字真言截开、代替、平衡返回1.4 应力与应变的概念* 应力 一点处的内力集度返回M* 单位：p* 线应变* 角应变梁弯曲时的位移、变形及应变五CDE位移线位移角位移变形线变形角变形应变线（正）应变角（切）应变CDE1.5 材料力学简史传统具有柱、梁、檩ln 、椽chun的木制房屋结构古代建筑结构一返回古代建筑结构建于唐末（857年）的山西五台山佛光寺东大殿1.5 材料力学简史古代建筑结构建于辽代（1056年）的山西应县佛宫寺释迦塔塔高9层共67.31米，用木材7400吨900多年来历经数次地震不倒，现存唯一木塔1.5 材料力学简史古代建筑结构2200年以前建造的都江堰安澜索桥 1.5 材料力学简史古代建筑结构建于隋代（605年）的河北赵州桥桥长64.4米，跨径37.02米，用石2800吨1.5 材料力学简史材料力学 独立出