材料力學(xué)課件：第1章 材料力學(xué)基本概念

1、材 料 力 學(xué)第1章 材料力學(xué)基本概念1.1 材料力學(xué)的基本任務(wù)1.2 變形固體的基本假設(shè)1.3 桿件的內(nèi)力與截面法1.4 應(yīng)力與應(yīng)變的概念1.5 材料力學(xué)簡史1.1 材料力學(xué)的基本任務(wù)構(gòu)件分類載荷的分類桿件變形的基本形式材料力學(xué)的基本任務(wù)* 材料的機械（力學(xué)）性質(zhì)返回構(gòu)件分類塊* 軸線返回載荷的分類* 按作用方式分集中力分布力* 按作用性質(zhì)分靜載（荷）動載（荷）返回桿件變形的基本形式軸向拉壓剪切扭轉(zhuǎn)彎曲桿軸梁返回 在滿足強度、剛度、穩(wěn)定性的要求下，以最經(jīng)濟的代價，為構(gòu)件確定合理的形狀和尺寸，選擇適宜的材料，而提供必要的理論基礎(chǔ)和計算方法。返回材料力學(xué)的基本任務(wù)* 強度 抵抗斷裂或過量塑性變形

2、的能力返回圖2 樁斷裂的典型裂紋圖1 砌體結(jié)構(gòu)房屋破壞的實例橋梁下部結(jié)構(gòu)的嚴重損傷是引起橋梁倒塌返回返回* 剛度抵抗彈性變形的能力返回立式彎曲中心lsw32 固特機械76S大半徑自由成型彎曲橋面彎曲成w形返回南京一處樓房開裂 房屋變形鑒定顯示“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. 壓電納米機電諧振器Nanoelectromechanical resonatorThey can be applied in the detection of amyloid(淀粉體) 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)十角準晶的示意圖模型，顯示十面和雙面的取向，2折面沿10倍方向周期性，沿2倍方向非周期；(B)摩擦研究中懸臂梁的原理圖和掃描幾何學(xué)。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和納米管力學(xué)性能的方法綜述。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 漏電流）（ stress

11、ed gate 應(yīng)力閥門）MOSFET-Embedded Microcantileversfor Measuring Deflectionin Biomolecular Sensorsmetal-oxide semiconductor field-effect transistor (MOSFET)金屬氧化物半導(dǎo)體場效應(yīng)晶體管用于生物分子傳感器偏轉(zhuǎn)測量的MOSFET嵌入式微懸臂梁* 穩(wěn)定性 保持其原有平衡狀態(tài)的能力返回* 工程實例* 雙人自行車* 杭州灣跨海大橋（36公里100年）* 海洋石油鉆井平臺斷為兩截的米格-29!返回* 材料的機械（力學(xué)）性質(zhì)彈性、塑性、沖擊韌性.材料力學(xué)的研究手段*

12、 理論分析* 實驗材料力學(xué)采用的力學(xué)模型* 變形固體返回1.2 變形固體的基本假設(shè)* 連續(xù)性物質(zhì)毫無空隙地充滿了物體所在的空間* 均勻性物體內(nèi)，各處的力學(xué)性能完全相同* 各向同性各個方向的力學(xué)性質(zhì)完全相同* 小變形條件變形很小，在受力分析時可忽略返回1.3 桿件的內(nèi)力與截面法* 內(nèi)力 附加內(nèi)力* 截面法六字真言截開、代替、平衡返回1.4 應(yīng)力與應(yīng)變的概念* 應(yīng)力 一點處的內(nèi)力集度返回M* 單位：p* 線應(yīng)變* 角應(yīng)變梁彎曲時的位移、變形及應(yīng)變五CDE位移線位移角位移變形線變形角變形應(yīng)變線（正）應(yīng)變角（切）應(yīng)變CDE1.5 材料力學(xué)簡史傳統(tǒng)具有柱、梁、檁ln 、椽chun的木制房屋結(jié)構(gòu)古代建筑結(jié)構(gòu)一返回古代建筑結(jié)構(gòu)建于唐末（857年）的山西五臺山佛光寺東大殿1.5 材料力學(xué)簡史古代建筑結(jié)構(gòu)建于遼代（1056年）的山西應(yīng)縣佛宮寺釋迦塔塔高9層共67.31米，用木材7400噸900多年來歷經(jīng)數(shù)次地震不倒，現(xiàn)存唯一木塔1.5 材料力學(xué)簡史古代建筑結(jié)構(gòu)2200年以前建造的都江堰安瀾索橋 1.5 材料力學(xué)簡史古代建筑結(jié)構(gòu)建于隋代（605年）的河北趙州橋橋長64.4米，跨徑37.02米，用石2800噸1.5 材料力學(xué)簡史材料力學(xué) 獨立出