Mechanics of materials CHAPTERI3 IDYNAMI CLOADS
1 Mechanics of Materials
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CHAPTER 13 DYNAMIC LOADS □§13-1 BASIC CONCEPTS □§13-2 DYNAMIC RESPONSE ABOUT THE PROBLEM OF ACCELERATIVE MOTIONS 习§13-3 DYNAMIC RESPONSE ABOUT THE PROBLEM OF IMPACT LOADS
CHAPTER 13 DYNAMIC LOADS §13–1 BASIC CONCEPTS §13–2 DYNAMIC RESPONSE ABOUT THE PROBLEM OF ACCELERATIVE MOTIONS §13–3 DYNAMIC RESPONSE ABOUT THE PROBLEM OF IMPACT LOADS
第十三章动荷载 §13-1基本概念 §13-2加速运动问题的动响应 §13-3冲击荷载问题的动响应
第十三章 动荷载 §13–1 基本概念 §13–2 加速运动问题的动响应 §13–3 冲击荷载问题的动响应
DYNAMIC LOAD §13-1 BASIC CONCEPTS 1、 Dynamic loa The loads don t change with time(or change very stably and slowly )and acceleration of each member is zero or may be neglected, this kind of the loads are called static loads. The loads change sharply w ith time and the velocity of the member changes obviously the member produces the inertia force ) this kind of load is loads are called dynamic loads 2、 Dynamic responses: Various responses (such as stress, strain, displacement and so on )ofthe member under the action of dynamic loads are called dynamic responses. Experiment prove that Hooke law applied validly under static loads may be applied to the case of dynamic loads with Estat ic=edvnamic as long as the stress does not exceed the proportional limit
1、Dynamic loads： §13-1 BASIC CONCEPTS 2、Dynamic responses： The loads don’t change with time(or change very stably and slowly) and acceleration of each member is zero or may be neglected ，this kind of the loads are called static loads. The loads change sharply with time and the velocity of the member changes obviously（the member produces the inertia force），this kind of load is loads are called dynamic loads. Various responses (such as stress、strain、displacement and so on)of the member under the action of dynamic loads are called dynamic responses. Experiment prove that Hooke’law applied validly under static loads may be applied to the case of dynamic loads with Estatic=Edynamic as long as the stress does not exceed the proportional limit
§13-1基本概念 一、动载荷: 载荷不随时间变化(或变化极其平稳缓慢)且使构件各部件 加速度保持为零(或可忽略不计),此类载荷为静载荷。 载荷随时间急剧变化且使构件的速度有显著变化(系统产生 惯性力),此类载荷为动载荷, 二、动响应: 构件在动载荷作用下产生的各种响应(如应力、应变、位 移等),称为动响应。 实验表明:在静载荷下服从虎克定律的材料,只要应力不 超过比例极限,在动载荷下虎克定律仍成立且E静一E动
一、动载荷： 载荷不随时间变化（或变化极其平稳缓慢）且使构件各部件 加速度保持为零（或可忽略不计），此类载荷为静载荷。 载荷随时间急剧变化且使构件的速度有显著变化（系统产生 惯性力），此类载荷为动载荷。 §13-1 基本概念 二、动响应： 构件在动载荷作用下产生的各种响应（如应力、应变、位 移等），称为动响应。 实验表明：在静载荷下服从虎克定律的材料，只要应力不 超过比例极限 ,在动载荷下虎克定律仍成立且E静=E动
DYNAMIC LOAD 3 Dynamic load coefficient Dynamic response D ynamic load coeficient K R=K, Static response 4> Classification of the dynamic stress 1).Simple dynamic stress: The acceleration can be determined. We may apply the method of kineto static" to solve this kind of problems 2). Impact load: The velocity changes sharply in a very short time. In this case the acceleration can not be determined. We must apply the energy method to solve this kind of problems 3).Alternating stress: Stress changes periodically with time. It belongs to the fatigue problem 4). Vibration problems: There are many methods to solve this kind of problems
3、Dynamic load coefficient： d =Kd j Static response Dynamic response Kd = 4、Classification of the dynamic stress： 1).Simple dynamic stress： The acceleration can be determined. We may apply the“method of kineto static” to solve this kind of problems. 3).Alternating stress：Stress changes periodically with time. It belongs to the fatigue problem. 4).Vibration problems：There are many methods to solve this kind of problems. Dynamic load coefficient 2).Impact load：The velocity changes sharply in a very short time. In this case the acceleration can not be determined. We must apply the “energy method” to solve this kind of problems；
三、动荷系数: 动荷系数x动响应 静响应 O=K,O 四、动应力分类: 1.简单动应力:加速度可以确定,采用“动静法”求解 2.冲击载荷:速度在极短暂的时间内有急剧改变,此时,加 速度不能确定,要采用“能量法”求解; 3.交变应力:应力随时间作周期性变化,属疲劳问题。 4.振动问题:求解方法很多
三、动荷系数： d =Kd j 静响应 动响应 动荷系数Kd = 四、动应力分类： 1.简单动应力： 加速度可以确定，采用“动静法”求解 。2.冲击载荷： 速度在极短暂的时间内有急剧改变，此时，加 速度不能确定，要采用“能量法”求解； 3.交变应力： 应力随时间作周期性变化，属疲劳问题。 4.振动问题： 求解方法很多
DYNAMIC LOAD 8 13-2 DYNAMIC RESPONSE OF THE PROBLEM OF ACCELERATIVE MOTIONS Principle of the method: D Alembert's principle Method of kineto statics D Alembert's principle think there is inertial force on the body in un- equilibrium. The direction of the inertial force is opposite to the acceleration of the body and the magnitude of the inertial force is the product of the mass and the acceleration of the body. After the inertial force is applied on the body the dynamic problem may be dealt with the static problem in form, which is called the method of kineto statics
§13-2 DYNAMIC RESPONSE OF THE PROBLEM OF ACCELERATIVE MOTIONS Principle of the method：D’Alembert’s principle ( Method of kineto statics ） D’Alembert’s principle think there is inertial force on the body in unequilibrium. The direction of the inertial force is opposite to the acceleration of the body and the magnitude of the inertial force is the product of the mass and the acceleration of the body. After the inertial force is applied on the body the dynamic problem may be dealt with the static problem in form, which is called the method of kineto statics
§13-2加速运动问题的动响应 方法原理: DAlembert' s principle (动静法) 达朗伯原理认为:处于不平衡状态的物体,存在惯性 力,惯性力的方向与加速度方向相反,惯性力的数值等于 加速度与质量的乘积。只要在物体上加上惯性力,就可以 把动力学问题在形式上作为静力学问题来处理,这就是动 静法
§13-2 加速运动问题的动响应 方法原理：D’Alembert’s principle ( 动静法 ） 达朗伯原理认为：处于不平衡状态的物体，存在惯性 力，惯性力的方向与加速度方向相反，惯性力的数值等于 加速度与质量的乘积。只要在物体上加上惯性力，就可以 把动力学问题在形式上作为静力学问题来处理，这就是动 静法