Thus far we have discussed mechanical loading and the stresses and strains caused by that We noted, however, that the environment can have an effect on the behavior of materials and structures. Let's first consider:

Summarizing what we've looked at in elasticity, we have: 15 equations in 15 unknowns 3 equilibrium -6 strains -6 strain-displacement -3 displacements

There are many structural configurations where we do not have to deal with the full 3-D case. First let's consider the models Let's then see under what conditions we can apply them A. Plane Stress

As we've previously noted, we may often want to describe a structure in various axis systems. This involves... Transformations (Axis, Deflection, Stress, Strain, Elasticity Tensors) e.g., loading axes material principal axis Figure 7.1 Unidirectional Composite with Fibers at an Angle

We do not characterize materials by their E mnpq The Emnpa are useful in doing transformations, manipulations, etc. We characterize materials by their \ENGINEERING CONSTANTS\ (or, Elastic Constants)

Sources of Stresses and Strains Depends on type of structure Aircraft

Let's first review a bit... from Unified, saw that there are basic considerations in elasticity: 1. Equilibrium 2. Strain-Displacement 3. Stress- Strain Relations (Constitutive Relations)

Recall the definition of stress: o stress =\intensity of internal force at a point\ Figure 3.1 Representation of cross-section of a general body

Need to study structural mechanics to design properly to prevent failure There is no doubt that any of the disciplines of Aeronautics and Astronautics can contribute to an accident -engine failure -etc. But, the vast majority of non-human induced accidents is due to structural

人类有史以来就向往着能够自由飞行。古老的神话故事诉说着人类早年的飞行梦,而梦想的飞行方式都 是原地腾空而起,像现代直升机那样既能自由飞翔又,能悬停于空中,并且随意实现定点着陆。例如哪 阿拉伯人的飞毯,希腊神的战车,都是垂直起落飞行器