Mechanical methods to determine layer compliances within multilayered composites
- PDF / 205,881 Bytes
- 9 Pages / 612 x 792 pts (letter) Page_size
- 57 Downloads / 210 Views
A comparison of bending and compressive/tensile loading cases of multilayered composites is given. Bending perpendicular to the layer interfaces is suggested as a sensitive and experimentally convenient method for determining the elastic modulus of compliant isotropic layers within a multilayered composite. Different approaches to analyze the strain and compliance behavior of the composite and individual layers are derived. Ranking of the relevant equations with respect to strain sensitivity is made, which favors the bending test perpendicular to the layer interfaces. The derived relationships permit a prediction of the bending behavior and the flexural rigidity of the composite. Furthermore, the properties of a layer within the structure can be determined. Limitations that exist for the bending perpendicular to the layer interfaces in the case of low stiffness of the layers can be overcome using either a compressive or a tensile loading mode. Application of the formulas to buckling and interfacial delamination is considered. Materials, such as plasma-sprayed thermal barrier coatings, that are supposed to behave elastically different in tension and compression are given special consideration. Although determination of elastic moduli is the main interest, in the case of known elastic moduli, the formulas can be used to determine the thickness of individual layers within a composite structure.
I. INTRODUCTION
The modulus of elasticity (E) and for brittle materials, the modulus of rupture (MOR), can be determined using bending or compressive/tensile loading.1,2 The methods are typically applied to isotropic materials using wellestablished mechanical relationships.3 However, in the case of layered composites, the determination of E and MOR of the individual layers from the global data obtained in a test with a composite specimen is still limited and short of theoretical formulation.4,5 Often the data are analyzed on the basis of the elastic relationships for isotropic materials.6 In the following, analytical relationships are derived to determine the elastic modulus of individual isotropic layers within a multilayered composite using bending or compressive/tensile loading, rather than applying the frequently favored indentation technique. The main advantage of the tests over indentation techniques is that the elastic modulus of layers within a sandwich or multilayered structure can be determined. For layers of high elastic modulus, the instrumental and specimen preparation difficulties (uncertainty is proportional to the ratio of roughness to indentation depth) related 1374
http://journals.cambridge.org
J. Mater. Res., Vol. 18, No. 6, Jun 2003 Downloaded: 18 Mar 2015
to the low indentation depth needed to determine the properties of layers can be overcome. Also, the elastic moduli of materials such as plasma-sprayed thermal barrier coatings (TBCs)7 or rocks8 that are supposed to behave differently in tension and compression can be calculated. In addition, the methods given below allow an assessment of the onset of p
Data Loading...
