Off-axis angle

Most comparisons of a failure criterion with failure data will be for the glass-epoxy data shown in Figure 2-36 as a function of off-axis angle 0 for both tension and compression loading [2-21]. The tension data are denoted by solid circles, and the compression data by solid squares. The tension data were obtained by use of dog-bone-shaped specimens, whereas the compression data were obtained by use of specimens with uniform rectangular cross sections. The shear strength for this glass-epoxy is 8 ksi (55 MPa) instead of the 6 ksi (41 MPa) in Table 2-3. 

Determine the character of the Tsai-Hill failure criterion for pure shear loading between off-axis angles of 0° and 90° by examining the characteristics of the result from Problem 2.9.6 using the techniques of Appendix B. That is, this is the shear analog of Problem 2.9.7. 

The tendencies seen are quite general. For small off-axis angles, i.e. nearly perpendicular to the macroscopic surface plane, shading is relatively unimportant and the main deviating effect is due to the variation of the local take-off angle over the surface, with the result that the /(//s ratio is larger than for a flat layer... 

The trend must be to reduce the off-axis angle. Fortunately, if we peek at what has happened previously in the Si and GaAs worlds, the standard was to use off-axis substrates initially, but as the material quality improved, the need for off-axis substrates was reduced and on-axis substrates are now used for epitaxy. This is likely going to be the trend in SiC too. The need for better epitaxial procedures and higher-quality substrates than what is available today is important. 

Seeded sublimation growth is a mature and needed tool for the SiC industry today. There are still major challenges. Specifically, boules will need to be grown on off-axis substrates, or the off-axis angle needs to be eliminated, which will only be possible if a combined effort of improving wafer quality, polishing procedures, and epitaxial procedures is pursued. 

The present paper aims to assess damage in UD GRP composites of various off-axis angles under axial loads. Damage analysis presented in this paper is drastically influenced by void content of the material and it assumes that there should be a direct relationship between the failure of composite material and its void content. 

Keywords GRP Composites, Off-axis angles, Loading level, void content, statistical analysis. 

A statistical analysis based on General Linear Model (GLM) was developed to analyse the influence of loading and off-axis angle on damage of composite laminates. The void content in the composite specimens acted as stress raiser resulting in cracks initiation, propagation and failure as tensile loads progressively applied. Analysis of Variance (ANOVA) was performed for void contents to check the statistical differences caused by the experimental errors. 

According to Eq. (1), seven monotonic tests with various off-axis angles of 0 , 15 , 30 , 45°, 60°, 75° and 90° and at five different loading levels of Untested, PTl, PT2, PT3 and FULL were performed. Multiplying it by five replicates and two views of SEM photography, 350 different tests have been performed. 

Tensile test specimens have been fabricated based on ASTM D 3039 for off-axis angles. The materials chosen for fiber and matrix were E-Glass UD-weaves and ML-506 Epoxy resin, respectively. UD-weave fiber lay-up and test specimen geometry are shown in Figure 1 and Figure 2 ... 

The angle between loading direetion and fibers direction (off-axis angle)... 

P is the slope or coefficient associated with the off-axis angle. P2 is the slope or coefficient associated with the load, is a random error. 

A new approach to predict the failure of UD GRP composites has been developed in this paper. The direct relationship between the void propagation and failure of composite material has been successfully aehieved. The effeet of off-axis angle and loading level on void content was then mathematically described. 

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