Experimental data objectives, sampling procedures

When the experimentalist set an ambitious objective to evaluate micromechanical properties quantitatively, he will predictably encounter a few fundamental problems. At first, the continuum description which is usually used in contact mechanics might be not applicable for contact areas as small as 1 -10 nm [116,117]. Secondly, since most of the polymers demonstrate a combination of elastic and viscous behaviour, an appropriate model is required to derive the contact area and the stress field upon indentation a viscoelastic and adhesive sample [116,120]. In this case, the duration of the contact and the scanning rate are not unimportant parameters. Moreover, bending of the cantilever results in a complicated motion of the tip including compression, shear and friction effects [131,132]. Third, plastic or inelastic deformation has to be taken into account in data interpretation. Concerning experimental conditions, the most important is to perform a set of calibrations procedures which includes the (x,y,z) calibration of the piezoelectric transducers, the determination of the spring constants of the cantilever, and the evaluation of the tip shape. The experimentalist has to eliminate surface contamination s and be certain about the chemical composition of the tip and the sample. 

Before adopting statistical tests to assess the reliability of data, outliers should be first analyzed carefully to identify any anomaly in instrament fidelity, calibration, procedure, environmental conditions, recording, etc. The first objective is to reject an outlier based on physical evidence that the data point was unrepresentative of the sample population. If this exercise fails to identify probable cause (or if details on the experimental methods are unavailable), Chauvenet s criterion may be applied to assess the reliability of the data point (Holman 2001). Simply put, the criterion reconunends rejecting a data point if the probability of obtaining the deviation is less than the reciprocal of two times the number of data points—l/(2n). For an outlier smaller than the mean, the data point may be rejected when ... 

The remaining part of this chapter will review the three most common direct methods for measuring fiber-matrix adhesion, focusing on the sample preparation and fabrication, the experimental protocols and the underlying theoretical analyses upon which evaluation of these methods are based. In addition, finite-element nonlinear analyses and photoelastic analyses will be used to identify differences in the state of stress that is induced in each specimen model of the three different techniques. In order to provide an objective comparison between the three different techniques to measure the interfacial shear strength for the prospective user, data and a carbon fiber-epoxy resin system will be used as a baseline system throughout this chapter, However, these methods and procedures can be applied for adhesion measurements to any fiber-matrix combination. 

---