A note on Moiré gratings by a stacked card method

An unusual method is described in which a stack of alternating plain and painted cards forms gratings for Moiré applications. It is quite simple and versatile so that almost anyone may adopt it with ease and a minimum of expertise.     

A note on evaluating the fracture energy of thin ceramic layers by cleavage

A new method is suggested aimed at evaluating _IC , the mode I fracture energy of thin brittle layers. The fracture energy is obtained by cleaving a ceramic layer sandwiched between two metallic layers, joined by brazing. The driving force for the cleavage is the mismatch between the thermal expansion coefficients of the ceramic and the metallic layers. The fracture energy is calculated from the strain energy released in the cleaved sandwiched structure. Based on this method, the fracture energy of the ceramic layer can be evaluated if the cleavage temperature is known, either by visual inspection or instrumentation. The method is effective for thin ceramic layers, for the determination of the fracture energy of cleavage planes of single crystal brittle solids (provided the cleavage plane is within the plane of the specimen), and for the interfacial fracture energy of ceramic/ceramic or ceramic/metal joints. In order to verify and calibrate the test method, polycrystalline alumina thin plates were joined by brazing with Ti-6Al-4V alloy using Wesgo Cusil ABA alloy. The appropriate selection of materials and geometry, and some difficulties arising from this method are discussed.     

A note on cylindrical wave diffraction by a perfectly conducting strip in a homogeneous bi-isotropic medium

The diffraction of an electromagnetic wave by a perfectly conducting finite strip in a homogeneous bi-isotropic medium is studied in an improved form. The problem is solved by using the Wiener–Hopf technique and Fourier transform. The scattered field in the far zone is determined by the method of steepest descent.     

A note on fatigue damage assessment by x-ray diffraction techniques for a 304L stainless steel specimen

The progress of fatigue damage in type 304L solution treated stainless steel was studied by surface residual stress measurements and measurements of the formation of martensite, as determined from x-ray diffraction techniques. The specimen was subjected to tension-tension (R=0.1) cycling in air at a maximum stress _max=422 MPa, which was approximately 160% off the yield stress. The initial longitudinal residual stress distribution was determined for 13 locations along the gage length and found to vary around –80±17 MPa (compression). After several fatigue cycles, the residual stress changes to approximately +115±17 MPa (tension). At about 7% of the life (N/N _f =0.07), the variation of the residual stress along the gage length reaches a minimum. With additional cycling, the residual stress first drops, reaching a minimum at approximately 10% of the life (100±8 MPa), then increases to a maximum at between 20 and 40% of the life (125±18MPa), followed by a marked relaxation to a minimum of 90±18 MPa at approximately 65% of the life. The surface martensite content of the sample continuously increases from its initial value of around 0.6%, first slowly up to 10% of the total fatigue life, and more rapidly thereafter to final failure. On the basis of additional measurements of the residual stress and martensite content as a function of depth below the surface, surface layer hardening of austenite and martensite is suggested as the principal reason for the residual stress development.     

A note on an assertion by E. Gutiérrez-Peña and A.F.M. Smith (Test, 1997, p.87)

In estimating the discrete parameter of a Binomial distribution, to choose a truncated Poisson model as the prior distribution of this parameter is shown to be unsuitable. This research has been partially supported by Proyect DGES-PB97-1403-C03