A New Method of Characterising the Misorientation in Low Angle Boundaries in Hexagonal Crystals

In this work, methods used to define the misorientation between twograins in a hexagonal crystal are presented. Transformation matricesare generally used to define the misorientation and are found to beconvenient and accurate in most cases. However, in the analysis oflow angle boundaries, it is very difficult to obtain data todetermine the transformation matrix accurately. A new method isdescribed which was developed to overcome this problem and thetechnique is demonstrated using the analysis of a boundary inTi₃Al.     

Oscillatory shearing of a class of elastic-plastic materials

Summary For a special class of elastic-plastic materials, it is shown that infinitesimal oscillatory shearing motions can be sustained without the application of body forces. Hardening, softening and perfectly plastic responses are considered.

---

Zusammenfassung Für eine spezielle Klasse von elastisch-plastischen Materialien wird gezeigt, daß infinitesimale oszillatorische Scherbewegungen ohne die Anwendung von Körperkräften aufrecht erhalten werden können. Härtung, Enthärtung und ideale plastische Reaktionen werden betrachtet.

     

Pressure dependency,strength-differential effect,and plastic volume expansion in metals

Within the framework of a purely mechanical rate-type theory of finitely deforming elastic-plastic materials, a special set of constitutive equations is introduced. These equations include a dependence both on mean normal stress and on plastic strain, and involve non-normality of plastic strain-rate. They accommodate both the strength-differential effect and plastic volume expansion. Values of the material coefficients in the constitutive equations are approximately determined with the help of published experimental data for AISI 4330 steel. The plastic strain-rate is shown to have a large non-normal component, resulting in a small plastic volume expansion. The theory is in reasonable agreement with experiment for plastic strains up to about 2% in magnitude. Further experiments are suggested so that the constitutive coefficients can be completely and accurately determined.     

A constitutive restriction related to convexity of yield surfaces in plasticity

Summary An implication of the work assumption of Naghdi and Trapp is established for finitely deforming elastic-plastic materials. For a special class of materials, for which the plastic strain rate is normal to the yield surface in stress space, the result ensures convexity of the latter yield surface.

---

Zusammenfassung Unter der Voraussetzung der Arbeits-Hypothese von Naghdi und Trapp wird für endlich deformierbares elastisch-plastisches Material eine Konsequenz gezogen.Danach wird eine spezielle Klasse von Materialien betrachtet, für die die plastische Dehnungsrate senkrecht auf eine Fläche gerichtet ist. Diese Fläche umschließt den elastischen Bereich der sechsdimensionalen räumlichen Spannungen. Das Ergebnis zeigt, daß diese Konsequenz eine Konvexität dieser Fläche garantiert.

     

A Study of High and Low Angle Boundaries in Ti3Al

High and low angle boundaries have been examined in Ti₃Al using atransmission electron microscope. The misorientations between thegrains were measured accurately and dislocation arrays were imagedwithin these boundaries. An analysis of the low angle boundarydemonstrates that its structure consists of an array of dislocationswith Burgers vectors equal to crystal translation vectors. This arrayaccommodates the angular deviation from the perfect crystallinestructure. The high angle boundary imaged in this specimen alsodisplayed dislocation contrast and the misorientation between thegrains was measured. However, reference structures accommodating thecorresponding deviation could not be unambiguously identified in theobserved dislocation array. The problems of relating the dislocationstructure in hexagonal materials to misorientation relationships arediscussed.     

Spectrophotometric field monitor for the determination of nitrate in river water : Statistical analysis of the results from a nine-month field trial

The results from a 9-month field trial with a spectrophotometric nitrate monitor on the River Frome in Dorset are presented. River water was analysed every 30 min throughout the 273 days of the trial and at least one valid result was obtained on 92% of the days. A complete 30-min interval sampling record was obtained on 34% of the days. The reliability of the monitor and the reasons for failure are discussed. The advantages of this approach to nitrate monitoring over a manual sampling programme are also considered.