Why Is It So Challenging to Measure Residual Stresses ?

Background: Residual stresses have a "hidden" character because they exist in a material without the presence of any external loads. They cannot easily be added or subtracted in a quantified manner, as is done when measuring applied stresses, and so are much more challenging to measure. Objective: The objective here is to identify and describe the various features that make residual stress measurement methods challenging and to consider the ways that these challenges can be addressed in practice. Methods: Various of the most common residual stress measurements methods are considered and the challenges associated with them are identified and classified. Results: Five major challenges for residual stress measurements, and the approaches used for their resolution, are identified. Conclusions: Despite the various challenges that need to be overcome, residual stress measurements can be successfully undertaken in practice. The most significant feature for success is a highly skilled and knowledge practitioner.

A build-at-home student laboratory experiment in mechanical vibrations.

The Covid-19 pandemic has caused many university educators to redesign their teaching to online delivery. This can be an effective approach for theoretical and conceptual teaching, but it is challenging to provide practical laboratory experiences. The objective here is to design a hands-on laboratory experience that can safely be undertaken by students remotely and that has substantial educational content. A new experiment was designed featuring a bifilar pendulum that students build themselves from readily available low-cost materials. This simple vibrating system has a surprisingly rich set of interesting physical characteristics that provide several important learning points. Initial trials indicate good student experience with the new experiment, notably an appreciation for the "do-it-yourself" aspect of the apparatus construction. The self-directed features and multiple learning features of the new student experiment make it attractive for use during Covid-19 times and beyond.

Influence of elastic nonlinearity on arterial anastomotic compliance.

This study illustrates how the highly nonlinear elastic behavior of artery wall material can cause unusual structural characteristics that do not occur with a linear-elastic material. An example mathematical model of an end-to-end anastomosis successfully predicts the experimentally observed area of elevated elastic compliance, called the "Para-anastomotic Hypercompliant Zone" (PHZ). The elastic hypercompliance is shown to occur because the anastomosis locally restricts the arterial diameter, thus forcing the adjacent material to remain in a lower strain, and correspondingly a lower stiffness, part of its non-linear stress-strain curve. Elevated elastic compliance can be avoided by locally matching both the arterial diameter and the elastic compliance within the physiological pressure range.