Analysis of Optimal Roll Tensioning for Circular Saw Stability

When a circular saw is used to cut wood, a substantial and increasingly important fraction of the raw material is wasted because of the excessive width of the sawcut. The process of "roll tensioning" is studied here, whereby sawblade thickness, and hence material loss, can be significantly reduced while still maintaining sawblade stability. A theoretical model is developed that accurately describes the localized plastic deformation that takes place during roll tensioning, the associated residual stresses, and the resulting changes in sawblade natural frequencies. Experimental measurements of the residual stresses and natural frequencies confirm the theoretical predictions. The mathematical model allows reliable prediction of optimal tensioning conditions for any given saw operating state and development of automated control of the tensioning process. An example is presented in which the thickness of an optimally tensioned circular sawblade is 33% smaller than the thickness of an untensioned sawblade of equivalent transverse stability

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

Residual Stress Determination of Cast Aluminium Benchmark Components Using Strain Relief Techniques

Background: Residual stress development in precipitation strengthened aluminium foundry alloys has seen little attention, despite the prevalence of their use over a wide array of applications. Objective: This study aims at the evaluation of the residual stress in a cast aluminium benchmark that develops during precipitation heat treatment and determines the preferable stress relaxing techniques for such applications.Methods: The stress states in the as-cast, T4 and T6 tempers of the same AlSi7Cu0.5Mg (A356 with 0.5 wt% Cu) sample were determined through a novel application of the contour method, standard hole drilling, deep hole drilling and incremental deep hole drilling. Results: The results of all measurement techniques lie within approximately 40 MPa for all regions available for comparison, with the greatest differences occurring between the contour method and deep hole drilling for the T6 component. It is shown that the peak tensile residual stresses are almost identical between the heat-treated components (75 MPa), but the distribution and magnitude of compressive residual stress are found to be significantly different. Conclusions: Among the measurement techniques evaluated, the contour method and incremental hole drilling are found to be more suitable for T6 temper, while all techniques perform equally well for T4 temper due to its relatively low strength. It is hypothesised that the difference between the as-cast and heat-treated samples is due to solution heat treatment and quenching, while the difference in T4 and T6 tempers is attributed to the response to ageing