Mechanical Behaviour in the Mushy State during Isothermal Tensile Testing

2006 ◽  
Vol 519-521 ◽  
pp. 1877-1882 ◽  
Author(s):  
Damien Fabrègue ◽  
Alexis Deschamps ◽  
Michel Suéry ◽  
Warren J. Poole
Keyword(s):  
Solid Fraction ◽  
Mechanical Behaviour ◽  
Aluminium Alloys ◽  
Fracture Stress ◽  
Maximum Stress ◽  
Hot Tearing ◽  
Brittle Ductile Transition ◽  
Partial Remelting ◽  
Maximal Stress ◽  
The Difference

In order to improve the understanding of hot tearing during laser welding of aluminium alloys, the rheology of the alloys in the mushy state must be characterized. The present work investigates the mechanical behaviour of the aerospace alloy AA6056 using a specially designed isothermal tensile test in the mushy state. Using a Gleeble thermo-mechanical machine, two different tests have been performed: i) tests during partial remelting and ii) tests after partial solidification at a high cooling rate. These tests have been carried out not only on the 6056 alloy but also on a mix between 6056 and 4047 Al-Si alloy which corresponds to the composition of the nugget of a laser using a filler wire. The increase of the solid fraction results in an increase of the maximum stress and a change on the fracture surface from a smooth dendritic to a more ductile one. Moreover, the alloys exhibit a typical visco plastic behaviour with an increase of the maximal stress with the strain rate. When the test is performed at a particular solid fraction of 0.97, the fracture is more erratic and the ductility is low. The results show the existence of a ductile/brittle/ductile transition with the fraction of solid. The fracture stress is shown to be higher when testing after partial remelting as compared to partial solidification for the same solid fraction. This is due to the difference in microstructure of the mushy zone and more particularly in the connectivity of the solid skeleton. An adapted creep law is used to describe the mechanical behaviour of alloys during the partial remelting test using the fraction of grain boundary wetted by the liquid given by Wray. This law is shown to be irrelevant to the partial solidification tests, as a result of the modified geometry of the liquid phase. From these tests, we have determined a new law relating the solid fraction to the fraction of grain boundaries wetted by the liquid. This law is a useful tool to predict the mechanical behaviour when mechanical loading occurs during solidification.

Grain Refinement and Hot Tearing of Aluminium Alloys - How to Optimise and Minimise

2009 ◽  
Vol 630 ◽  
pp. 213-221 ◽  
Author(s):  
Mark Easton ◽  
David H. StJohn ◽  
Lisa Sweet
Keyword(s):  
Grain Refinement ◽  
Aluminium Alloys ◽  
Hot Tearing ◽  
Key Factors ◽  
Grain Refiner ◽  
Factors Affecting ◽  
Equiaxed Grains

Grain refinement and hot tearing are important key factors affecting the quality of castings. There have been substantial advances in the understanding of both of these phenomena over the last two decades. The paper discusses strategies for obtaining the lowest cost grain refiner addition and provides an explanation for how the refinement of equiaxed grains leads to a reduction in hot tear susceptibility. However, it also provides a warning that adding more grain refiner may not be better for reducing hot tear susceptibility. Alloy factors affecting hot tearing are also discussed. Finally, a list of six key considerations is provided to help casthouse and foundry engineers when trying to optimise grain refinement and reduce hot tearing.

scholarly journals Influence of a Thin Horizontal Weak Layer on the Mechanical Behaviour of Shallow Foundations Resting on Sand

Geosciences ◽  
2021 ◽  
Vol 11 (9) ◽  
pp. 392
Author(s):  
Maurizio Ziccarelli ◽  
Marco Rosone
Keyword(s):  
Bearing Capacity ◽  
Mechanical Behaviour ◽  
Failure Mechanisms ◽  
Shear Bands ◽  
Ultimate Bearing Capacity ◽  
Shallow Foundations ◽  
Foundation Soil ◽  
Weak Layer ◽  
Geotechnical System ◽  
The Difference

The presence of minor details of the ground, including soil or rock masses, occurs more frequently than what is normally believed. Thin weak layers, shear bands, and slickensided surfaces can substantially affect the behaviour of foundations, as well as that of other geostructures. In fact, they can affect the failure mechanisms, the ultimate bearing capacity of footings, and the safety factor of the geotechnical system. In this research, numerically conducted through Finite Element Code Plaxis 2D, the influence of a horizontal thin weak layer on the mechanical behaviour of shallow footings was evaluated. The obtained results prove that the weak layer strongly influences both the failure mechanism and the ultimate bearing capacity if its depth is lower than two to four times the footing width. In fact, under these circumstances, the failure mechanisms are always mixtilinear in shape because the shear strains largely develop on the weak layer. However, the reduction in the ultimate bearing capacity is a function of the difference between the shear strength of the foundation soil and the layer. The presence of a thin weak layer decreases the ultimate bearing capacity up to 90%. In conclusion, this research suggests that particular attention must be paid during detailed ground investigations to find thin weak layers. Based on the obtained results, it is convenient to increase the soil volume investigation to a depth equal to four times the width of the foundation.

Large Stroke Series Compliant Mechanism

2012 ◽  
Vol 490-495 ◽  
pp. 1104-1108 ◽  
Author(s):  
Ming Cai Shan ◽  
Wei Ming Wang ◽  
Shu Yuan Ma ◽  
Shuang Liu
Keyword(s):  
Theoretical Model ◽  
Maximum Stress ◽  
Compliant Mechanism ◽  
Critical Parameters ◽  
Element Analysis ◽  
Flexure Hinges ◽  
Body Model ◽  
System A ◽  
Rigid Body Model ◽  
The Difference

To increase the stroke of precision positioning system, a novel series compliant mechanism is presented which is based on elliptical flexure hinges. Pseudo-rigid-body model and energy method are applied to establish the theoretical model of stiffness and maximum stress, which are critical parameters for the large stroke compliant mechanism. The relationships are analyzed between geometric parameters of the series complaint mechanism, stiffness and maximum stress. According that, the series compliant mechanism is designed with the stroke more than 5mm and stiffness less than 3.2N/mm. The difference is less than 5% between the results of finite element analysis and theoretical model computation, which proves the correctness of the application design.

Microstructural Properties of Common Yew and Norway Spruce Determined with Silviscan

IAWA Journal ◽  
2009 ◽  
Vol 30 (2) ◽  
pp. 165-178 ◽  
Author(s):  
Daniel Keunecke ◽  
Robert Evans ◽  
Peter Niemz
Keyword(s):  
Mechanical Behaviour ◽  
Mechanical Response ◽  
Elastic Anisotropy ◽  
Longitudinal Direction ◽  
Structural Features ◽  
Structure Property ◽  
Tangential Plane ◽  
Cross Sectional ◽  
X Ray ◽  
The Difference

Yew wood holds a special position within the softwoods with regard to its exceptional elasto-mechanical behaviour. Despite a relatively high density, it is highly elastic in the longitudinal direction (the modulus of elasticity is low and the stretch to break high). In the radial-tangential plane, its elastic anisotropy is clearly less pronounced compared to other softwoods such as spruce. Knowledge of the anatomical organisation of yew wood is an indispensable precondition for the correct interpretation of this conspicuous mechanical behaviour. The aim of this study, therefore, was to interpret the difference in elasto-mechanical behaviour of yew and spruce (as a reference) through their relative microstructures as measured by SilviScan, a technology based on X-ray densitometry, X-ray diffractometry and optical microscopy. This system is able to measure a variety of structural features in a wood sample. The results reveal that the elasto-mechanical response of yew is primarily due to large microfibril angles and a more homogeneous cross-sectional tissue composition (regarding tracheid dimensions and density distribution) compared to spruce. With respect to structure-property relationships, it was concluded that yew wood combines properties of normal and compression wood and therefore takes an intermediate position between them.

Analysis of the impact of macrosegregation on hot tearing conditions during DC casting of aluminium alloys

2009 ◽  
Vol 22 (1-4) ◽  
pp. 90-93 ◽  
Author(s):  
K. Ellingsen ◽  
M. M'Hamdi ◽  
D. Mortensen ◽  
H. G. Fjær
Keyword(s):  
Aluminium Alloys ◽  
Hot Tearing ◽  
Dc Casting ◽  
The Impact

Comparative Analysis of Stress of Two Typical Micro-Displacement Control Platform

2014 ◽  
Vol 687-691 ◽  
pp. 382-385
Author(s):  
Xian Chen Tao ◽  
Meng Shao
Keyword(s):  
Comparative Analysis ◽  
Tensile Stress ◽  
Maximum Stress ◽  
Geometric Parameters ◽  
Displacement Control ◽  
The Difference ◽  
The Relationship

This paper selects two typical micro-displacement control platforms,and conducts comparative analysis of strength of their flexible guiding mechanism.Stress expressions of flexible guiding mechanism are respectively derived to obtain the relationship between the maximum stress and geometric parameters and the relationship between tensile stress and bending stress.with moving the same displacement,the difference of stress of the two micro-displacement control platforms is small,and can be ignored.

Biomechanical Analysis of Tendon Suture Techniques

Hand Surgery ◽  
1997 ◽  
Vol 02 (02) ◽  
pp. 93-100
Author(s):  
Kwang Suk Lee ◽  
Kyung Jo Woo ◽  
Jae Young Jeon
Keyword(s):  
Tensile Strength ◽  
Modulus Of Elasticity ◽  
Maximum Stress ◽  
Statistical Significance ◽  
Relative Strength ◽  
Suture Technique ◽  
Biomechanical Analysis ◽  
Suture Techniques ◽  
The Difference ◽  
Group 2

The relative strength of three suture methods of lacerated tendon were measured by mechanical disruption in effort to determine the strength of suture technique. Fifty-four calcaneal tendons of 27 New Zealand white rabbits were transected at mid-portion and repaired with the three suture techniques: group 1: Kessler suture; group 2: Pennington's modified-Kessler suture; and group 3: augmented-Becker suture technique. Each group was composed of 18 calcaneal tendons. Three groups of rabbits, 9 in each, were, respectively, sacrificed immediately after suture, at 2 weeks postoperatively and at 4 weeks postoperatively. The augmented-Becker repair was strongest in tensile strength and maximum stress at immediate operation, 2 weeks postoperatively and 4 weeks postoperatively. The augmented-Becker repair had the highest modulus of elasticity at time of suture, at 2 and at 4 weeks postoperatively. Tensile strength, maximum stress and modulus of elasticity gradually increased from the time of operation to 4 weeks, but the difference was not of statistical significance at 4 weeks.

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