UV-Induced non-local stress relaxation in bimaterial systems

2003 ◽  
Author(s):  
H.N.J. Fernando ◽  
L. Wosinski ◽  
B. Jaskorzynska ◽  
M. Dainese ◽  
J. Canning
Keyword(s):  
Stress Relaxation ◽  
Local Stress ◽  
Non Local

Modelling Recovery and Recrystallisation Kinetics after Intercritical Deformation in 0.19 wt% C 1.5 wt% Mn Steel

2004 ◽  
Vol 467-470 ◽  
pp. 329-334 ◽  
Author(s):  
A. Smith ◽  
A. Miroux ◽  
Haiwen Luo ◽  
Jilt Sietsma ◽  
Sybrand van der Zwaag
Keyword(s):  
Stress Relaxation ◽  
Stress Distribution ◽  
Strain Distribution ◽  
Local Stress ◽  
Stress Strain ◽  
Simple Modification ◽  
Single Grain ◽  
Grain Model ◽  
Mn Steel ◽  
Kinetics Of

The softening kinetics of a 0.19 wt% C 1.5 wt% Mn steel deformed at two intercritical temperatures have been characterised using the stress relaxation technique. Recrystallisation of intercritical austenite has been modelled using a single grain model (Chen et al., 2002 [1]), whilst recovery of both intercritical austenite and ferrite has been modelled using a model in the literature [Verdier et al., 1999 [2]). The models are combined to predict the overall softening kinetics with a rule of mixtures formulation. Comparison of the model with experiment shows significant deviations. The reasons are discussed with reference to the mixture rule and to the local stress-strain distribution which exists in the deformed samples. A simple modification to the model is proposed which takes into account the effect of a local stress distribution in deformed austenite.

Notch-Strengthening Phenomenon Under Creep-Fatigue Loading Conditions

1999 ◽  
Vol 122 (1) ◽  
pp. 15-21 ◽  
Author(s):  
N. Merah
Keyword(s):  
Experimental Data ◽  
Stress Relaxation ◽  
Notch Root ◽  
Hold Time ◽  
Local Stress ◽  
Frequency Effect ◽  
Strengthening Effect ◽  
Strain Accumulation ◽  
Element Analysis ◽  
Creep Fatigue

A study of the notch and frequency effects on fatigue life at high temperature is carried out using notched and unnotched plate specimens of SS 304 under stress-controlled testing conditions. Analysis of the σ-Nf results obtained at 600°C under fatigue and creep-fatigue conditions allowed the generalization of the σ-Nf-Kt relation proposed in an earlier study. Examinations of the experimental data with hold-time testing suggested that in these conditions, the frequency effect should be incorporated in the relationship. Results obtained from the modified relation are in agreement with the experimental data, within a factor of two. Finite element analysis was carried out to determine the state of stresses and strains at the notch root by simulating four creep-fatigue cycles. The computed results indicated that, under zero-to-tension cyclic loading with controlled nominal stress, the maximum local stress at the notch root relaxes; this results in a minimum local stress in compression, and as a consequence, the mean local stress is significantly reduced. The stress relaxation as well as the creep strain accumulation were found to occur only in the vicinity of the notch (within 0.75 mm). The numerical results concerning the local stress relaxation and the time-dependent strain accumulation are used to explain the notch-strengthening effect on life observed in the present study. [S0094-9930(00)00401-7]

Die Attach Adhesion and Void Formation at the Gaas Substrate Interface

1994 ◽  
Vol 356 ◽  
Author(s):  
Nickolaos Strifas ◽  
Aris Christou
Keyword(s):  
Stress Relaxation ◽  
Void Growth ◽  
Thermal Stresses ◽  
Local Stress ◽  
Temperature Cycling ◽  
Void Volume ◽  
Exponential Relationship ◽  
Element Analysis ◽  
Substrate Interface ◽  
Die Attach

AbstractA model is constructed to consider the stresses (analytically and with Finite Element Analysis (MiA)) which result from the thermal mismatch between the die and the substrate. FHA is used to simulate thermal stresses induced from temperature cycling with voids and without voids in the die-attach at the die-substrate interface. Local stress concentration caused by voids is found to be dependent on the location of the voids. The presence of an edge void at the die-attach interface changes the local stress and creates a longitudinal stress field. It is also observed that for die-attachment without voids or some center voids there will be no cracking whereas specimens with voids near the edge of the die are likely to have vertical die cracks. Using the void growth, stress relaxation equations, the void growth is simulated yielding an exponential relationship to void grow th and a saturation of void volume w ith time. Stress relaxation and void growth during cool down are simulated, once the material parameters and cooling rates are known. It yields a time dependence of the relative void volume (exponential decay).

Local and Non-Local Approaches to Fatigue of Weldments: State of the Art and Possible Developments

2007 ◽  
Vol 348-349 ◽  
pp. 529-532
Author(s):  
Roberto Tovo ◽  
Paolo Livieri
Keyword(s):  
Fatigue Strength ◽  
Numerical Methods ◽  
Welded Joints ◽  
State Of The Art ◽  
Local Stress ◽  
Geometrical Model ◽  
Strength Assessment ◽  
Notch Stress ◽  
Non Local ◽  
Stress States

This paper attempts to critically review some numerical methods for fatigue strength assessment of welded joints by means of stress analysis tools (usually FE models). In particular, it focuses on the significance of geometrical model, by distinguishing beams from shells and solids, more than distinguishing among nominal, structural and notch stress type. In addition, basing on continuous mechanics theories, a distinction between “local” and “non-local” stress approaches is proposed. Finally the advantages of notch stress approaches are showed by commenting also problems connected to multiaxiality and three-dimensionality of stress states.

Local stress relaxation phenomena in thin aluminum films

1991 ◽  
Vol 9 (4) ◽  
pp. 2527-2535 ◽  
Author(s):  
Ulf Smith ◽  
Nils Kristensen ◽  
Fredric Ericson ◽  
Jan‐Åke Schweitz
Keyword(s):  
Stress Relaxation ◽  
Local Stress ◽  
Relaxation Phenomena ◽  
Aluminum Films ◽  
Thin Aluminum

Dynamic analysis of two collinear permeable Mode-I cracks in piezoelectric materials based on non-local piezoelectricity theory

2019 ◽  
Vol 15 (6) ◽  
pp. 1274-1293
Author(s):  
Haitao Liu ◽  
Shuai Zhu
Keyword(s):  
Piezoelectric Materials ◽  
Electric Displacement ◽  
Local Stress ◽  
Classical Solutions ◽  
Mode I ◽  
Dual Integral Equations ◽  
Content Type ◽  
Present Solution ◽  
Crack Tips ◽  
Non Local

Purpose Based on the non-local piezoelectricity theory, this paper is concerned with two collinear permeable Mode-I cracks in piezoelectric materials subjected to the harmonic stress wave. The paper aims to discuss this issue. Design/methodology/approach According to the Fourier transformation, the problem is formulated into two pairs of dual integral equations, in which the unknown variables are the displacement jumps across the crack surfaces. Findings Finally, the dynamic non-local stress and the dynamic non-local electric displacement fields near the crack tips are obtained. Numerical results are provided to illustrate the effects of the distance between the two collinear cracks, the lattice parameter and the circular frequency of the incident waves on the entire dynamic fields near the crack tips, which play an important role in designing new structures in engineering. Originality/value Different from the classical solutions, the present solution exhibits no stress and electric displacement singularities at the crack tips in piezoelectric materials. It is found that the maximum stress and maximum electric displacement can be used as a fracture criterion.

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