scholarly journals Mathematical modeling of the fatigue cracks propagation and fatigue life estimation of aluminum structures with slot welds

2021 ◽  
pp. 138-144
Author(s):  
Г.Б. Крыжевич ◽  
А.Р. Филатов
Keyword(s):  
Crack Growth ◽  
High Speed ◽  
Fatigue Cracks ◽  
Equivalent Stress ◽  
Complex Stress ◽  
Complex Stress State ◽  
Tearing Mode ◽  
Joint Influence ◽  
Upper Deck ◽  
Fatigue Life Estimation

Объектом исследования является конструкция верхней палубы соединительного моста высокоскоростного катамарана, выполненного из алюминиевого сплава 1561 (АМг61). Высокая плотность компоновки моста технологически не позволяет выполнять приварку рёбер жёсткости к настилу верхней палубы непрерывным сварным ш вом. Целью работы является расчётная оценка усталостной трещиностойкости конструкции верхней палубы при выполнении сварки прорезным сварным швом. Указанная оценка выполнена на основе эмпирического закона Пэриса – Эрдогана. При этом поскольку конструкция верхней палубы находится в сложном напряжённом состоянии, требуется учёт совместного влияния всех трёх механизмов роста трещин. В результате расчёта получены зависимости длин трещин и коэффициентов интенсивности напряжений от числа циклов нагружения, а также характер роста трещин. Выявлено, что доминирующим механизмом роста трещин является механизм среза, а не отрыва или сдвига. Показано, что прорезные сварные швы могут быть использованы в слабонагруженных алюминиевых конструкциях. The object of research is the structure of the upper deck of the connecting bridge of a high-speed catamaran, made of 1561 (AMg61) aluminum alloy. The high density of the bridge layout technologically does not allow welding of the stiffeners to the upper deck flooring with a continuous weld. The aim of the work is to estimate the fatigue crack resistance of the upper deck structure when welding with a slot weld. The specified estimate is based on the empirical Paris – Erdogan equation. In this case, since the structure of the upper deck is in a complex stress state, it is required to take into account the joint influence of all three mechanisms of crack growth. As a result of the calculation, the dependences of the crack lengths and equivalent stress intensity factors on the number of loading cycles, as well as the nature of crack growth. It has been revealed that the dominant mechanism of crack growth is the tearing mode, not opening or shearing mode. It is shown that slot welds can be used in lightly loaded aluminum structures.

A Practical Criterion on Fatigue Crack Growth Rates at Notches and Its Application to Part-Through-Thickness Fatigue Cracks in Notched Plates Subjected to Cyclic Bending

2006 ◽  
Author(s):  
Hiroshi Matsuno
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Stress Field ◽  
Crack Growth ◽  
Growth Rates ◽  
Fatigue Cracks ◽  
Equivalent Stress ◽  
Cyclic Bending ◽  
Bending Loads ◽  
Crack Growth Rates

In the present paper, an equivalent stress ratio concept, which has hitherto been developed by author [1–3], is applied to problems of part-through-thickness fatigue crack growth in notched plates subjected to cyclic bending loads, and a criterion for estimating fatigue crack growth rates is derived on the basis of the concept. In order to take a great variety of practical notches into consideration, a bending stress field of a notched plate containing a part-through-thickness fatigue crack emanating from a notch root is simplified by the elementary beam theory, and the stress field is characterized in accordance with classification of notch morphology: (a) an unnotch type, (b) a transverse type notch such as a groove, a shoulder, a trapezoidal protuberance, etc., which is disposed along a width of a plate, and (c) a through-thickness type notch such as a circular and elliptical hole, a side-groove, etc. Experimental results on part-through-thickness fatigue cracks emanating from artificial flaws at notch roots in plates subjected to cyclic bending loads are analyzed. Growth rates of fatigue cracks in the notches are estimated based on the proposed criterion and the devised convenient method for calculating stress intensity factors, and they are compared with experimental ones.

Development of a dynamic decohesion criterion for subsonic fracture of the interface between two dissimilar materials

1995 ◽  
Vol 451 (1943) ◽  
pp. 711-736 ◽  
Keyword(s):  
Crack Growth ◽  
High Speed ◽  
Crack Tip ◽  
Dissimilar Materials ◽  
Complex Stress ◽  
High Speed Photography ◽  
Dynamic Crack ◽  
Shear Wave Speed ◽  
Loading Rates ◽  
Lateral Shearing Interferometer

We present findings of an experimental study of dynamic decohesion of bimaterial systems composed of constituents with a large material property mismatch. Poly-methylmethacrylate (PMMA)-steel and PMMA-aluminium bimaterial fracture specimens were used. Dynamic one-point bend loading was accomplished with a drop-weight tower device (for low and intermediate loading rates) or a high-speed gas gun (for high loading rates). High-speed interferometric measurements were made using the lateral shearing interferometer of coherent gradient sensing in conjunction with high-speed photography. Very high crack propagation speeds (terminal crack-tip speeds up to 1.5 c s PMMA , where c s PMMA is the shear wave speed of PMMA) and high accelerations (of about 10 7 g , where g is the acceleration of gravity) were observed and are reported. Issues regarding data analysis of the high-speed interferograms are discussed. The effects of near-tip three-dimensionality are also analysed. Dynamic complex stress factor histories are obtained by fitting the experimental data to available asymptotic crack-tip fields. A dynamic crack growth criterion for crack growth along bimaterial interfaces is proposed. In the subsonic regime of crack growth it is seen that the opening and shearing displacements behind the propagating crack tip remain constant and equal to their value at initiation, i.e. the crack retains a self-similar profile during crack growth at any speed. This forms the basis of the proposed dynamic interfacial fracture criterion.

scholarly journals The Effect of a Complex Stress State on Fatigue Crack Propagation and the Orientation of the Cracking Plane in VT3-1 Aeronautical Titanium Alloy

2009 ◽  
Vol 2009 (1) ◽  
pp. 116-130
Author(s):  
Dorota Kocańda ◽  
Janusz Mierzyński
Keyword(s):  
Titanium Alloy ◽  
Fatigue Crack ◽  
Stress State ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Crack Propagation ◽  
Complex Stress ◽  
Complex Stress State ◽  
Short Crack ◽  
Short Cracks

The Effect of a Complex Stress State on Fatigue Crack Propagation and the Orientation of the Cracking Plane in VT3-1 Aeronautical Titanium AlloyThe subject of the paper is the investigations of fatigue crack imitation and propagation in notched specimens made of the VT3-1 aeronautical russian titanium alloy under combined bending - torsion loading. The presence of short cracks was revealed at various ratios of bending to torsion. Experimental courses of short and long crack growth rates have been proved by the SEM and TEM micrographs which illustrated the changes in the mechanism of cracking in the examined specimens. The attempt was undertaken in order to explain partly brittle fracture that was observed in the range of fatigue short crack growth in the VT3-1 titanium alloy specimens. The results of the study of atmospheric hydrogen absorption capability and its ability for penetration inside the faces of nucleated and propagated microcracks in the surface layer allowed for suggestion that the cleavage mechanism of fracture found in the regime of short crack growth in the VT3-1 titanium alloy specimens was induced by hydrogen.

scholarly journals LOCALIZATION OF PLASTIC DEFORMATION IN COMMERCIALLY PURE TITANIUM IN A COMPLEX STRESS STATE UNDER HIGH-SPEED TENSION

2021 ◽  
pp. 89-102
Author(s):  
V.V. Skripnyak ◽  
◽  
K.V. Iokhim ◽  
V.A. Skripnyak ◽  
◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Stress State ◽  
Strain Rate ◽  
High Speed ◽  
Pure Titanium ◽  
Complex Stress ◽  
Complex Stress State ◽  
Strain Rates ◽  
Commercially Pure Titanium ◽  
Commercially Pure

In this work, the effect of a triaxiality stress state on the mechanical behavior and fracture of commercially pure titanium VT1-0 (Grade 2) in the range of strain rates from 0.1 to 1000 s−1 is studied. Tensile tests are carried out using a servo-hydraulic testing machine Instron VHS 40 / 50-20 on flat specimens with a constant cross-sectional area and on flat specimens with a notch. To study the effect of the complex stress state on the ultimate deformation before fracture, the samples with the notch of various radii (10, 5, 2.5 mm) are used in the experiments. Phantom V711 is employed for high-speed video registration of specimen’s deformation. Deformation fields in a working part of the sample are investigated by the digital image correlation method. It is shown that the effect of the strain rate on the ultimate deformations before fracture has a nonmonotonic behavior. An analysis of strain fields in the working part of the samples shows that the degree of uniform deformation of the working part decreases with an increase in the strain rate. At strain rates above 1000 s−1, the shear bands occur at the onset of a plastic flow. Commercially pure titanium undergoes fracture due to the nucleation, growth, and coalescence of damages in the bands of localized plastic deformation oriented along the maximum shear stresses. The results confirm that the fracture of commercially pure titanium exhibits ductile behavior at strain rates varying from 0.1 to 1000 s−1, at a triaxiality stress parameter in the range of 0.333 ≤ η <0.467, and at a temperature close to 295 K.

Load Spectrum Compiling and Fatigue Life Estimation of the Automobile Wheel Hub

2020 ◽  
Vol 13 ◽  
Author(s):  
Xintian Liu ◽  
Yang Qu ◽  
Xiaobing Yang ◽  
Yongfeng Shen
Keyword(s):  
Fatigue Life ◽  
High Speed ◽  
Two Dimensional ◽  
Load Spectrum ◽  
One Dimensional ◽  
Life Estimation ◽  
Load Spectra ◽  
Fatigue Life Estimation ◽  
Program Load Spectrum ◽  
Program Load

Background:: In the process of high-speed driving, the wheel hub is constantly subjected to the impact load from the ground. Therefore, it is important to estimate the fatigue life of the hub in the design and production process. Objective:: This paper introduces a method to study the fatigue life of car hub based on the road load collected from test site. Methods:: Based on interval analysis, the distribution characteristics of load spectrum are analyzed. The fatigue life estimation of one - dimensional and two - dimensional load spectra is compared by compiling load spectra. Results:: According to the S-N curve cluster and the one-dimensional program load spectrum, the estimated range fatigue life of the hub is 397,100 km to 529,700 km. For unsymmetrical cyclic loading, each level means and amplitude of load were obtained through the Goodman fatigue empirical formula, and then according to S-N curve clusters in the upper and lower curves and two-dimensional program load spectrum, estimates the fatigue life of wheel hub of the interval is 329900 km to 435200 km, than one-dimensional load spectrum fatigue life was reduced by 16.9% - 17.8%. Conclusion:: This paper lays a foundation for the prediction of fatigue life and the bench test of fatigue durability of auto parts subjected to complex and variable random loads. At the same time, the research method can also be used to estimate the fatigue life of other bearing parts or high-speed moving parts and assemblies.

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