Experimental Study on Mechanism of Crack Coalescence between Two Pre-Existing Flaws under Dynamic Loading

2006 ◽  
Vol 324-325 ◽  
pp. 117-120 ◽  
Author(s):  
Ping Zhang ◽  
Ning Li ◽  
Ruo Lan He
Keyword(s):  
Crack Propagation ◽  
Dynamic Loading ◽  
Static Loading ◽  
Crack Coalescence ◽  
Engineering Practice ◽  
Strength Increase ◽  
Strain Rates ◽  
Inertia Effect ◽  
Coalescence Pattern ◽  
Static And Dynamic Loading

More and more engineering practice indicates rock mass is prone to lose its stability through crack coalescence under dynamic loading, such as blasting and earthquake. However, the crack coalescence pattern of rock specimens containing two or more flaws has not been studied comprehensively under dynamic loading. In this paper, the mechanism of the crack coalescence and peak strength of sandstone-like materials containing two parallel flaws are studied under uniaxial static and dynamic loading with strain rates 1.7×10-5 s-1 and 1.7×10-1 s-1. Through the comparisons of the propagation length, coalescence pattern of the cracks and strength increase of the pre-cracked specimens under static and dynamic loading, the dynamic response of the crack coalescence is found different from static loading under different geometric setting of the flaws. The inertia effect of the crack propagation is revealed under dynamic loading, that is to say, the growth of the secondary cracks tends to the original propagation direction, and the direct and immediate coalescence is taken place easily between two pre-existing flaws, which is different from the kinking coalescence under static loading. So, the inertia effect of the crack propagation is regarded as the main cause of the strength increase of the brittle material under dynamic loading for medium strain rates. In virtue of the explanation, another cause of the mode II shear fracture occurred under earthquake is opened out.

Response of Silica-Nylon6 Nanocomposites to Static and Dynamic Loading

2012 ◽  
Vol 706-709 ◽  
pp. 786-792
Author(s):  
V.P.W. Shim ◽  
Y.B. Guo ◽  
H. W. Gu ◽  
Xu Li
Keyword(s):  
Dynamic Loading ◽  
Static Loading ◽  
Silica Nanoparticle ◽  
Particle Dispersion ◽  
Type B ◽  
Dynamic Tension ◽  
Range Interaction ◽  
Covalent Bonds ◽  
Long Range Interaction ◽  
Static And Dynamic Loading

Silica-nylon6 composites were fabricated using two types of silica nanoparticle fillers with different surface modifications. Type A particles (treated with hexamethyldisilazane) were uniformly dispersed but only displayed weak long-range interaction with the nylon6 matrix; in contrast, type B particles (modified with 3-aminopropyltriethoxysilane) formed covalent bonds with the nylon6 chains but their dispersion is not good. The silica-nylon6 composites synthesized were subjected to quasi-static and dynamic tension to study the effects of strain rate and nanoparticle fraction. Results show that compared to quasi-static loading, both pure nylon6 and the composites exhibit a higher strength but lower ductility under dynamic loading. With respect to the influence of the nanoparticles, both particle types cause an increase in the elastic modulus and tensile strength. The effect of the two particles on ductility differs – particle A reduces ductility, while particle B decreases ductility under quasi-static loading but enhances it noticeably for dynamic loading. Particle B enhances the mechanical properties more significantly, especially in terms of ductility. These results suggest that ensuring strong particle-matrix bonding is more crucial than good particle dispersion.

scholarly journals What is the influence of two strain rates on the relationship between human cortical bone toughness and micro-structure?

2019 ◽  
Vol 234 (3) ◽  
pp. 247-254 ◽  
Author(s):  
Rémy Gauthier ◽  
Hélène Follet ◽  
Max Langer ◽  
Françoise Peyrin ◽  
David Mitton
Keyword(s):  
Crack Propagation ◽  
Strain Rate ◽  
Cortical Bone ◽  
Static Loading ◽  
Fracture Mechanisms ◽  
Strain Rates ◽  
Micro Structure ◽  
Human Cortical Bone ◽  
Cross Links ◽  
Haversian System

Cortical bone fracture mechanisms are well studied under quasi-static loading. The influence of strain rate on crack propagation mechanisms needs to be better understood, however. We have previously shown that several aspects of the bone micro-structure are involved in crack propagation, such as the complete porosity network, including the Haversian system and the lacunar network, as well as biochemical aspects, such as the maturity of collagen cross-links. The aim of this study is to investigate the influence of strain rate on the toughness of human cortical bone with respect to its microstructure and organic non-collagenous composition. Two strain rates will be considered: quasi-static loading (10−4 s−1), a standard condition, and a higher loading rate (10−1 s−1), representative of a fall. Cortical bone samples were extracted from eight female donors (age 50–91 years). Three-point bending tests were performed until failure. Synchrotron radiation micro-computed tomography imaging was performed to assess bone microstructure including the Haversian system and the lacunar system. Collagen enzymatic cross-link maturation was measured using a high performance liquid chromatography column. Results showed that that under quasi-static loading, the elastic contribution of the fracture process is correlated to both the collagen cross-links maturation and the microstructure, while the plastic contribution is correlated only to the porosity network. Under fall-like loading, bone organization appears to be less linked to crack propagation.

scholarly journals COMPARISON OF NECK MUSCLE ELECTROMYOGRAPHY ACTIVITY IN RESPONSE TO EXTERNAL FORCE BETWEEN STATIC AND DYNAMIC LOADING

2019 ◽  
Vol 19 (04) ◽  
pp. 1850034
Author(s):  
D. W. KAK ◽  
A. R. ANITA ◽  
N. M. NIZLAN ◽  
I. NORMALA ◽  
N. A. ABDUL JALIL ◽  
...  
Keyword(s):  
Dynamic Loading ◽  
Static Loading ◽  
Muscle Activation ◽  
Motor Vehicle ◽  
Neck Muscles ◽  
Motor Vehicle Crash ◽  
Neck Muscle ◽  
Activation Level ◽  
Static And Dynamic Loading ◽  
Head Neck

Understanding the behavior of neck muscles is essential to accurately simulate the human head-neck segment movement especially for low-speed motor vehicle crash situation. Some head-neck mathematical models were designed using neck muscle activation behavior in isometric contraction (static loading) as the properties of neck muscle activation. However, neck muscle activation pattern and strength capability may vary between static and dynamic loading. This study aimed to determine the differences between neck muscle activation level under static and dynamic loading. A neck strength test involving 22 human volunteers was conducted with two different tasks in extension and flexion direction with three different loads. The neck muscle activation level is determined through measuring the electromyography (EMG) responses of selected flexor and extensor muscles using surface bilateral electrode and recorded. The findings showed that neck muscle activation level was significantly greater in dynamic loading than static loading ([Formula: see text]). These implied that more efforts from neck muscles were required to resist against dynamic loading than static loading. Nonetheless, the differences in EMG activities between these two loading conditions progressively decreased when more loads were applied. This study has established an empirical model to describe the relationship between neck muscle activation level and force output for both loading condition in flexion and extension.

STUDY OF CHARACTERISTICS OF MECHANICAL PROPERTIES OF GAS-DISTRIBUTING STATION PIPES METAL AFTER LONG-TERM OPERATION

2015 ◽  
pp. 86-91
Author(s):  
I. Yu. Bykov ◽  
I. N. Birillo ◽  
P. A. Kuzbozhev
Keyword(s):  
Mechanical Properties ◽  
High Pressure ◽  
Internal Pressure ◽  
Dynamic Loading ◽  
Static Loading ◽  
High Speed ◽  
Term Operation ◽  
Loading Effects ◽  
Static And Dynamic Loading

During operation the technological pipelines of gas-distributing station are affected by mechanical static loading resulted from internal pressure of gas in the high pressure pipelines and a dynamic loading from a high-speed stream of gas in low pressure pipelines. A comparison is made of characteristics of mechanical properties of gas-distributing station pipes metal after a long-term operation for the conditions of static and dynamic loading effects.

scholarly journals Experimental Investigations on Pullout Behavior of HDPE Geogrid under Static and Dynamic Loading

2020 ◽  
Vol 2020 ◽  
pp. 1-13
Author(s):  
Zheng Zuo ◽  
Guangqing Yang ◽  
He Wang ◽  
Zhijie Wang
Keyword(s):  
Dynamic Loading ◽  
Static Loading ◽  
Coarse Sand ◽  
Reinforced Soil ◽  
Growth Patterns ◽  
Experimental Investigations ◽  
Pullout Resistance ◽  
Pullout Tests ◽  
Soil Structures ◽  
Static And Dynamic Loading

This paper describes a series of laboratory pullout tests that were performed to investigate the pullout behavior of high-density polyethylene (HDPE) uniaxial geogrid subjected to static and dynamic loading. Pullout tests were conducted on HDPE geogrid reinforced coarse sand under normal static loading (60–300 kPa), dynamic loading with different amplitudes (20, 40, and 60 kPa), and different frequencies (2, 4, and 6 Hz) by using the newly developed pullout apparatus. The results indicated that the pullout resistance of geogrid presented different growth patterns with the increase of normal loads under static loading. The amplitude and frequency both had significant effects on the interaction between reinforcement and soil, and the increment of the pullout resistance was 0.6 kN and 0.3 kN, respectively. The effect of dynamic loading on the soil-geogrid interface can be gradually equivalent to that of static loading corresponding to the balance position of dynamic loading with the increase of frequency compared with the static loading. The results of this study are helpful for the selection of the strength of the reinforcement in different locations and to simplify the study on the stress of reinforcement in reinforced soil structures under traffic loads.

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