Fracture toughness and failure mechanisms in un-vulcanized and dynamically vulcanized PP/EPDM/MWCNT blend-nanocomposites

RSC Advances ◽  
2015 ◽  
Vol 5 (87) ◽  
pp. 70817-70831 ◽  
Author(s):  
Mehrdad Khodabandelou ◽  
Mir Karim Razavi Aghjeh ◽  
Majid Mehrabi Mazidi
Keyword(s):  
Fracture Toughness ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Failure Mechanisms ◽  
The Individual ◽  
P Addition ◽  
Blend Nanocomposites

Addition of MWCNTs into the PP/EPDM blend reduced the we and enhanced the βwp. In the blend-nanocomposites large MWCNT aggregates acted as favored sites for crack initiation, and the individual MWCNT impregnated fibrils arrested the crack propagation.

Failure Behaviour of High Toughness Multi-Layer Si3N4 and Si3N4-TiN Based Laminates

2005 ◽  
Vol 290 ◽  
pp. 175-182 ◽  
Author(s):  
Gurdial Blugan ◽  
Richard Dobedoe ◽  
I. Gee ◽  
Nina Orlovskaya ◽  
Jakob Kübler
Keyword(s):  
Fracture Toughness ◽  
High Temperature ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Failure Mechanisms ◽  
High Strength ◽  
Crack Deflection ◽  
High Toughness ◽  
Energy Absorbing ◽  
Crack Bifurcation

Multi-layer laminates were produced using alternating layers of Si3N4 and Si3N4+TiN. The differences in the coefficient of thermal expansions between the alternating layers lead to residual stresses after cooling. These are compressive in the Si3N4 layers and tensile in the Si3N4+TiN layers. The existence of these stresses in the laminates effect the crack propagation behaviour during failure. Different designs of laminates were produced with external layers under compression and tension exhibiting different failure mechanisms. Facture toughness was measured by SEVNB method. In systems with external layers under compression the measured fracture toughness was up to three times that of Si3N4, i.e. up to 17 MPa m1/2. In systems with external layers under tension during failure the energy absorbing effects of crack deflection and crack bifurcation were obtained. High temperature tests were performed to determine the onset temperature for residual stresses in these laminates. Micro-laminates with compressive layers of only 30 µm thickness with high strength and fracture toughness and were manufactured.

Relationships Between Microstructure and Engineering Properties

1986 ◽  
Vol 85 ◽  
Author(s):  
P. L. Pratt
Keyword(s):  
Fracture Toughness ◽  
Compressive Strength ◽  
Elastic Modulus ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Realistic Model ◽  
Engineering Properties ◽  
Bend Strength ◽  
Cement Pastes ◽  
Complex Models

ABSTRACTThe calculation of such macroscopic engineering properties as elastic modulus and compressive strength for cement pastes and concrete depends upon the establishment of a realistic model of the microstructure. Increasingly complex models are considered, which appear capable of predicting the elastic modulus in terms of a modified Rule of Mixtures. The same models are able to account for the broad features of the compressive strength, because strength is always scaled by the elastic modulus of the material. The actual value of the compressive or the bend strength is determined by the mechanics of crack initiation and crack propagation in the particular test used. Crack initiation is controlled by the defects present in the material and crack propagation by the fracture toughness of the different phases and the porosity in the microstructure. Thus the strength depends upon microstructure in a number of different but interrelated ways, determined by the fracture toughness of the material.

On the Failure Mechanisms in Reactor Pressure Vessel with Austenitic Cladding

2015 ◽  
Vol 784 ◽  
pp. 492-499
Author(s):  
Jan Štefan ◽  
Jan Siegl ◽  
Miloš Kytka ◽  
Milan Brumovský
Keyword(s):  
Fracture Toughness ◽  
Crack Propagation ◽  
Neutron Irradiation ◽  
Pressure Vessel ◽  
Failure Mechanisms ◽  
Reactor Pressure Vessel ◽  
Fractographic Analysis ◽  
The Relationship ◽  
Reactor Pressure

The austenitic cladding of the WWER pressure vessel is made from two different layers with different fracture toughness values. Based on the fractographic analysis of the tested specimens in the initial, as well as in the irradiated conditions, it was found that individual failure micromechanisms take place during the crack propagation. The obtained results were used to find the relationship between the failure micromechanism changes and the fracture toughness values, as well as to assess the effect of neutron irradiation on the failure micromechanisms.

Fracture toughness assessment at different regions in an inertial friction welded Ti-5Al-2Sn-2Zr-4Mo-4Cr alloy plate

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Yingping Ji ◽  
Sujun Wu
Keyword(s):  
Fracture Toughness ◽  
Crack Propagation ◽  
Parent Material ◽  
Propagation Path ◽  
Crack Tip Opening Displacement ◽  
Opening Displacement ◽  
Alloy Plate ◽  
Temperature Fracture ◽  
The Individual ◽  
Crack Tip Opening

Abstract The study aims to ascertain the influences of position on fracture toughness and fracture mechanism of inertial friction welded Ti-5Al-2Sn-2Zr-4Mo-4Cr joints. The room-temperature fracture toughness values of the parent material and three other regions in the weld were evaluated by standard crack tip opening displacement tests. The micro-structure and tensile properties of the welds were also investigated. Based on the observation of fracture surface and crack propagation path, a schematic illustration of the crack propagation was formed. The results suggest that the weld metal had the worst fracture toughness. The individual fracture toughness of different regions in the weld could be explained by the various modes of crack propagation, which were affected by different microstructures.

scholarly journals Experimental and Numerical Study of Fracture Behavior of Rock-Like Material Specimens with Single Pre-Set Joint under Dynamic Loading

Materials ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2690
Author(s):  
Bo Pan ◽  
Xuguang Wang ◽  
Zhenyang Xu ◽  
Lianjun Guo ◽  
Xuesong Wang
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Joint Angle ◽  
Simulation Software ◽  
Dissipated Energy ◽  
Energy Structure ◽  
Joint Angles ◽  
Crack Penetration ◽  
Before And After ◽  
The Impact

The Split Hopkinson Pressure Bar (SHPB) is an apparatus for testing the dynamic stress-strain response of the cement mortar specimen with pre-set joints at different angles to explore the influence of joint attitudes of underground rock engineering on the failure characteristics of rock mass structure. The nuclear magnetic resonance (NMR) has also been used to measure the pore distribution and internal cracks of the specimen before and after the testing. In combination with numerical analysis, the paper systematically discusses the influence of joint angles on the failure mode of rock-like materials from three aspects of energy dissipation, microscopic damage, and stress field characteristics. The result indicates that the impact energy structure of the SHPB is greatly affected by the pre-set joint angle of the specimen. With the joint angle increasing, the proportion of reflected energy moves in fluctuation, while the ratio of transmitted energy to dissipated energy varies from one to the other. NMR analysis reveals the structural variation of the pores in those cement specimens before and after the impact. Crack propagation direction is correlated with pre-set joint angles of the specimens. With the increase of the pre-set joint angles, the crack initiation angle decreases gradually. When the joint angles are around 30°–75°, the specimens develop obvious cracks. The crushing process of the specimens is simulated by LS-DYNA software. It is concluded that the stresses at the crack initiation time are concentrated between 20 and 40 MPa. The instantaneous stress curve first increases and then decreases with crack propagation, peaking at different times under various joint angles; but most of them occur when the crack penetration ratio reaches 80–90%. With the increment of joint angles in specimens through the simulation software, the changing trend of peak stress is consistent with the test results.

scholarly journals Crack Propagation in the Tibia Bone within Total Knee Replacement Using the eXtended Finite Element Method

2021 ◽  
Vol 11 (10) ◽  
pp. 4435
Author(s):  
Ho-Quang NGUYEN ◽  
Trieu-Nhat-Thanh NGUYEN ◽  
Thinh-Quy-Duc PHAM ◽  
Van-Dung NGUYEN ◽  
Xuan Van TRAN ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Fracture Prevention ◽  
Patient Specific ◽  
Extended Finite Element ◽  
Tibia Bone ◽  
Age Related ◽  
Final Failure

Understanding of fracture mechanics of the human knee structures within total knee replacement (TKR) allows a better decision support for bone fracture prevention. Numerous studies addressed these complex injuries involving the femur bones but the full macro-crack propagation from crack initiation to final failure and age-related effects on the tibia bone were not extensively studied. The present study aimed to develop a patient-specific model of the human tibia bone and the associated TKR implant, to study fatigue and fracture behaviors under physiological and pathological (i.e., age-related effect) conditions. Computed tomography (CT) data were used to develop a patient-specific computational model of the human tibia bone (cortical and cancellous) and associated implants. First, segmentation and 3D-reconstruction of the geometrical models of the tibia and implant were performed. Then, meshes were generated. The locations of crack initiation were identified using the clinical observation and the fatigue crack initiation model. Then, the propagation of the crack in the bone until final failure was investigated using the eXtended finite element method (X-FEM). Finally, the obtained outcomes were analyzed and evaluated to investigate the age-effects on the crack propagation behaviors of the bone. For fatigue crack initiation analysis, the stress amplitude–life S–N curve witnessed a decrease with increasing age. The maximal stress concentration caused by cyclic loading resulted in the weakening of the tibia bone under TKR. For fatigue crack propagation analysis, regarding simulation with the implant, the stress intensity factorand the energy release rate tended to decrease, as compared to the tibia model without the implant, from 0.152.5 to 0.111.9 (MPa) and from 10240 to 5133 (J), respectively. This led to the drop in crack propagation speed. This study provided, for the first time, a detailed view on the full crack path from crack initiation to final failure of the tibia bone within the TKR implant. The obtained outcomes also suggested that age (i.e., bone strength) also plays an important role in tibia crack and bone fracture. In perspective, patient-specific bone properties and dynamic loadings (e.g., during walking or running) are incorporated to provide objective and quantitative indicators for crack and fracture prevention, during daily activities.

Modeling of Fatigue Crack Propagation

2004 ◽  
Vol 126 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Yanyao Jiang ◽  
Miaolin Feng
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Fatigue Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Cyclic Plasticity ◽  
R Ratio

Fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants for crack initiation. The cyclic elastic-plastic stress-strain field near the crack tip was analyzed using the finite element method with the implementation of a robust cyclic plasticity theory. An incremental multiaxial fatigue criterion was employed to determine the fatigue damage. A straightforward method was developed to determine the fatigue crack growth rate. Crack propagation behavior of a material was obtained without any additional assumptions or fitting. Benchmark Mode I fatigue crack growth experiments were conducted using 1070 steel at room temperature. The approach developed was able to quantitatively capture all the important fatigue crack propagation behaviors including the overload and the R-ratio effects on crack propagation and threshold. The models provide a new perspective for the R-ratio effects. The results support the notion that the fatigue crack initiation and propagation behaviors are governed by the same fatigue damage mechanisms. Crack growth can be treated as a process of continuous crack nucleation.

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