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.

Crack Propagation Prediction Using Haensel Damage Model

2012 ◽  
Author(s):  
Piotr Bednarz ◽  
Jaroslaw Szwedowicz
Keyword(s):  
Cyclic Loading ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Damage Model ◽  
Lifetime Prediction ◽  
Dissipated Energy ◽  
Mathematical Approach ◽  
Loading Conditions ◽  
Stored Energy ◽  
Tensile Stresses

The Haensel damage model correlates lifetime of a component until crack initiation to the dissipated and stored energy in the material during cyclic loading. The crack initiation is influenced by mean stresses. The Haensel damage model considers the mean stress effect by including compressive and tensile stresses in calculations of elastic strain energy during cyclic loading conditions. The goal of the paper is to extend the above model to predict crack propagation under large cyclic plasticity and non-proportional loading conditions. After voids initiation onset of necking, voids growth and linking takes place among them. During this process a mesocrack is created. This stage of fracture involves the same amount of released energy for new crack surface creation as dissipated energy for mesocrack initiation. The amount of dissipated and stored energy is related to the process zone size and to the number of cycles. Ilyushin’s postulate is used to calculate the amount of dissipated energy. In order to consider a contribution of tensile stresses only during loading to crack propagation, tensile/compressive split is performed for the stress tensor. One of the key drivers of this paper is to provide a straightforward engineering approach, which does not require explicit modelling of cracks. The proposed mathematical approach accounts for redistribution of stresses, strains and energy during crack propagation. This allows to approximate the observed effect of distribution of dissipated energy on the front of a crack tip. The developed approach is validated through FE (Finite Element) simulations of the Dowling and Begley experiment. The Haensel lifetime prediction of Dowling’s experiment is in good agreement with the experimental data and the explicit FE results. Finally, the proposed mathematical approach simplifies significantly the engineering effort for Nonlinear Fracture Mechanics lifetime prediction by avoiding the requirement to simulate real crack propagation using node base release methods, XFEM or remeshing procedures.

Reduced-thickness CVN testing to represent slant failure of pipelines

2013 ◽  
Vol 4 (1) ◽  
Author(s):  
Jeroen Van Wittenberghe ◽  
Philippe Thibaux ◽  
Patrick Goes
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Propagation Speed ◽  
High Strength ◽  
Dissipated Energy ◽  
Specimen Thickness ◽  
Absorbed Energy ◽  
Element Analysis ◽  
The Difference ◽  
Energy Dissipated

To avoid longitudinal ductile crack propagation along a gas pipeline, the Batelle Two Curve method is used during pipeline design. This method states that a running crack will be arrested if the gas decompression velocity exceeds the crack propagation speed at the internal gas pressure. The crack propagation curve is scaled by impact energy values obtained through Charpy V-Notch (CVN) testing. However, for high-strength steel grades this scaling leads to unconservative predictions, because the experiment does not sufficiently represent the pipeline failure mode. The CVN specimen exhibits mainly mode I failure, without significant shear lips, while real failure is a combined mode often described as slant failure. In the present study, instrumented CVN tests are carried out on samples with different thickness reduction levels. To get a better insight in the crack initiation and propagation behaviour, the CVN test is simulated by finite element analysis. The dissipated energy and resulting fracture surfaces can be successfully represented. It is observed that slant failure is promoted by reducing the specimen thickness. In addition, the specific absorbed energy is decreased. However, most of the difference of absorbed energy is in crack initiation. This means that the fraction of the total energy dissipated in crack propagation is increased for reduced thickness specimens, making it a possible tool to assess the resistance of a material to crack propagation, provided that brittle fracture is avoided.

Modeling Intersonic Crack Propagation in Fiber Reinforced Composites With Contact/Cohesive Laws

2001 ◽  
Author(s):  
S. K. Dwivedi ◽  
H. D. Espinosa
Keyword(s):  
Crack Initiation ◽  
Crack Propagation ◽  
Epoxy Composite ◽  
Dynamic Crack Propagation ◽  
Interface Element ◽  
Dynamic Crack ◽  
Crack Speed ◽  
Interface Elements ◽  
Intersonic Crack Propagation ◽  
The Impact

Abstract Dynamic crack propagation in an unidirectional Carbon/Epoxy composite is studied through finite element analyses in total Lagrangian co-ordinates. A finite deformation anisotropic visco-plastic model is used to describe the constitutive response of the composite. Crack initiation and propagation is simulated by embedding zero thickness interface element along the possible crack path. An irreversible cohesive law is used to describe the evolution of normal and shear tractions as a function of displacement jumps. The compressive response prior to interface failure is analyzed using contact impenetrability conditions. The failure of the first interface element at the pre-notch tip models crack initiation. Crack propagation is modeled through consecutive failure of interface elements. Dynamic crack propagation phenomena are studied in terms of crack initiation time, crack speed, mode I and mode II displacement jumps and tractions associated with the failure of interface elements, effective plastic strain at the crack tip and path independent integral J′. Analyses are first carried out for the dynamic crack propagation along bi-material interfaces. The results obtained from present analyses agree well with literature data. Detailed analyses are carried out for a pre-notched unidirectional Carbon/Epoxy composite material. The impact velocity in the analyses is an imposed velocity over an assumed impact region and remains constant throughout the analysis. Analyses are carried out at impact velocities of 5, 10, 20, 30 and 40 m/s, assuming the crack wake is frictionless. Moreover, analyses at impact velocities of 30 and 40 m/s are also carried out with a friction coefficient of 0.5 along the crack surfaces. The analyses established intersonic crack speed in the fiber reinforced composite material. Intersonic crack propagation for the impact velocities of 40 m/s is 400% of the shear wave speed and 87% of the longitudinal wave speed. Detailed discussion is given on the features of sub-sonic and intersonic crack propagation in Carbon/Epoxy composite materials. It is shown that the friction coefficient along the crack surface plays an important role by smearing the discontinuous field that develops behind the crack tip and by reducing crack speed in the intersonic regime. The analyses show that the contour integral J′ computed at near field contours are path independent and can serve as a parameter for characterizing intersonic crack propagation.

scholarly journals Computer Simulation of Car Aerodynamic Properties

2017 ◽  
Vol 65 (5) ◽  
pp. 1505-1514 ◽  
Author(s):  
Ivan Janoško ◽  
Tomáš Polonec ◽  
Peter Kuchar ◽  
Pavel Máchal ◽  
Martin Zach
Keyword(s):  
Rear Axle ◽  
Aerodynamic Drag ◽  
Aerodynamic Characteristics ◽  
Front Axle ◽  
Simulation Software ◽  
The Body ◽  
Body Parts ◽  
Aerodynamic Properties ◽  
Before And After ◽  
The Impact

The paper presents an optimization of car aerodynamic properties using the simulation software STAR‑CCM+. For real simulation was used tested car Fiat 127 which was modified on the performance car. The basic objective of this work is using computer simulations to obtain knowledge about the impact of individual body parts on the results of aerodynamic drag, downforce or lift. Based on the results, bodywork modifications will be designed to improve the aerodynamic characteristics of the body, but would not disrupt the basic shape and appearance of the vehicle. The modifications will be again subjected to tests in simulation software. On the modified body was significantly reduced torque of the front axle, while increased of rear axle (cca 1250 N.m). This caused a significant stabilizing effect on the rear axle. The results of simulation tests before and after use bodywork modifications are processed in graphical and numerical form.

Strategic Role of Zakat in Multidimensional Quality of Life in Sijunjung, Indonesia

2018 ◽  
Vol 15 (1) ◽  
pp. 55-72
Author(s):  
Herlin Hamimi ◽  
Abdul Ghafar Ismail ◽  
Muhammad Hasbi Zaenal
Keyword(s):  
Quality Of Life ◽  
Positive Impact ◽  
Wealth Distribution ◽  
Absolute Poverty ◽  
Before And After ◽  
The Status ◽  
Being There ◽  
The Impact

Zakat is one of the five pillars of Islam which has a function of faith, social and economic functions. Muslims who can pay zakat are required to give at least 2.5 per cent of their wealth. The problem of poverty prevalent in disadvantaged regions because of the difficulty of access to information and communication led to a gap that is so high in wealth and resources. The instrument of zakat provides a paradigm in the achievement of equitable wealth distribution and healthy circulation. Zakat potentially offers a better life and improves the quality of human being. There is a human quality improvement not only in economic terms but also in spiritual terms such as improving religiousity. This study aims to examine the role of zakat to alleviate humanitarian issues in disadvantaged regions such as Sijunjung, one of zakat beneficiaries and impoverished areas in Indonesia. The researcher attempted a Cibest method to capture the impact of zakat beneficiaries before and after becoming a member of Zakat Community Development (ZCD) Program in material and spiritual value. The overall analysis shows that zakat has a positive impact on disadvantaged regions development and enhance the quality of life of the community. There is an improvement in the average of mustahik household incomes after becoming a member of ZCD Program. Cibest model demonstrates that material, spiritual, and absolute poverty index decreased by 10, 5, and 6 per cent. Meanwhile, the welfare index is increased by 21 per cent. These findings have significant implications for developing the quality of life in disadvantaged regions in Sijunjung. Therefore, zakat is one of the instruments to change the status of disadvantaged areas to be equivalent to other areas.

ANALISIS PENGARUH PEMBANGUNAN JALAN LAYANG JANTI TERHADAP PERKEMBANGAN TATA RUANG KAWASAN JANTI STUDI KASUS : KAWASAN JANTI, DESA CATURTUNGGAL, KABUPATEN SLEMAN, D. I. YOGYAKARTA

2017 ◽  
Vol 11 (3) ◽  
pp. 255
Author(s):  
Jeky El Boru
Keyword(s):  
Road Network ◽  
Open Space ◽  
Qualitative Description ◽  
Analysis Method ◽  
Open Spaces ◽  
The Road ◽  
Before And After ◽  
Linkage Method ◽  
The Impact ◽  
Parking Place

Abstract: This research aims to analyze the impact of Janti Flyover Construction toward the growth of layout at Janti Urban Area, including structured space, open space, and linkage. Method used for data collecting are observation, air photograph monitoring, and interview, whereas the analysis method is qualitative description, which is the superimposed method of two layers, that are the layout condition before and after flyover construction. The result shows that the impact of Janti Flyover construction can be seen on building mass (solid), the increasing number of open spaces, including the road network, parking place, and park, whereas the relation between spaces, visually and structurally, can be seen on the growth of buildings which have new shapes and styles, therefore the performance of the overall building does not have a proportional shape. Considering Janti Street at the collective relation, its role is getting stronger as the main frame road network.Keywords: Flyover construction, layout changing, Janti AreaAbstrak: Penelitian ini bertujuan untuk menganalisis pengaruh pembangunan Jalan Layang Janti terhadap perkembangan tata ruang Kawasan Janti, meliputi ruang terbangun, ruang terbuka, serta hubungan antar ruang (“linkage”). Metode pengumpulan data dilakukan melalui observasi, pengamatan foto udara, dan wawancara; sedangkan metode analisis melalui deskripsi secara kualitatif yang berupa “superimposed method” dari dua lapisan kondisi lahan, yakni kondisi tata ruang sebelum dan sesudah pembangunan jalan layang. Hasil penelitian menunjukkan bahwa pengaruh pembangunan Jalan Layang Janti terdapat pada massa bangunan (“solid”), pertambahan ruang terbuka yang berupa jaringan jalan, parkir, dan taman; sedangkan pada hubungan antar ruang ̶ secara visual dan struktural ̶ yakni tumbuhnya bangunan dengan bentuk dan gaya baru, sehingga bentuk tampilan bangunan secara keseluruhan tidak proporsional. Pada hubungan kolektif, Jalan Janti semakin kuat perannya sebagai kerangka utama jaringan jalan.Kata kunci : Pembangunan jalan layang, tata ruang, Kawasan Janti

Impact of merger on efficiency and productivity : a case study of commercial banks in Malaysia

1970 ◽  
Vol 5 (1) ◽  
pp. 77
Author(s):  
Mahadzir Ismail ◽  
Saliza Sulaiman ◽  
Hasni Abdul Rahim ◽  
Nordiana Nordin
Keyword(s):  
Efficiency Score ◽  
Malmquist Productivity Index ◽  
Productivity Index ◽  
Data Envelopment ◽  
Master Plan ◽  
Before And After ◽  
Domestic Banks ◽  
The Impact ◽  
Efficiency And Productivity

The Financial Master Plan (2001- 2010) aims to enhance the capacity of banking industry so that higher effic iency and productivity can be reaped in the future. This study seeks to determine the impact of merger on the efficiency and productivity ofcommercial banks in Malaysia for the period 1995 until 2005. The study uses a non-parametric approach, nam ely DEA (data envelopment analysis?) to estimate the efficiency scores and to construct the Malmquist productivity index. To enable this estimation, three bank inputs and outputs are used. Amongst the findings are those banks exhibit higher efficiency score after the merger and thefo reign banks are more efficient than the local banks. Productivity of the banks is calculated in both periods, before and after the merger: The results show that, it is the local banks that have improved the most after the merger. The main source of productivity is technical change or innovation. The findings support the existing policy of having larger domestic banks in term of size.

THE EFFECT OF METACOGNITIVE INSTRUCTION ON MAXIMIZING EFL LEARNERS’ METACOGNITIVE AWARENESS IN LISTENING

2018 ◽  
Vol 7 (1) ◽  
pp. 8-17
Author(s):  
Mahsa Assadi
Keyword(s):  
Experimental Research ◽  
Listening Comprehension ◽  
Intervention Program ◽  
Metacognitive Awareness ◽  
Listening Test ◽  
Efl Learners ◽  
Metacognitive Instruction ◽  
Before And After ◽  
Comprehension Ability ◽  
The Impact

This study reports a pre-experimental research on the impact of metacognitive instruction on EFL learners’ metacognitive awareness and their listening performance. To obtain the goal of the study, a group of 30 Iranian intermediate EFL learners, including 14 males and 16 females, were selected randomly. Their ages range from 20 to 24. The participants took part in 16 weeks’ intervention program based on metacognitive pedagogical sequence consisted of five stages. The metacognitive awareness listening questionnaire (MALQ), and a listening test were also used to find changes in metacognitive awareness and listening performance before and after the treatment. The results of comparing pre and posttests scores revealed that metacognitive instruction raised the learners’ metacognitive awareness and helped them improve their listening comprehension ability.

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