Explosive Fracture Research Articles

Explosive stress wave propagation and fracture characteristics of rock-like materials with weak filling defects

Filling-type defects have a non-negligible effect on the propagation of explosive stress waves in rock. Combined with the new dynamic caustics experimental system and ANSYS/LS-DYNA numerical simulation platform, the research on the propagation characteristics of explosive stress wave and fracture characteristics of rock-like materials containing weak filling defects with different ductility has been carried out. Firstly, we analyzed the influence of weak filling on the propagation of blast-induced cracks, explored the “guiding” and “stopping” effects of weak filling on cracks, and analyzed the mechanical characteristics of crack propagation. Secondly, the effect of planar weak filling ductility on the damage degree of blasted medium was quantitatively evaluated. Thirdly, the influence of weak filling on the fluctuation characteristics of explosive stress wave was investigated. Then, the mechanical response behavior of the specimens was analyzed, and the results showed that the compaction and slip behaviour characteristics of the weak filling have some variability in degree, some continuity in time, some correlation in space and are affected by the ductility of the planar weak filling. In addition, the stress wave and weak filling interaction mechanism was elucidated. The conclusions of the analysis have positive reference value for understanding the explosion mechanics mechanism of defective rock masses.

Parametric evolutions of explosive fracture zones in the explosion of series of blasthole charges with a complex structure

The purpose of the paper is to specify calculations of a rock mass fracture zone in the explosion of series of blasthole charges with a complex structure under mathematical modelling of their interaction if parts of the blasting agent are spaced along the well length by means of an inert material. The parts are blasted sequentially. Therefore, dynamic load of exploded rock mass has been analyzed depending upon a blasting order of the charges and their parts. Originality is to define more exactly the regularities of interaction between explosive energy of blasthole charges with the specific design and rock mass enclosing them. The developed methods help identify usability of the explosives, designed by the authors, and simplify calculations of drilling-and-blasting description. It has been proved that selection of charge mass with different ratios of their parts in the sequential wells, and variation in lag intervals between the explosions make it possible to control a process of rock mass loading depending upon the specific mining and geological conditions if features of a force field are known. The findings expand methodological basis as for design of open pits while favouring implementation of explosive charges which structure is proposed by the authors.

Damage evolution in flax fibre composite under creep load

This work aims to reveal the damage mechanisms and evolution in unidirectional flax fibre biocomposites when subjected to creep load. X-ray micro computed tomography and acoustic emission (AE) was used to monitor the failure progress during flexural creep tests. A correlation between the event clusters and directly observed damage modes was established based on coupons with expected failure mechanisms and then validated by computed tomography observations. The damage initiated from matrix cracking in the primary creep stage, and then fibre–matrix interface debonding combined with fibre pull-out occurred sequentially during the steady creep stage. In the tertiary creep stage, the explosive fibre fracture emerged and eventually triggered catastrophic failure. Considerably more AE events were detected during creep tests compared to those in quasi-static tests, which indicates that intensive damage is generated under creep load, and therefore causes the strength degradation. A good agreement was observed between the cumulative number of AE events and the increasing damage volume fraction over time determined by X-ray micro computed tomography during multi-step creep tests.

Investigation of dynamic crack formation mechanism based on a new crack dynamic driving model

To reveal the dynamic cracking process of deep rock caused by explosive initiation, the mechanical process of rock cracking is theoretically analyzed firstly under the combined action of explosion stress wave and geostress stress. A new crack dynamic driving model (CDD Model) based on the combined coupling effect is established. The feasibility and rationality of it in characterizing the dynamic cracking process are verified with numerical simulation and laboratory test. And the influence of ground stress on dynamic cracking process of presplitting blasting is revealed. The findings show that the dynamic cracking process of presplitting blasting is affected by explosion stress wave, explosive gas pressure, and ground stress. The opening of explosion crack shows a dynamic changing process of first increasing, then decreasing, and finally increasing. For conventional presplitting blasting, when the initial geostress level exceeds 10 ∼ 20 MPa, the stress transient unloading on fracture surface easily leads to the reduction of the explosive fracture opening. And the possibility of secondary opening and expansion of the explosive fracture is reduced. It will limit the driving effect of the subsequent explosion energy on the fracture expansion.

Mechanical characterization and fractographic study of the carbon/PEI composite under static and fatigue loading

The fatigue life of carbon fiber reinforced thermoplastic matrix composites is of great interest for many engineering applications. This work evaluated the influence of poly(etherimide) (PEI) on the fatigue life of laminated thermoplastic composites reinforced with carbon fibers. The mechanical characterization of the carbon/PEI composites was performed by static loading (tensile test) and cyclic fatigue. Tensile strength obtained was used to calculate 5 stress levels for cyclic fatigue testing with R = 0.1 and 12 Hz for 85, 80, 70, 60, and 55%, being this last stress level found as the infinite life. These stress levels allowed plotting a well-described SN curve. Seeking to understand the fracture behavior of carbon/PEI composites, a fractographic study by scanning electron microscopy (SEM) was performed. SEM micrographs confirm the good quality of carbon/PEI laminate with good adhesion between fibers and matrix and also confirmed the nature of fatigue life showing in-plane fracture for high loads and explosive fracture for lower loads.

Numerical Simulation Study of Expanding Fracture of 45 Steel Cylindrical Shell under Different Detonation Pressure.

Detonation and fragmentation of ductile cylindrical metal shells is a complicated physical phenomenon of material and structural fracture under a high strain rate and high-speed impact. In this article, the smoothed particle hydrodynamics (SPH) numerical model is adopted to study this problem. The model’s reliability is initially tested by comparing the simulation findings with experimental data, and it shows that different fracture modes of cylindrical shells can be obtained by using the same model with a unified constitutive model and failure parameters. By using this model to analyze the explosive fracture process of the cylindrical shells at various detonation pressures, it shows that when the detonation pressure decreases, the cylindrical metal shell fracture changes from a pure shear to tensile–shear mixed fracture. When the detonation pressure is above 31 GPA, a pure shear fracture appears in the shell during the loading stage of shell expansion, and the crack has an angle of 45° or 135° from the radial direction. When the pressure is reduced to 23 GPA, the fracture mode changes to tension–shear mixing, and the proportion of tensile cracks is about one-sixth of the shell fracture. With the explosion pressure reduced to 13 GPA, the proportion of tensile cracks is increased to about one-half of the shell fracture. Finally, the failure mechanism of the different fracture modes was analyzed under different detonation pressures by studying the stress and strain curves in the shells.

Порівняльний аналіз показників при фізичному та математичному моделюванні вибухового перелому грудопоперекового відділу хребта

У наукових дослідженнях для складних систем біомеханіки широко застосованим методом чисельного моделювання є метод кінцевих елементів. Після створення нових математичних моделей із використанням даного методу потребується підтвердження адекватності отриманих результатів, найчастіше для цього проводять їх порівняння з експериментальними (фізичними) моделями. Мета дослідження — побудувати математичні біомеханічні моделі вибухового перелому тіла хребця ThXII та провести їх порівняльний аналіз з експериментальними моделями. За основу моделі була взята експериментальна модель хребців ThIX-LV тварини (свині) та моделі руйнування тіла хребця ThXII, розроблені у лабораторії біомеханіки ДУ «ІПХС ім. проф. М.І. Ситенка НАМН України». На базі цих моделей були створені чотири математичні моделі: 1-а модель — у нормі; 2-а модель — із руйнуванням 50 % об’єму тіла хребця; 3-я модель — із руйнуванням усього тіла хребця та суміжних дисків; 4-а модель — із руйнуванням усього тіла хребця, суміжних дисків, заднього опорного комплексу (дуги та частково суглобів). Побудову геометричних моделей проводили у програмі SolidWorks, кінцево-елементні розрахунки — у програмі ANSYS, статистичну обробку отриманих даних виконували методами Т-тесту для парних вибірок та кореляційного аналізу. Установлено, що в 1-й та 2-й математичних моделях спостерігається достатньо близький збіг результатів з експериментальними моделями — до 30 % в умовах зусиль, не перевищуючих 150 Н, та до 70 % за умови зусилля 200 Н. У разі навантажень понад 200 Н в експериментальних моделях, на відміну від математичних, чітко виражена нелінійна поведінка. У 3-й та 4-й математичних моделях виявлена істотна різниця результатів з експериментом унаслідок нелінійної поведінки експериментальної моделі. Отже, порівняльний аналіз поведінки експериментальної та математичної моделей виявив однакову спрямованість процесів, але без повного збігу отриманих даних. Це означає, що розрахунки на математичній моделі в разі навантаження понад 200 Н можуть показувати неадекватні результати.

Analyze the influence of explosion stress wave on the dynamic fracture of PMMA plates with different curvature radius defects

Defects in brittle solid materials affect the transmission of stress waves, thereby influencing the fracture process of the material. In this paper, the effect of defect curvature radius on the propagation of explosion stress wave and crack propagation is studied. Polymethyl methacrylate (PMMA) is used as the experimental material. The explosive loading and transmission caustics systems are combined to observe and record the explosive fracture process of a PMMA plate with different curvature radius defects. First, the interaction process between the explosion stress wave and defects with different radii of curvature is analyzed via caustics. Then the propagation process of prefabricated defects under the action of the explosion stress wave is studied. Moreover, crack tip propagation speed and the change of the stress intensity factor are simultaneously calculated. Numerical simulation is used to restore the full-field stress change under the action of the explosion stress wave and the defect. Lastly, stress time history curve of the point in the proximity of the defect is analyzed.

Influence of Ultraviolet Radiation on the Morphological and Mechanical Properties of Carbon Fiber-Reinforced Polymers

It is clear that modern carbon fiber (CF) manufacturing methods will go beyond luxurious or limited-use of CF products toward a vast and unlimited commercial evolution of CF uses in multiple engineering applications. This expansion of the unlimited use of CF will be a major challenge for researchers to provide in-depth information to define the mechanical properties of CF products and the extent to which these properties are affected by various environmental factors. Therefore, defining the carbon fiber-reinforced polymer (CFRP) properties under different loading and environmental conditions is critical for extreme operating conditions. Sunlight, heat, and humidity have become a research focus to explore the impact of these parameters on the morphological and mechanical characteristics of the CFRP. This article investigates the influence of sunlight expressed in terms of UltraViolet (UV) light on the morphological and mechanical properties of two different layups of CFRP through tensile testing. The fracture modes were classified based on the ASTM standards to categorize the changes of CFRP with respect to the duration of UV exposure. Furthermore, the observed weight reduction of the exposed CFRP is related to the changes in the mechanical properties. The outcomes show that there is a reduction in tensile strength to approximately 18% for the 45° layup setting and 21% for the 90° layup setting by increasing the UV exposure time to 160 hr. Moreover, the fracture mode was also affected by the UV exposure time, showing more tendency of explosive catastrophic fracture in the center of the specimen at various places, which is known as XMV fracture mode according to ASTM standards.

Mining shovel energy efficiency and its relationship with the explosive fracture of rocks

Production cycles are correlated with the processes of drilling and blasting in rocks. It is shown that energy efficiencies of explosive fracture and shovel operation are interconnected with the face advance velocity. Modeling results on operation per one run of rope power shovels with different bucket capacities are presented. The found approximate relation for the determination of energy efficiency of excavation is based on the interconnection of explosive fracture of rocks, geometry of face and dynamics shoveling.

The structural analysis of the material resulting from the destruction by explosion of a compressed air cylinder

In this paper is presented the structural analysis carried out on samples from a compressed air cylinder subjected to explosion. The air cylinder was mounted on public transport bus. The risk that the incident would repeat with other similar cylinders carrying compressed air required a detailed study regarding the causes that led to the catastrophic degradation. The research by micro and macro structural analysis has highlighted several factors that have increased the damage. The optical micrographs are obtained using an Olympus metallographic microscope equipped with a digital camera, with the possibility to automatically assign the microstructure magnification and with automatic software for linear measurements. The research regarding the appearance of the inner surface of the compressed air cylinder container has highlighted an accentuated corrosion process, developed in the thickness of the cylinder wall with a non-uniform thickness. The break occurred near the welding, known as thermal influence zone (the analyzed cylinder being welded longitudinally). The research has shown that inter-crystalline corrosion associated with pitting (punctiform) corrosion developed between the dendrite branches leads to an intense metal degradation in the wall depth and, in limited cases, causes perforation of the metal wall, increasing the explosive fracture development. A factor that influenced the corrosion process in the ZIT area was the mounting of the compressed air cylinder with the welded area at the bottom of the component.

Numerical Study on the Explosive Separation of Pyrotechnic Cutter

Pyrotechnic cutters are widely used in the wrapping‐band connecting structures of carrier rockets. In this article, a three‐dimensional (3D) finite element model of a pyrotechnic cutter is proposed to determine the influence of the explosive dynamic fracture process and the cutter blade acceleration distance on the cutting effect, using AUTODYN finite element simulation software. Numerical simulations of the cutting process reveal that the initial shear speed, the maximal speed, and the speed at which the cutter connects the rod increase linearly with increasing distance between the cutter blade and the cutting board. As the distance increases, the difference between the initial cutting speed and the maximal speed of the cutter gradually decreases and effectively disappears for a distance of 8.5 mm. At this time, the acceleration effect of the gunpowder gas on the cutter is nearly maximal. When the distance between the cutter and the connecting rod is less than 7.5 mm, the cutting time decreases significantly with increasing spacing. For distances between 7.5 mm and 8.5 mm, the distance has little effect on the cutting time as it increases. There is a small increase in the cutting time, and it can be seen that there is an optimal distance between the cutter and the cutting board during the cutting process. The cutting effect is the strongest for this distance. For the cutter studied in this article, the optimal distance was 7.5 mm. In addition, numerical studies were also performed by varying the maximal cutting diameter of the connecting rod of the pyrotechnic cutter. The discrepancy between the simulation results and actual test data was under 10%, and the simulation result for the cut state of the connecting rod was also consistent with the test result. The simulation results in this article can deepen the understanding of the action mechanism and process of the pyrotechnic cutter and reveal the maximal cutting diameter of the connecting rod of the pyrotechnic cutter under different charging conditions. This provides a reference for future cutter design optimization.

Research trends and design guidelines for fire resistance of structural concrete in South Korea

Research into the fire resistance of structural concrete in South Korea has been ongoing since 2000 and incorporates studies on concrete materials, columns, construction methods and finishing materials. Recently, experiments and analytical studies have been undertaken to include diverse materials and structures for fire resistance. Based on the results of these studies, the South Korean government recognised the need for performance criteria for legal fire-resistant construction and published Regulations for Egress/Fire Protection Construction in 2015. In light of this previous work, this paper provides a review of recent research results for the prevention of the explosive fracture of concrete exposed to high temperatures, analysis of the fire resistance of concrete and recent fire mitigation construction methods. In addition, the paper briefly describes existing specifications for fire resistance design methods in South Korea.

Relaxation phenomena and jointing in ore bodies under explosive injection treatment

Under analysis are relaxation phenomena in ore bodies under leaching. It is shown that liquid and gas–liquid phases make these phenomena last longer, thus it is recommended to apply synergetically interconnected processes of explosive fracture of an ore block and simultaneous injection of active leaching solutions in the generated system of joints.

Fracto-emission in lanthanum-based metallic glass microwires under quasi-static tensile loading

Plastic deformation in metallic glasses is highly localized and often associated with shear banding, which may cause momentary release of heat upon fracture. Here, we report an explosive fracture phenomenon associated with momentary (∼10 ms) light emission (flash) in Lanthanum-based (LaAlNi) metallic glass microwires (dia. ∼50 μm) under quasi-static tensile loading. The load-displacement data as well as the visual information of the tensile deformation process were acquired through an in situ measurement set-up, which clearly showed nonlinear stress (σ)–strain (ϵ) curves prior to yielding and also captured the occurrence of the flash at high fracture stresses (∼1 GPa). Through the postmortem fractographic analysis, it can be revealed that the fracto-emission upon quasi-static loading could be mainly attributed to the localized adiabatic work accumulated at a very large elastic strain confined within the microscale sample volume, followed by a localized high temperature rise up to ∼1000 K at the fracture surface through localized energy dissipation. Our findings suggest that the La-based metallic glass microwires could be useful for energetic microchips, micro-ignition devices, and other functional applications.

Effect of post weld treatment on cracking behaviors of beam-column connections in steel bridge piers

A great number of moment-resisting steel structures collapsed due to ductile crack initiation at welded beam-column connections, followed by explosive brittle fracture in the Kobe (Hyogoken-Nanbu) earthquake in 1995. A series of experimental and numerical studies on cracking behaviors of beam-column connections in steel bridge piers were carried out by the authors

A Study on Low Permeability Formation's Permeability Variation Induced by Explosive Fracturing Technology

The variation of low permeability formation's permeability due to explosive fracturing treatments is studied and a basis to realize and evaluate the effect of the explosive fracturing treatments by contrasting and analyzing the test results of the samples' permeability before and after the explosion experiment is provided. The test result shows that the permeability of those samples increases significantly due to the explosive fracture treatments; the permeability increases as the distance to the explosion center grows at first, then decreases and at last keeps a constant value, which is also much bigger than the initial permeability value.

Directional Fracture Blasting Experimental Study

According to the theories of explosive mechanics and rock fracture dynamics mechanics, carries on the theoretical analysis to the complex slotted seam cartridge, obtains that the complex slotted seam cartridge has the better directional fracture effect. Through the similar simulation experimental study, using the microscopic fracture detection and the macroscopic observation method, a comprehensive analysis of the complex slotted seam cartridge and the conventional slotted seam cartridge's blasting effect, the analysis also indicated that the complex slotted seam cartridge has the better directional fracture effect and the higher energy utilization, and is smaller to the surrounding rock damage.

Experimental Study on Fire Resisting Capacity Using Silicone Compound Material

When fire occurs in a concrete structure, it is hard to extinguish it because of its unique form and location, which results in a very high internal temperature of the maximum 1400°C. Due to the fine structural characteristic of concrete, the structure is likely to suffer fatal damages such as the reduction of resisting force and the damages to the cross section caused by explosive fracture. In this research, the author tested the effect of fire on structures by using fire boards with perlite-added silicone and confirmed that the fire resisting capacity varies according to the weight ratio of the addition agent, which shows what effect perlite has for the pyrolysis process. A fire resisting capacity test was also carried out by attaching a silicone composite fire board to a real size specimen. As a result of the test carried out by installing the fire boards with different thickness by section, most fire boards had excellent fire resisting capacity, and fire boards with 20mm or more thickness had also excellent fire resisting capacity

방화석고보드 부착이 섬유혼입 고강도 콘크리트 모의 기둥부재의 내화특성 및 잔존내력에 미치는 영향

본 연구는 50 MPa급 고강도 콘크리트 모의 기둥부재를 대상으로 PF섬유 혼입 및 방화석고보드를 부착하므로써, 내화특성 및 잔존내력에 대하여 검토하였다. 먼저, 모체 콘크리트의 기본 물성은 모두 목표 범위를 만족하는 것으로 나타났다. 내부 온도이력은 방화석고보드가 미부착된 경우 온도가 다소 높게 나타나는 경향을 보였고, 방화석고보드가 부착된 경우는 섬유 혼입율이 증가할수록 온도가 점차 낮게 분포되었다. 상호관계로는 시간이 경과할수록 섬유가 혼입된 경우에서 낮은 온도분포를 나타내었으며, 보드가 부착되었을 때 더욱 낮은 온도 경향을 확인할 수 있었다. 한편, 외관성상은 PF 0 %에서 심한 파괴 폭렬 현상이 발생하였으며, 섬유혼입율이 증가할수록 탈락 현상은 방지되었으나, 색상 변질 및 다수의 균열이 발견되었고, 보드가 부착된 경우는 혼입율이 증가할수록 외관이 양호해지는 경향을 나타내었다. 잔존 압축강도로 보드 미부착 PF 0 %에서는 강도측정이 불가능하였으며, 섬유혼입율이 증가할수록 강도는 증가하였으나, 약 30~40 %의 강도저하 현상을 나타내었고, 보드 부착 PF 0 %의 경우 강도측정은 가능하였으나 약 80 % 가량 강도가 저하하였으며, 섬유혼입율이 증가할수록 저하폭은 감소하여 약 10~20 %의 강도 저하만을 나타내었다. 이상을 종합하면, PF섬유 혼입 및 방화석고보드 부착을 개별적으로 사용하는 것보다는 두 가지 방법을 복합적으로 적용할 때 내화성능 향상에 있어서 보다 효과적일 것으로 분석되었다. In this study, fire resistance and residual strength were examined after the addition of PF fiber and bonding fireproofing gypsum board to a high strength concrete-model column of 50 MPa grade. At the beginning of the experiment, all the properties of base concrete appeared to satisfy the target range. In terms of the internal temperature record, a trend of slightly high temperature was shown when the fireproofing gypsum board was not bonding, and when the fireproofing gypsum board was bonding, as PF content increased gradually, the temperature was gradually lowered. In terms of the relationship, as time elapsed a low temperature was shown when fiber was mixed, and when the board was bonding, the trend of lower temperature could be confirmed. Meanwhile, in terms of spalling property, a severe explosive fracture was generated at PF 0%, and falling off was prevented as the fiber content was increased; however, discoloration and a multitude of cracks were discovered, and when the board was bonding, the trend in which the exterior became satisfactory when the content was increased emerged. In terms of the residual compressive strength, measuring of strength could not be performed at PF 0% without bonding of board, and the strength was increased as the fiber content was increased; however, there was a decrease in strength of about 30 ~ 40%, and in the case of PF 0% with the bonding of board, the strength could be measured; however, about an 80% decrease in strength was shown, and only about a 10 ~ 20% decline in strength was displayed, as the range of decrease was reduced as the fiber content was increased. Considering all of these factors, it was determined that a more efficient enhancement of fire resistance was obtained when two methods are applied in combination rather than when the PF fiber content and bonding of fireproofing gypsum board are utilized individually.