Influence Of Crack Propagation Research Articles

Iron ore grade's impact on uniaxial compression behavior and acoustic emission characteristics

The mechanical properties of iron ore are influenced by various factors, including its grade, which consequently impacts stope stability and equipment efficiency in the mining process. In order to explore the influence and mechanism of grade on these properties, handheld XRF testing was conducted to determine the grade of iron ore samples ranging from 28% to 40%. Subsequently, the acoustic emission method was employed to acquire signals during the uniaxial compression tests. Additionally, scanning electron microscopy was utilized to examine the fracture surface, for performing a microscopic analysis of the influence mechanism of grade on the mechanical properties of iron ore. The results revealed that lower-grade iron ore exhibited larger transverse deformation, with a corresponding dominance of tensile failure. This observation aligned with the AF-RA value (Parameters of reaction crack type), which depicted a shift in the types of microcracks generated during the compression process from tensile cracks to shear cracks with the increasing grade. The content of gangue minerals diminishing as the grade increased. Consequently, the location of the cracks transitioned from the primary failure Through the gangue minerals to the primary microcracks in metallic minerals, resulting in a higher occurrence of acoustic emission events during the early loading stage and the development speed of microcracks accelerates during the loading process. The dominant frequency (Parameters of reaction crack size) of the acoustic emission signal increased from 150 kHz at a grade of 28% to 264 kHz at a grade of 40%, accompanied by a linear decrease in the proportion of low-frequency signals. The b value (indicator for quantifying the degree of damage) demonstrates a decrease with increasing grade. Overall, the content of metal minerals in the iron ore increased with the grade, resulting in polymerization. However, the influence of crack propagation on the overall strength of iron ore remained relatively minor. Macroscopically, the uniaxial compressive strength increased almost linearly with the iron ore grade.

Influence of crack propagation on the seismic behavior of historic rammed earth buildings: The Tower of Muhammad in the Alhambra (Spain)

The presence of defects in the form of cracks is frequent in rammed earth historic buildings located in seismic zones. The influence of these cracks, however, has not been directly taken into account in the numerical models for this kind of structures existing to date in the literature. In this light, this study presents an analysis of a FEM model of a heritage rammed earth structure – Tower of Muhammad of the Alhambra – under gravity loads and a seismic action, with and without the existing cracks, with the aim of assessing their influence. The results show that the inclusion of cracks in the model significantly influence the structural behavior of the building, changing the stress distribution and reducing its stiffness and load capacity. The model with cracks is also able to accurately show damage location in the walls due to crack propagation.

Predicting the electromechanical properties of small caliber projectile impact igniter using PZT dynamic damage constitutive model considering crack propagation

Block piezoelectric ceramics (PZTs) are often used in impact igniters to provide activation energy for electric initiators. Under the action of strong impact stress, PZTs release electric energy accompanied by crack initiation, propagation and crushing. At present, the electrical output performance of PZTs in projectile is usually calculated by quasi-static piezoelectric equation without considering the dynamic effect caused by strong impact and the influence of crack propagation on material properties. So the ignition parameters are always not accurately predicted. To tackle this, a PZT dynamic damage constitutive model considering crack propagation is established based on the dynamic impact test and the crack propagation theory of brittle materials. The model is then embedded into the ABAQUS subroutine and used to simulate the electromechanical response of the impact igniter during the impact of a small caliber projectile on the target. Meanwhile, the experiments of projectile with impact igniter impact on the target are carried out. The comparison between experimental and numerical simulation results show that the established dynamic damage model can effectively predict the dynamic electromechanical response of PZTs in the missile service environment.

Research on damage progression of drill string material based on the extended finite element method.

In this paper, the process of crack propagation is investigated using the extended finite element method at the mesoscale to study the drill pipe fracture mechanism. Firstly, the property of the S135 drill pipe was analyzed through physical and chemical experiments and the scanning electron microscope method. After that, a grain distribution model of the drill pipe material at the mesoscale was established by the Python scripting language on ABAQUS platform. Furthermore, the extended finite element method was applied to study crack dynamic propagation. And the distribution of stress and strain during the crack propagation were obtained at the mesoscale grain model. Finally, by the mesomechanics "homogenization" method, the stress and strain of the crack propagation model at different times were analyzed, and the influence of crack propagation on drill pipe material was obtained. Simulation results show that, although drill pipe material at the macroscopic scale is in the elastic stage, plastic zone and micro-crack propagation may also exist at the mesoscale. The proposed method in this paper studied the stress distribution in the crack tip during the propagation, which is a benefit for exploring the fracture mechanism of drill pipe.

Indentation size effect–crack propagation model and finite element simulation verification for microhardness test of ceramic materials

In this study, an indentation size effect–crack propagation model for hard and brittle materials in microhardness testing was proposed on the basis of the relationship between the size effects in microhardness testing and the generation and propagation of cracks in an indentation area. Results showed that crack length and crack opening angle were the main factors that influenced the size effect. The longer the crack length, the larger the crack opening angle, and the more obvious the size effect. The generation and propagation of cracks in the indentation region of ultrafine-grained Si2N2O–Si3N4 ceramics during microhardness testing were simulated on ABAQUS finite element software. The distributions of displacement field, strain field, and stress field in the indentation area with the presence of cracks was analyzed, the influence of crack propagation on the elastic recovery of the indentation area was discussed, and the correctness of the size effect–crack propagation model was verified.

Factors affecting the fatigue strength of thin-plates in large structures

This paper studies the main factors affecting the fatigue strength assessment of thin plates in large structures. The first part of study includes the influence of initial distortions, joints’ flexibility and surrounding structure on structural stress analysis of welded joint. The second part covers the influence of joint and its geometrical properties on fatigue strength modelling. The third part includes also the material elastic-plastic behaviour and the influence of crack propagation. The results show that if the structural analysis considers secondary bending properly, the local elastic fatigue damage parameters such as J-integral range can be used to model fatigue strength at 2–5million load cycles. However, to explain the slope variation of the fatigue resistance curve, the consideration of material elastic-plastic behaviour and short crack growth is needed. The strain-based crack growth simulations indicate that longer short crack growth period is the reason for the higher slope value. The importance of short crack growth is dependent on the weld notch geometry and plate thickness.

Fault Diagnosis for a Multistage Planetary Gear Set Using Model-Based Simulation and Experimental Investigation

The gear damage will induce modulation effects in vibration signals. A thorough analysis of modulation sidebands spectral structure is necessary for fault diagnosis of planetary gear set. However, the spectral characteristics are complicated in practice, especially for a multistage planetary gear set which contains close frequency components. In this study, a coupled lateral and torsional dynamic model is established to predict the modulation sidebands of a two-stage compound planetary gear set. An improved potential energy method is used to calculate the time-varying mesh stiffness of each gear pair, and the influence of crack propagation on the mesh stiffness is analyzed. The simulated signals of the gear set are obtained by using Runge-Kutta numerical analysis method. Meanwhile, the sidebands characteristics are summarized to exhibit the modulation effects caused by sun gear damage. At the end, the experimental signals collected from an industrial SD16 planetary gearbox are analyzed to verify the theoretical derivations. The results of experiment agree well with the simulated analysis.

Influence of crack propagation on electrical resistivity and ultrasonic characteristics of normal concrete assessed by sequential TPB fracture test

The paper is focused on the investigation of the effect of tensile failure propagation on the change in values of electrical resistivity and ultrasound pulse passing time within the central section of beam bend specimens made of normal concrete. These two physical characteristics may be employed as a quality indicator of the concrete cover within the procedures of the assessment of the structural durability. The three-point bending test configuration was utilised to drive the crack propagation process through several loading–unloading cycles, between which, the electrical resistivity and ultrasonic measurements over the fractured region were performed. Equivalent elastic crack model was used for estimation of the fracture progression (described via the effective crack length increment) at those loading stages. The relationships between changes of the non-destructively determined parameters, the effective crack length and the distance from crack tip are discussed with respect to two variants of treatment of the test specimens’ surface: the pre-dried surface and the wet surface. A difference between the ultrasonic and electrical resistivity measurements ability with respect to crack width is found in the case of wet samples.

Failure Simulation of Single-Edge Notched Concrete Beam under Dynamic Tensile Loading

Crack growth of concrete beam under dynamic tensile loading is a typical discontinuous problem. It is difficult to realize the process of crack propagation using the conventional finite element method, but the extended finite element method (XFEM) is an effective method to analyze the fracture developed in recent years. This paper introduces the basic principle of XFEM and the analysis method of simulating concrete cracking and crack propagation with XFEM. At the end the crack expansion process of the concrete specimen with initial crack and dynamic load is done. The influence of crack propagation on concrete beam stresses and displacements and the crack propagation laws under dynamic tension is studied. The case shows the unique advantage of XFEM in the crack propagation analysis field.

Stress-strain characteristic of SFRC using recycled fibres

This paper presents work from a comprehensive study on the development of a flexural design framework for concrete reinforced with steel fibres that are recovered from used tyres. The experimental flexural behaviour of notched concrete prisms reinforced with these fibres is initially presented. For comparison purposes, prisms reinforced with industrially produced fibres are also considered. An attempt to adopt an existing RILEM design framework to derive appropriate tensile stress-strain blocks is made, but problems are identified with key parameters of the framework. The influence of crack propagation and location of neutral axis depth on the tensile stress distribution is examined. Following an analytical study, it is concluded that the uniaxial stress-strain model, proposed by RILEM overestimates the load-carrying capacity and should be modified by utilising more advanced analytical techniques.