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Effect of fly ash replacement level on the fracture behavior of concrete

Mahdi AREZOUMANDI, Jeffery S. VOLZ

《结构与土木工程前沿（英文）》 2013年第7卷第4期页码 411-418 doi: 10.1007/s11709-013-0228-4

摘要： The production of portland cement–the key ingredient in concrete–generates a significant amount of carbon dioxide. However, due to its incredible versatility, availability, and relatively low cost, concrete is the most consumed manmade material on the planet. One method of reducing concrete’s contribution to greenhouse gas emissions is the use of fly ash to replace a significant amount of the cement. ?This study presents the results of an experimental investigation that evaluates effect of fly ash replacement level on the fracture energy of concrete. This study includes four mixes with 0%, 30%, 50%, and 70% fly ash as a cement replacement. This experimental program consisted of 32 fracture beams to study the fracture behavior of concrete. The experimental fracture energies were compared with the fracture energy provisions of different design codes and also different analytical equations. Furthermore, statistical data analyses (parametric and non-parametric) were performed to evaluate whether or not there is any statistically significant difference between the experimental fracture energies of different mixes. Results of these statistical tests show that the mix with higher level of fly ash replacement level has higher fracture energy.

关键词： concrete fracture energy fly ash

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聚能效应在岩石定向断裂控制爆破中的研究

罗勇,沈兆武

《中国工程科学》 2006年第8卷第6期页码 78-82

摘要：

针对目前石材开采面临的问题，对采用聚能药包岩石定向断裂控制爆破技术时的裂缝（纹）起裂和扩展的机理进行了探讨，同时对该法的爆破参数进行了设计；实验室和现场试验验证结果表明，由聚能射流形成的切缝有明显的定向作用，使爆生气体的能量沿预定方向集中，裂纹的定向断裂控制效果良好，表明该法是一种比较理想的断裂控制爆破技术；研究成果对相关理论研究和现场应用均有一定的指导意义，该法将会成为岩石定向断裂控制爆破发展的一个方向。

关键词：聚能效应定向断裂爆破模型试验药型罩致裂

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Experimental investigations of internal energy dissipation during fracture of fiber-reinforced ultra-high-performance

Eric N. LANDIS, Roman KRAVCHUK, Dmitry LOSHKOV

《结构与土木工程前沿（英文）》 2019年第13卷第1期页码 190-200 doi: 10.1007/s11709-018-0487-1

摘要： Split-cylinder fracture of fiber-reinforced ultra-high-performance concrete (UHPC) was examined using two complementary techniques: X-ray computed tomography (CT) and acoustic emission (AE). Fifty-mm-diameter specimens of two different fiber types were scanned both before and after load testing. From the CT images, fiber orientation was evaluated to establish optimum and pessimum specimen orientations, at which fibers would have maximum and minimum effect, respectively. As expected, fiber orientation affected both the peak load and the toughness of the specimen, with the optimum toughness being between 20% and 30% higher than the pessimum. Cumulative AE energy was also affected commensurately. Posttest CT scans of the specimens were used to measure internal damage. Damage was quantified in terms of internal energy dissipation due to both matrix cracking and fiber pullout by using calibration measurements for each. The results showed that fiber pullout was the dominant energy dissipation mechanism; however, the sum of the internal energy dissipation measured amounted to only 60% of the total energy dissipated by the specimens as measured by the net work of load. It is postulated that localized compaction of the UHPC matrix as well as internal friction between fractured fragments makes up the balance of internal energy dissipation.

关键词： ultra-high-performance concrete concrete fracture X-ray computed tomography acoustic emission

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A new fracture criterion for peridynamic and dual-horizon peridynamics

Jinhai ZHAO, Hesheng TANG, Songtao XUE

《结构与土木工程前沿（英文）》 2018年第12卷第4期页码 629-641 doi: 10.1007/s11709-017-0447-1

摘要： A new fracture criterion based on the crack opening displacement for peridynamic (PD) and dual-horizon peridynamics (DH-PD) is proposed. When the relative deformation of the PD bond between the particles reaches the critical crack tip opening displacement of the fracture mechanics, we assume that the bond force vanishes. A new damage rule similar to the local damage rule in conventional PD is introduced to simulate fracture. The new formulation is developed for a linear elastic solid though the extension to nonlinear materials is straightforward. The performance of the new fracture criterion is demonstrated by four examples, i.e. a bilateral crack problem, double parallel crack, monoclinic crack and the double inclined crack. The results are compared to experimental data and the results obtained by other computational methods.

关键词： Castigliano’s theorem breaking energy critical extension XFEM COD PD-COD

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Early-life famine exposure, adulthood obesity patterns, and risk of low-energy fracture

《医学前沿（英文）》 doi: 10.1007/s11684-023-1023-9

摘要： Malnutrition in early life increases the risk of osteoporosis, but the association of early-life undernutrition combined with adulthood obesity patterns with low-energy fracture remains unknown. This study included 5323 community-dwelling subjects aged ≥40 years from China. Early-life famine exposure was identified based on the participants’ birth dates. General obesity was assessed using the body mass index (BMI), and abdominal obesity was evaluated with the waist-to-hip ratio (WHR). Low-energy fracture was defined as fracture occurring after the age of 40 typically caused by falls from standing height or lower. Compared to the nonexposed group, the group with fetal, childhood, and adolescence famine exposure was associated with an increased risk of fracture in women with odds ratios (ORs) and 95% confidence intervals (CIs) of 3.55 (1.57–8.05), 3.90 (1.57–9.71), and 3.53 (1.05–11.88), respectively, but not in men. Significant interactions were observed between fetal famine exposure and general obesity with fracture among women (P for interaction = 0.0008). Furthermore, compared with the groups with normal BMI and WHR, the group of women who underwent fetal famine exposure and had both general and abdominal obesity had the highest risk of fracture (OR, 95% CI: 3.32, 1.17–9.40). These results indicate that early-life famine exposure interacts with adulthood general obesity and significantly increases the risk of low-energy fracture later in life in women.

关键词： famine obesity body mass index waist-to-hip ratio low-energy fracture

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Tests on impact effect of partial fracture at steel frame connections

CHEN Yiyi, BIAN Ruoning

《结构与土木工程前沿（英文）》 2008年第2卷第4期页码 295-301 doi: 10.1007/s11709-008-0049-z

摘要： Impact effect of sudden fracture at steel frame connections under severe earthquake or other extreme loads is presented in this paper. The relation of impulse caused by structural fracture to the release of inner force at the cracked location, the magnitude of the response to impact on the basis of one degree of freedom model, and the ratio of the peak value of response to natural period of the system are investigated. Two types of fracture tests were designed and carried out both on uniaxial steel bar tensioned and moment resistant steel frame model. It is proven that the response during the fracture process can be measured quite well using high-frequency data processing system. It is also revealed that the instant fracture of structural connection is characterized by progressive and partial fracture. Numerical evaluation of the impact effect of connection fracture is carried out.

关键词： structural fracture natural fracture progressive high-frequency

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Computational modeling of fracture in concrete: A review

Luthﬁ Muhammad Mauludin, Chahmi Oucif

《结构与土木工程前沿（英文）》 2020年第14卷第3期页码 586-598 doi: 10.1007/s11709-020-0573-z

摘要： This paper presents a review of fracture modeling of concrete. The complex material, such as concrete, has been widely used in construction industries and become trending issue in the last decades. Based on comprehensive literature review, there are two main approaches considered to-date of concrete fracture modeling, such as macroscopic and micromechanical models. The purpose of this review is to provide insight comparison from different techniques in modeling of fracture in concrete which are available. In the first section, an overview of fracture modeling in general is highlighted. Two different approaches both of macroscopic and micromechanical models will be reviewed. As heterogeneity of concrete material is major concern in micromechanical-based concrete modeling, one section will discuss this approach. Finally, the summary from all of reviewed techniques will be pointed out before the future perspective is given.

关键词： concrete fracture macroscopic micromechanical heterogeneity

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Computational modeling of fracture in capsule-based self-healing concrete: A 3D study

《结构与土木工程前沿（英文）》 2021年第15卷第6期页码 1337-1346 doi: 10.1007/s11709-021-0781-1

摘要： We present a three-dimensional (3D) numerical model to investigate complex fracture behavior using cohesive elements. An efficient packing algorithm is employed to create the mesoscale model of heterogeneous capsule-based self-healing concrete. Spherical aggregates are used and directly generated from specified size distributions with different volume fractions. Spherical capsules are also used and created based on a particular diameter, and wall thickness. Bilinear traction-separation laws of cohesive elements along the boundaries of the mortar matrix, aggregates, capsules, and their interfaces are pre-inserted to simulate crack initiation and propagation. These pre-inserted cohesive elements are also applied into the initial meshes of solid elements to account for fracture in the mortar matrix. Different realizations are carried out and statistically analyzed. The proposed model provides an effective tool for predicting the complex fracture response of capsule-based self-healing concrete at the meso-scale.

关键词： 3D fracture self-healing concrete spherical cohesive elements heterogeneous

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Evaluating the material strength from fracture angle under uniaxial loading

Jitang FAN

《结构与土木工程前沿（英文）》 2019年第13卷第2期页码 288-293 doi: 10.1007/s11709-018-0480-8

摘要： The most common experimental methods of measuring material strength are the uniaxial compressive and tensile tests. Generally, shearing fracture model occurs in both the tests. Compressive strength is higher than tensile strength for a material. Shearing fracture angle is smaller than 45° under uniaxial compression and greater than 45° under uniaxial tension. In this work, a unified relation of material strength under uniaxial compression and tension is developed by correlating the shearing fracture angle in theory. This constitutive relation is quantitatively illustrated by a function for analyzing the material strength from shear fracture angle. A computational simulation is conducted to validate this theoretical function. It is full of interest to give a scientific illustration for designing the high-strength materials and engineering structures.

关键词： strength fracture mechanics

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A dimensional analysis on asphalt binder fracture and fatigue cracking

Qian ZHAO, Zhoujing YE

《结构与土木工程前沿（英文）》 2018年第12卷第2期页码 201-206 doi: 10.1007/s11709-017-0402-1

摘要： Fracture and fatigue cracking in asphalt binder are two of most serious problems for pavement engineers. In this paper, we present a new comprehensive approach, which consists both of dimensional analysis using Buckingham Theorem and -integral analysis based on classic fracture mechanics, to evaluate the fracture and fatigue on asphalt binder. It is discovered that the dimensional analysis could provide a new perspective to analyze the asphalt fracture and fatigue cracking mechanism.

关键词： Dimensional analysis asphalt fracture fatigue cracking

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Experimental research on ductile fracture criterion in metal forming

Song YU, Weiming FENG

《机械工程前沿（英文）》 2011年第6卷第3期页码 308-311 doi: 10.1007/s11465-011-0233-z

摘要：

Ductile fracture criterion is key limitation parameter in material forming. Accuracy predicting surface and internal failure in plastic deformation process affects on the technology design of workpiece and die greatly. Tension, compression, torsion and shearing test on 45# steel are utilized for providing the experimental values of the critical values at fracture, and 11 widely used ductile fracture criterion are selected to simulate the physical experiments and their relative accuracy for predicting and quantifying fracture initiation sites are investigated. The comparing results show that metal forming process under high triaxiality can be estimated successively using both Normalized Cockcroft-latham and the Brozzo ductile fracture criteria, but the Ayada and general Rice-Tracey model work very well for the low triaxiality cases.

关键词： ductile fracture criteria metal forming process material experiment stress triaxiality

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Fracture behavior of two non-symmetrical collinear cracks emanating from an elliptical hole in a piezoelectric

Junhong GUO, Zixing LU

《机械工程前沿（英文）》 2011年第6卷第3期页码 296-300 doi: 10.1007/s11465-011-0236-9

摘要：

Based on the Stroh-type formalism and the technique of conformal mapping, the problem of two non-symmetrical collinear cracks emanating from an elliptical hole in a piezoelectric solid is investigated under remotely uniform in-plane electric loading and anti-plane mechanical loading, which allowed us to take the electric field inside the hole and cracks into account. The analytical solutions of the field intensity factors and the energy release rate are presented in closed-form, which includes the extreme cases for an impermeable crack and a permeable crack. Numerical results are then presented to reveal the effects of geometrical parameters, crack permeability and combined mechanical and electric loadings on the energy release rate.

关键词： piezoelectric materials elliptical hole semi-permeable crack energy release rate analytic solution

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Hybrid deep learning model for risk prediction of fracture in patients with diabetes and osteoporosis

《医学前沿（英文）》 2022年第16卷第3期页码 496-506 doi: 10.1007/s11684-021-0828-7

摘要： The fracture risk of patients with diabetes is higher than those of patients without diabetes due to hyperglycemia, usage of diabetes drugs, changes in insulin levels, and excretion, and this risk begins as early as adolescence. Many factors including demographic data (such as age, height, weight, and gender), medical history (such as smoking, drinking, and menopause), and examination (such as bone mineral density, blood routine, and urine routine) may be related to bone metabolism in patients with diabetes. However, most of the existing methods are qualitative assessments and do not consider the interactions of the physiological factors of humans. In addition, the fracture risk of patients with diabetes and osteoporosis has not been further studied previously. In this paper, a hybrid model combining XGBoost with deep neural network is used to predict the fracture risk of patients with diabetes and osteoporosis, and investigate the effect of patients’ physiological factors on fracture risk. A total of 147 raw input features are considered in our model. The presented model is compared with several benchmarks based on various metrics to prove its effectiveness. Moreover, the top 18 influencing factors of fracture risks of patients with diabetes are determined.

关键词： XGBoost deep neural network healthcare risk prediction

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A concise review about fracture assessments of brittle solids with V-notches

Hsien-Yang YEH, Bin YANG

《结构与土木工程前沿（英文）》 2019年第13卷第2期页码 478-485 doi: 10.1007/s11709-019-0520-z

摘要：

A concise review of recent studies about the fracture assessments of elastic brittle solid materials containing V-notches is presented. In this preliminary and brief survey, elastic stress distributions in V-notched solids are discussed first. The concept of notch stress intensity factor is introduced. Combine the digital image correlation method with numerical computation techniques to analyze the stress distribution near the notches. Fracture criteria such as strain energy density, J-integral, theory of critical distance are used.

关键词： fracture assessment brittle solids V-notches review

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Mechanical properties and impact resistance of concrete composites with hybrid steel fibers

Fatih ÖZALP; Halit Dilşad YILMAZ; Burcu AKCAY

《结构与土木工程前沿（英文）》 2022年第16卷第5期页码 615-623 doi: 10.1007/s11709-022-0828-y

摘要： The aim of this study is to develop concrete composites that are resistant to armor-piercing projectiles for defense structures. Different reinforcement configurations have been tested, such as short steel fibers, long steel fibers, and steel mesh reinforcement. Three different concrete mix designs were prepared as “Ultra High Performance (UHPFRC), High Performance (HPFRC) and Conventional (CFRC) Fiber Reinforced Concrete”. The content of hybrid steel fibers was approximately 5% in the UHPFRC and HPFRC mixtures, while the steel fiber content was approximately 2.5% in the CFRC mixture. In addition, a plain state of each mixture was produced. Mechanical properties of concrete were determined in experimental studies. In addition to the fracture energy and impact strength, two important indicators of ballistic performance of concrete are examined, which are the penetration depth and damage area. The results of the study show that the depth of penetration in UHPFRC was around 35% less than that in HPFRC. It was determined that the mixtures of UHPFRC and HPFRC containing 5% by volume of hybrid steel fibers showed superior performance (smaller crater diameter and the less projectile penetration depth) against armor-piercing projectiles in ballistic tests and could be used in defense structures.

关键词： projectile impact depth of penetration fracture energy crater diameter UHPFRC