卵形弹侵彻混凝土靶的耦合侵蚀模型

弹体在高速侵彻混凝土介质过程中会出现明显的侵蚀现象,导致弹体发生质量损失和弹头钝化。据已有的实验观察,弹体表面熔化和骨料切削是侵蚀发生的主要机制。该文基于动态空腔膨胀理论并结合弹体表面熔化和骨料切削这两种机制,提出一种耦合两种机制的耦合质量侵蚀模型。该模型通过二维热传导和改进的Rabinowizc磨损理论分别获取弹体表面熔化和骨料对弹体切削而造成的弹体质量损失,通过Johnson-Cook本构将温度和切削两种机制联系起来,进而建立了结合熔化机制和切削机制的耦合质量侵蚀模型。将耦合模型预测的弹体侵彻深度和质量损失率等参数并与实验结果进行对比,对比结果表明模型的理论预测与实验数据有较好的吻合度,验证了该文耦合模型结合熔化和切削机制的合理性。最后,讨论了侵彻过程中弹体的相关运动参数演变过程,为弹体侵彻中侵蚀现象问题的研究提供一定参考。     

Depth of penetration of high-speed penetrator with including the effect of mass abrasion

Mass abrasion is observed on the nose of projectile when a projectile strikes concrete target at high velocity. To evaluate the influence of the mass abrasion on the depth of penetration (DOP) limit, the relationship between the nose factor of the residual projectile after abrasion and the initial impact velocity is suggested according to the experimental data. Based on the dynamic cavity expansion theory, with considering the effects of varying nose factor and mass of projectile, a modified model is proposed to calculate the depth of penetration of kinetic energy penetrator. The model predicts that a theoretical maximum DOP exists due to the mass abrasion of the projectile. The model is checked by the different experimental data.     

An investigation on mass loss of ogival projectiles penetrating concrete targets

Mass loss of an ogival projectile during its normal penetration in concrete target was investigated in this paper. Experiments of 38CrSi short-rod projectiles with ogival nose shape penetrating into concrete targets were conducted in the striking velocity range of 500–1500 m/s. Discussions revealed that projectile mass loss derives mainly from the nose part for both short-rod and long-rod projectiles during the penetration process. Furthermore, an engineering model was proposed to determine upper limit of rigid penetration regime as the maximum value of the striking velocity, which was based on the feature of projectile mass loss in the hydrodynamic transition between rigid penetration regime and semi-hydrodynamic penetration regime. Good agreements are obtained between engineering predictions and experimental results.     

20SiMn低合金钢和0Cr13Ni5Mo不锈钢的多相流损伤行为

对水轮机用金属材料20SiMn低合金钢和0Cr13Ni15Mo不锈钢进行旋转圆盘仪空蚀和冲刷磨损单元和组合多相流损伤实验。结果表明，20SiMn低合金钢和0Cr13Ni15Mo不锈钢的冲刷磨损及空蚀和冲刷磨损联合作用损伤累积质量损失－时间曲线均呈线性关系，空蚀和冲刷磨损联合作用对材料造成的损伤显著高于空蚀和冲刷磨损单独作用，空蚀和冲刷磨损的交互作用在空蚀和冲刷磨损联合作中起重要的作用；在空蚀和冲刷损联合作用中，液体空化及随后的空泡溃灭改变了流体中固相颗粒的运动方向，引起固相颗粒的流速增加和攻角改变，从而加剧了固相颗粒对材料表面的损伤。     

Scaling numerical models for hypervelocity test sled slipper-rail impacts

Hypervelocity test sled slipper-rail impacts have been simulated numerically using the finite volume hydrocode, ChartD to the Three-Halves (CTH). This study addresses the difficulties of applying CTH model solutions to real test sled runs. Past CTH models using dimensions different than actual test sleds have been used to study phenomenological aspects of the problem. However, quantitative results from the CTH model solution do not apply directly to actual test sled runs due to strain rate effects and time scale differences. The Buckingham Pi Theorem is applied to two potential hypervelocity gouging models. Validity of the invariant products is tested using sample CTH hypervelocity gouging models that are scaled up to simulate dimensions of a real test sled. Real test sled dimensions are desired in order to more closely simulate actual test sled runs. Invariant products developed from application of the Buckingham Pi Theorem can be used as guidelines for determining whether a CTH model is applicable to a test sled with specific dimensions. Strain rate effects are investigated to study whether deviations between scaled CTH models may be reduced by modifying the constitutive model.     

A model for prediction of time from corrosion initiation to corrosion cracking

Prediction of time to corrosion cracking is a key element in evaluating the service life of corroded reinforced concrete (RC) structures. This paper presents a mathematical model that predicts the time from corrosion initiation to corrosion cracking. In the present model a relationship between the steel mass loss and the internal radial pressure caused by the expansion of corrosion products is developed. The concrete around a corroding steel reinforcing bar is modeled as a thick-walled cylinder with a wall thickness equal to the thinnest concrete cover. The concrete ring is assumed to crack when the tensile stresses in the circumferential direction at every part of the ring have reached the tensile strength of concrete. The internal radial pressure at cracking is then determined and related to the steel mass loss. Faraday’s law is then utilized to predict the time from corrosion initiation to corrosion cracking. The model accounts for the time required for corrosion products to fill a porous zone before they start inducing expansive pressure on the concrete surrounding the steel reinforcing bar. The accuracy of the model is demonstrated by comparing the model’s predictions with experimental data published in the literature.     

Relation between abrasion resistance and flexural strength of high volume fly ash concrete

In this paper, abrasion of high volume fly ash (HVFA) concretes made with 50% and 70% of cement replacement with fly ash was assessed in terms of its relation to flexural tensile strength. Comparisons were made between normal Portland cement (NPC) concrete and fly ash concrete. Comparisons were also made between fly ash concretes. Investigation results have shown that the abrasion resistance increased as flexural tensile strength increased. Analysis of the results showed that, for concrete with tensile strength of greater than 4–5 MPa, the abrasion resistance of HVFA concrete with 70% replacement with cement was found to be higher than that of counterpart control NPC concrete and concrete made with 50% fly ash. The comparison between the relation of abrasion to compressive strength and abrasion to flexural tensile strength made in terms of R² of the linear regression showed that a stronger relation existed between abrasion and flexural tensile strength than that of abrasion to compressive strength of the concrete studied.

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Résumé L'étude a pour but d'estimer la relation entre la résistance à l'usure avec la résistance à la traction en flexion des bétons contenant de 50% et 70% de cendres volantes. On a comparé le béton pur au béton contenant des cendres volantes. Des comparaisons ont été faites également entre les différents bétons contenant des cendres volantes. Les resultats de la recherche ont montré que la résistance à l'usure augmente à mesure que la résistance à la traction en flexion de 4∼5 MPa ont une résistance à l'usure plus grande s'ils contienneint 70% de cendres volantes que s'ils étaient purs ou contenaient 50% de cendres volantes. La comparaison entre les relation de la résistance à l'usure en compression et de la résistance à l'usure en traction a été établie en termes de R² de la régression linéaire. On a prouvé qu'une relation plus forte a été obtenue entre la résistance à l'usure et la résistance à la traction en flexion par rapport à la résistance à l'usure en compression du béton étudié.

     

Field investigations of abrasion resistance

An extensive field investigation has been undertaken to assess the abrasion resistance of concrete floors in industrial premises. The performance was expressed in terms of the depth of wear produced by an accelerated abrasion machine, which simulated the damage mechanisms in a typical warehouse or factory. The results were used to compare site and laboratory practices, and this demonstrated that results obtained solely with laboratory methods may not be applicable to industrial concrete floor slabs. A comparison between the results obtained from the accelerated abrasion test and subjective assessments of service wear, showed a general agreement, and indicated that the apparatus provides a means for assessing the quality of concrete floor slabs in terms of abrasion resistance.     

Application of factorial models to predict the effect of anti-washout admixture, superplasticizer and cement on slump, flow time and washout resistance of underwater concrete

The anti-washout underwater concrete posses different properties from conventional underwater concrete. When an anti-washout admixture is mixed with concrete, the viscosity of the concrete is increased and its resistance to washout is enhanced. Superplasticizer ensures enough concrete fluidity to spread readily in place without vibration. A factorial design was carried out to mathematically model the influence of three key parameters on slump, flow time measured by Orimet and mass loss by washout of underwater concrete. The parameters considered in this investigation were the dosage of cement, the concentrations of anti-washout admixture and superplasticizer. All mixes were made with 0.43 water/cement ratio which correspond a typical underwater concrete. The proposed models are valid for concretes with cement dosage ranging between 420 kg/m³ to 520 kg/m³ and the concentrations of anti-washout admixture and superplasticizer varying between 0.02%–0.13% and 0.4%–1.8%, by mass of cement, respectively. Test results of the models indicated that the slump is highly affected, in order of importance, by dosage of cement and the dosage of superplasticizer, then by the concentration of anti-washout admixture. The mass loss by washout is influenced, in order of significance, by the concentration of anti-washout admixture, the dosage of cement, the concentration of superplasticizer and the interaction between the dosages of cement and anti-washout admixture. The flow time is affected, in order of importance, by the dosage of cement, the concentration of superplasticizer and the interaction between these parameters. This model can be used as a tool to facilitate the test protocol required to optimise the underwater concrete.     

Microscopic, physical and mechanical analysis of polypropylene fiber reinforced concrete

This investigation examined the reinforcing effects and mechanisms of polypropylene fiber (PF) on the physical and mechanical properties of concrete. Scanning electron microscope (SEM) was used to observe the crystal structures and that at the aggregate-cement interfacial transition zone. Physical and mechanical tests were performed to measure the effects of PF on improving concrete's engineering properties. Results indicate that PF significantly alters the microstructure of concrete, reduces the crystallization and orientation of Ca(OH)₂, and decreases micro-voids. Specifically, PF forms a network that restricts the growth of Ca(OH)₂, bridges cracking, and reallocates stresses. PF has reduced the amount and size of crystalline, and the micro-cracking at the aggregate-cement interfacial transition zone. As a result, PF has effectively improved concrete's compressive strength, flexural strength, bonding strength, dynamic performance, and fatigue life, while reduced the water penetration and abrasion mass loss. Results also indicate that a PF content of 0.9 kg/m³ has the optimum concrete performance output for the materials used in this study.     

Abrasion resistance and mechanical properties of high-volume fly ash concrete

The abrasion resistance and mechanical properties of concrete containing high-volume fly ash (HVFA) were investigated. Sand (fine aggregate) was replaced with 35, 45, and 55% of Class F fly ash by mass. The water to cement ratio and the workability of mixtures were maintained constant at 0.46 and 55 ± 5 mm respectively. Properties examined were compressive strength, splitting tensile strength, flexural strength, modulus of elasticity and abrasion resistance expressed as depth of wear. Test results indicated that replacement of sand with fly ash enhanced the 28-day compressive strength by 25–41%, splitting tensile strength by 12–21%, flexural strength by 14–17%, and modulus of elasticity by 18–23% depending upon the fly ash content, and showed continuous improvement in mechanical properties up to the ages of 365 days. Replacing fly ash with sand significantly improved the abrasion resistance of concrete at all ages. Strong correlation exists between the abrasion resistance and each of the mechanical properties investigated.     

CTH: A three-dimensional shock wave physics code

CTH is a software system under development at Sandia National Laboratories Albuquerque to model multidimensional, multi-material, large deformation, strong shock wave physics. One-dimensional recti-linear, cylindrical, and spherical meshes; two-dimensional rectangular, and cylindrical meshes; and three-dimensional rectangular meshes are currently available. A two-step Eulerian solution scheme is used with these meshes. The first step is a Lagrangian step in which the cells distort to follow the material motion. The second step is a remesh step where the distorted cells are mapped back to the Eulerian mesh.

CTH has several models that are useful for simulating strong shock, large deformation events. Both tabular and analytic equations of state are available. CTH can model elastic-plastic behavior, high explosive detonation, fracture, and motion of fragments smaller than a computational cell. The elastic-plastic model is elastic-perfectly plastic with thermal softening. A programmed burn model is available for modelling high explosive detonation. The Jones-Wilkins-Lee equation of state is available for modelling high explosive reaction products. Fracture can be initiated based on pressure or principle stress. A special model is available for moving fragments smaller than a computational cell with statistically the correct velocity. This model is very useful for analyzing fragmentation experiments and experiments with witness plates.

CTH has been carefully designed to minimize the dispersion present in Eulerian codes. It has a high-resolution interface tracker that prevents breakup and distortion of material interfaces. It uses second order convection schemes to flux all quantities between cells.

This paper describes the models, and novel features of CTH. Special emphasis will be placed on the features that are novel to CTH or are not direct generalizations of two-dimensional models. Another paper by Trucano and McGlaun (1989) describes several hypervelocity impact calculations using CTH.     

Development of an accelerated abrasion test apparatus with a standardized testing procedure

Depending on the nature of the working environment, the abrasive wear of concrete floor slabs can range from scratching or scuffing to impact and local crushing. To assess abrasion resistance it is, therefore, necessary to have a versatile apparatus. This investigation describes the development of a basic apparatus with three modes of action and a standardized testing procedure, for assessing the abrasion resistance of concrete slabs in the industrial environment. It consisted of a rotating plate carrying a total load of 65 kg so that it was sufficiently portable for both laboratory and site testing. Three different types of abrasion head—(a) revolving pads, (b) rolling wheels, (c) dressing wheels—could be fixed to the plate so that the effects of different modes of wear could be assessed. The abrasion resistance is expressed in terms of the depth of the groove produced by 15 min of abrasion. A laboratory programme was undertaken to assess the apparatus and test method. The factors examined included the methods of assessing the abrasive wear, the duration of the test, the minimum number of tests to reliably assess the abrasion resistance, the relative performance of the three types of test head and the mechanism(s) by which each head abraded the concrete surface. Consequently a standardized procedure was developed which was found to be sensitive to variations in surface conditions. This has the additional advantages of simulating service conditions and of being repeatable, easy to follow and with the cost and time of testing not being excessive.     

Exploring the role of shear in oblique impacts: A comparison of experimental and numerical results for planar targets

Oblique impacts produce asymmetric damage patterns due to asymmetric, directed shock waves; these patterns are seen for both laboratory and planetary scale craters [1] and [2]. Previous laboratory and computational studies of impact-induced damaged have focused mainly on tensile failure following hypervelocity impacts. Though extension plays a significant role in impact-induced damage, it is widely accepted that shear failure also occurs during hypervelocity impacts. Shear failure occurs over a variety of scales both during and after impacts [3], [4] and [5]. Here we examine this process in more detail for oblique impacts. Experiments not only provide a general view of small-scale processes (including damage patterns in their final form), but also can be difficult to relate to larger impacts with confidence, even though similarities can be documented [e.g. 1]. Detailed computer models provide complementary information. Although they detail underlying processes during crater formation, they do not always contain adequate constitutive models, thereby requiring simplifying assumptions. A comprehensive model taking into account deformation following failure of rocks is still unavailable, which limits conclusions based solely on numerical simulations. Consequently, a combination of models and experiments must be used. Impact experiments into planar polymethylmethacrylate (PMMA) targets at small scale are examined in an attempt to constrain the sequence, location and style of failure. Two- and three-dimensional CTH models (with identical conditions to the experiments) were computed using a variety of failure criteria in order to determine the parameter set that best matches the experimental results. High-speed imaging recorded the sequence and location of failure within various PMMA targets, which was then compared with results from theoretical models. The CTH models provide critical details about specific failure style and indicate only minimal failure due to extension following the impact except for tensile failure at the base of the block. Instead, shear failure dominates below the crater. While the CTH hydrocode models generally match the extent of the damaged region, some differences remain. Projectile properties (density, composition, size) for impacts with the same kinetic energy affect the extent, style, and growth of damage in a given target. This includes differences in degree of uprange damage, subarcuate fractures, and sub-parallel failure planes. Comparisons between experiment and hydrocode results reveal that projectile failure (even at hypervelocity) contributes to the observed differences.     

Time-resolved penetration into glass: Experiments and computations

The penetration behavior of tungsten-alloy long-rod penetrators into glass targets is investigated and contrasted at two impact velocities, 1.25 km/s and 1.70 km/s. Penetration depths and residual rod lengths were measured by means of a 600-kV flash X-ray system at different times during penetration. The wavecode CTH was used to simulate numerically the experiments using a Drucker–Prager constitutive model, where the constitutive constants were determined from independent characterization experiments. The numerical results are compared to the experimental data and good agreement is shown.     

道面再生混凝土试验研究

采用掺加优质粉煤灰和高效外加剂的技术路线,进行了机场道面再生混凝土的强度、抗冻性、抗渗性和耐磨性等试验研究。结果表明：所配制的道面再生混凝土性能优于普通道面混凝土,满足机场道面要求,较普通道面混凝土,抗折强度提高4～11％;抗冻等级提高100％;抗渗等级提高300％以上;耐磨性提高18-36%。     

Assessing abrasion performance of self-consolidating concrete containing synthetic fibers using acoustic emission analysis

The key objective of this investigation was to evaluate the abrasion resistance of self-consolidating concrete (SCC) with and without synthetic fibers (SynFs). The abrasion resistance of normal concrete was also investigated in this study for comparison. The abrasion test was performed on concrete specimens according to the rotating-cutter method along with continuous monitoring of acoustic emission (AE) using attached AE sensors. The effects of changing concrete type and incorporating various types (flexible and semi-rigid) and lengths of SynFs on the abrasion behaviour were investigated with the aid of AE analysis. AE signal characteristics such as amplitude, signal strength, number of hits, and duration were gathered during testing. Furthermore, the collected AE data was used to complete b-value analysis as well as intensity analysis resulting in three additional parameters: b-value, severity (S_r), and historic index (H(t)). The results showed that the AE parameters were directly correlated with the abrasion damage in all tested mixtures. Adding SynFs to all SCC mixtures enhanced their abrasion resistance. The flexible fibers variety exhibited better abrasion performance on average than the semi-rigid fibers. Meanwhile, longer fibers showed lower abrasion resistance than the shorter ones with the same type. The results also indicated that AE intensity analysis was able to determine the ranges for H(t) and S_r that identify the extent of damage due to abrasion of SynF-reinforced SCC.     

Penetration into semi-infinite reinforced-concrete targets with spherical and ogival nose projectiles

We developed an engineering model for forces on rigid, spherical and ogival nose projectiles that penetrated semi-infinite, reinforced-concrete targets. Post-test target observations and triaxial, material-test data on samples cored from concrete targets guided the model development. The spherical, cavity-expansion approximation simplified the target analysis, and closed-from penetration equations were derived. The model predicted depths of penetration that were in reasonable agreement with penetration data.     

Erosive and abrasive wear resistance of overlay coatings

In the paper, the erosion and abrasion resistance of PTA, TIG and flame deposited coatings was investigated. Hardness of coatings has almost no effect on erosion resistance and incubation period. Microstructure of coatings has significant effect on erosive wear of coatings. No significant correlation was found between results of abrasive and erosive tests. Statistically significant correlation was found between erosive wear intensities determined in tests carried out at similar angles, the total content of B and C correlates with mass loss in abrasion test and erosive wear intensity at normal incidence. Laboratory tests with model abrasives cannot be used as a guide for material selection in industry.     

Generation of urban road dust from anti-skid and asphalt concrete aggregates

Road dust forms an important component of airborne particulate matter in urban areas. In many winter cities the use of anti-skid aggregates and studded tires enhance the generation of mineral particles. The abrasion particles dominate the PM10 during springtime when the material deposited in snow is resuspended. This paper summarizes the results from three test series performed in a test facility to assess the factors that affect the generation of abrasion components of road dust. Concentrations, mass size distribution and composition of the particles were studied. Over 90% of the particles were aluminosilicates from either anti-skid or asphalt concrete aggregates. Mineral particles were observed mainly in the PM10 fraction, the fine fraction being 12% and submicron size being 6% of PM10 mass. The PM10 concentrations increased as a function of the amount of anti-skid aggregate dispersed. The use of anti-skid aggregate increased substantially the amount of PM10 originated from the asphalt concrete. It was concluded that anti-skid aggregate grains contribute to pavement wear. The particle size distribution of the anti-skid aggregates had great impact on PM10 emissions which were additionally enhanced by studded tires, modal composition, and texture of anti-skid aggregates. The results emphasize the interaction of tires, anti-skid aggregate, and asphalt concrete pavement in the production of dust emissions. They all must be taken into account when measures to reduce road dust are considered. The winter maintenance and springtime cleaning must be performed properly with methods which are efficient in reducing PM10 dust.