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This study conducted pin disc friction and wear performance tests on polyethylene-lined oil pipes and four types of centralizing materials (45# steel, nylon, polytetrafluoroethylene (PTFE), and surface alloy coating) in oil fields. The friction coefficient and wear rate were tested, and the wear mechanism was analyzed using scanning electron microscopy (SEM) and three-dimensional confocal microscopy. Using a combination of experimental testing analysis and theoretical research, a comprehensive evaluation of the current wellbore centering and anti-wear technology for oil was conducted. The experimental results indicate that the usage limit of polyethylene-lined oil pipes is 400 N, and compared to metal oil pipe materials, the wear rate of both stabilizing material and tubing material is lower, indicating that it has a certain service life. From the perspective of testing load, taking into account the factors of friction coefficient and wear rate, the recommended sequence of straightening material for polyethylene lined oil pipes is (1) surface alloy coating, (2) nylon, (3) PTFE, and (4) 45# steel.

The necessity of incorporating the Lode angle into a fracture criterion in predicting ballistic resistance of ductile metal plates has not been well elucidated so far although the ductility of a metal may be Lode dependent. In this paper, 4.0 mm thick Weldox 700 E steel plates were fired by 5.95 mm diameter blunt rigid projectiles in a one-stage gas gun in the impact velocity range of 141.2 m/s∼275.7 m/s. A failure mode of shear plugging was observed in the test and the ballistic limit was obtained by fitting the initial-residual velocity data. An axisymmetric finite element (FE) model corresponding to the test was built in ABAQUS and then was utilized to predict the ballistic resistance and fracture behavior of the targets. In the FE model, a slightly modified Johnson-Cook constitutive relation was companied by either a Lode independent modified Johnson-Cook (MJC) or the Lode dependent modified Mohr–Coulomb (MMC) fracture criterion. The plasticity and fracture of the metal were fully calibrated by a series of mechanical tests under varying stress states, strain rates and temperatures. According to the tests and parallel FE simulations, it was found that the fracture of Weldox 700 E is obviously Lode dependent. However, ballistic simulations using the MMC and MJC fracture criterion predicted very close ballistic limit velocity and similar shear plugging failure mode when compared with the test results. The dominant stress state of the material failed in the process of shear plugging was revealed by detailed FE analysis and it was found that the ductility of the metal is quite different on the dominant stress state according to the two fracture criteria. To interpret the current simulation results, further FE simulations were carried out on fictitious metals and it was found that for less ductile metallic plates the MMC fracture criterion predicts a much lower ballistic limit velocity (as much as 22%) when compared with the simulation result from the MJC fracture criterion. In contrast, for metal plates with high ductility, the simulations from the two different fracture criteria would produce quite close ballistic limit velocity predictions.

The majority of current finite element (FE) simulations on shear plugging adopted Lode independent fracture criteria, and the value of utilizing a Lode dependent fracture criterion in predicting the ballistic resistance of metallic plates undergoing shear plugging has not been well understood. A group of 12.65 mm diameter blunt rigid projectiles were fired against 9.94 mm thick 2024-T351 aluminum alloy plates by using a one-stage gas gun in the impact velocity range of 133.4 m/s∼363.8 m/s. A failure mode of Shear plugging was observed in the test and the ballistic limit was obtained by fitting the initial and residual velocity data. A 3D FE model corresponding to the test was built in ABAQUS and then was adopted to predict the ballistic resistance and fracture behavior of the target. In the simulations, a slightly modified Johnson–Cook constitutive relation was companied with either the Lode dependent Modified Mohr–Coulomb (MMC) fracture criterion or the Lode independent original Johnson-Cook fracture criterion. It was found that the FE model using the MMC fracture criterion predict the ballistic limit and shear plugging behavior in good accordance with that obtained in the tests. In contrast, the simulations using the Johnson–Cook fracture criterion over-predicted the ballistic limit by 28.5% although the shear plugging failure pattern was reasonably predicted. Detailed analysis shows that the dominant stress state of the material in the shear plugging band is nearly shear, where the Lode angle has an obvious influence to reduce the fracture strain of the metal comparing with axial symmetric conditions. FE simulations by using fictitious metals with the same fracture data at axial symmetry tension but different fracture stain at shear also confirm that the ballistic resistance of a metal plate is much dependent on the effect of the Lode angle on a material's ductility.

Recent investigations have shown that the ductility of a metal may depend on not only the stress triaxiality but also the Lode parameter, especially in the relatively low stress triaxiality range. However, applications using the Lode dependent fracture criterion are few and the value of incorporating the Lode parameter into a fracture criterion to predict impact related fracture is poorly understood. In the present paper, Taylor impact test by using 2024-T351 aluminum alloy rods of 5.95 mm diameter and 29.75 mm length was firstly conducted in a one-stage gas gun in the impact velocity range of 110.8–312.7 m/s. Mushrooming and shear cracking were observed in the test with increasing impact velocity. Subsequently, mechanical tests were conducted in a universal testing machine and a SHPB test facility. By using a hybrid experiment–numerical method, a modified version of Johnson–Cook strength model, a Lode-dependent fracture criterion as well as the Johnson–Cook (JC) fracture criterion were calibrated. Finally, 3D FE model corresponding to the test was built in ABAQUS and then was adopted to predict the shear cracking of the Taylor rods. It was found that FE simulations by using the Lode dependent fracture criterion give reasonable fracture pattern predictions while that using the Johnson–Cook fracture model obviously underestimates the fracture behavior. Detailed analysis shows that the dominant stress state of the material in the projectile's fracture region in the impact event is in the range where the Lode parameter has an obvious influence on the metal's ductility. FE simulations by using virtual metals also show that the Taylor impact fracture behavior prediction is much dependent on the effect of the Lode parameter on a material's ductility.

Recent studies showed that the ductility of some metals was affected by not only stress triaxiality but also Lode angle parameter. However, the majority of impact-related simulations used Lode independent fracture criteria. The necessity of incorporating Lode angle parameter into a fracture criterion in predicting ballistic impact behavior of monolithic 2024-T351 aluminum alloy (AA2024-T351) plates has been previously addressed in the work of Xiao et al. [1] . This paper serves as an extension by considering plates with double-layered configuration and the same total thickness. Ballistic impact tests were performed on 4.82 + 4.82 mm thick double-layered plates. Blunt projectiles with dimensions of Φ 12.66×50.56 mm3 and a nominal mass of 50 g were used, and the impact velocities ranged from 133.4 to 363.8 m/s. According to the experimentally obtained data, ballistic limit velocities (BLVs) were calculated and fracture patterns of post-test plates were analyzed. It was found that for double-layered configurations, the first plate failed by shear plugging and the second plate failed by tensile stretching and global deformation. By replacing monolithic plates with double-layered ones, the BLV increased from 138.4 to 180.1 m/s, a 30% improvement in ballistic resistance. Subsequently, numerical simulations of ballistic impact tests were performed by software ABAQUS/Explicit. Mechanical property of AA2024-T351 was described by Johnson-Cook (JC) plasticity model accompanied with either the Lode independent JC fracture criterion or the Lode dependent modified Mohr-Coulomb (MMC) fracture criterion. The numerical results were compared with those obtained from experiments. It was found that MMC criterion predicted BLVs more accurately than JC criterion. The prediction errors for MMC and JC criteria were respectively 3.3% and 11.4%, with the former being merely one-third of the latter. The overall failure modes of double-layered plates were correctly predicted by both JC and MMC fracture criteria. However, details of the fracture patterns, such as the formation of fragments, the shape and number of ejected plugs, and the initiation and propagation of cracks, were better captured by MMC criterion than by JC criterion. Detailed analysis shows that the stress state governing ballistic impact tests locates in the range where Lode angle parameter is strong enough to induce a significant difference between JC and MMC criteria. Under such stress state, the ductility of AA2024-T351 is correctly predicted by the Lode dependent MMC criterion but is overestimated by the Lode independent JC criterion.

The aim of the present paper is to study the effect of shapes of projectile nose on the ballistic resistance of 6061-T651 aluminum alloy thin plates, and to evaluate the effect of Lode angle dependent fracture criterion when predicting the ballistic resistance of 6061-T651 aluminum alloy thin plates struck by projectiles with different nose shapes through finite element (FE) simulations. To this end, the ballistic impact tests are firstly conducted using different nose shapes of projectiles. Ballistic limit velocities (BLVs) of different projectile-plate pairs considered are calculated by using initial versus residual velocity data obtained from the experiments. It can be found that the BLV of spherical projectile is the highest, followed by ogival-, blunt- and hemispherical-nosed projectiles. Subsequently, a 3D FE model corresponding to the test is built by ABAQUS/Explicit software and then they are adopted to predict the ballistic resistance of the plate. In these simulations modified Johnson-Cook (MJC) strength model accompanied with either the Lode angle independent and slightly modified Johnson-Cook (MJC) fracture criterion or the Lode angle dependent and modified Mohr-Coulomb (MMC) fracture criterion are adopted to describe plate material properties. Finally, the predicted ballistic resistance of the plates is compared with those observed in the experiments. The numerical predictions of the plate struck by different nose shapes of projectiles show that the BLV predicted by Lode angle dependent MMC fracture criterion is more accurate for spherical and ogival-nosed projectile, while the BLV predicted by Lode angle independent MJC fracture criterion is more accurate for blunt- and hemispherical-nosed projectile. In addition, the results show that the Lode angle's effect is related to the curvature radius of the nose shape of projectile, i.e., the Lode angle's effect decreases with the increase of the curvature radius.

In the field of ballistics, Johnson-Cook (JC) plasticity and fracture models have provided a good theoretical basis for the prediction of ballistic performance by capturing the essence of ductile metal fracture. Nevertheless, the JC model cannot accurately reproduce the fracture behaviour of some metals. Many Lode parameter-dependent fracture criteria have effectively improved this deficiency, indicating that the fracture loci of these metals are Lode-dependent, even though the flow stress behaviour is stress state dependent, which cannot be well characterized by the JC plasticity model. In this paper, a series of mechanical tests and parallel numerical simulations of ZK61m magnesium alloy were conducted. The results showed that the flow stress behaviour and fracture loci of the alloy were obviously Lode dependent. Therefore, it seems insufficient to evaluate only the necessity of incorporating Lode parameter into a fracture criterion in predicting ballistic performance of ZK61m magnesium alloy, and more investigations on the influence of Lode parameter on the plasticity behaviour of the material should be carried out. In the present work, ballistic tests were conducted on 5 mm thick ZK61m magnesium alloy plates using blunt and ogival nose shaped projectiles with a nominal diameter of 12.68 mm. The targets failed by shear plugging when impacted by blunt-nosed projectiles, but caused a unique failure pattern under the impact of ogival-nosed projectiles. Lode-dependent plasticity model and fracture criterion were adopted. Better prediction accuracy was observed when Lode parameter is considered in both the plasticity model and fracture criterion simultaneously.

A recently developed single shear specimen (SSS) was used to investigate the thermo-viscoplastic behavior of 2024-T351 aluminum alloy (AA2024-T351) under simple shear stress state. Shear stress-shear strain relations over a wide range of strain rates, covering low (0.001 and 0.1 s−1), medium (10 s−1), high (3000 and 6000 s−1) and very high (14000-49000 s−1) regimes and at initial temperatures from 293 to 573 K were obtained experimentally. The results show that: (1) at 293 K, AA2024-T351 exhibited negligible strain rate sensitivity at strain rates below 6000 s−1, and the effect of strain rate became obvious at strain rates above 14000 s−1; (2) dynamic strain aging (DSA) occurred at temperatures between 373 and 573 K and strain rates below 6000 s−1; (3) strain rate sensitivity of the material was strongly affected by DSA, and bell-shaped strain rate sensitivity curves were observed; (4) with an increase in temperature, peak values of the bell-shaped strain rate sensitivity curves shifted to higher strain rates. A constitutive model taking the advantages of Johnson-Cook model, Khan-Huang-Liang model, Nemat-Nasser-Li model and Wang-Guo-Gao model was developed for deformation behavior description, with the effects of viscous drag on dislocation motion and DSA considered. The experimental flow stress curves were compared to the model predictions, and a good agreement was observed. To validate the constitutive model independently of the experiments used for the identification of the model parameters, numerical simulations of Taylor impact tests were performed. A good agreement between experimental and numerical post-test specimens, in terms of mushroom shaped specimen head and reduced specimen length, was observed. According to the numerical results, strain rates varied largely between 103 and 106 s−1 during Taylor impact tests. Besides, numerical simulations of Taylor impact tests were performed again using the constitutive model excluding the viscous drag component, and less accurate numerical results were obtained. It implies that for precise computations of engineering applications, the actual strain rate should be considered in the establishment of constitutive models.

To reveal the effect and necessity of introducing the Lode angle into a fracture criterion in ballistic performance simulations of metallic Plates, experimental and numerical work were carried out on 6061-T651 aluminum alloy (AA6061-T651) thick Plates. Firstly, a series of ballistic tests were conducted via a one-stage gas gun test facility that blunt-nosed projectiles of φ12.68 mm penetrated onto 20 mm thick AA6061-T651 Plates at impact velocities ranging from 280.0 m/s to 400.0 m/s. Subsequently, experimental results in terms of initial versus residual velocities of the projectiles and the failure characteristics of the Plates were reported. Experimental results showed that shear plugging was the dominating failure mode of the perforated Plates. Meanwhile, numerical results corresponding to the ballistic tests were obtained using finite element (FE) simulations via the commercial software ABAQUS/Explicit. Specially, we compared the results between simulations using a Lode dependent fracture criterion and a Lode independent. Finally, the FE simulations indicated that using a Lode dependent fracture criterion better predicts the ballistic behavior of the thick AA6061-T651 Plates under impact of blunt-nosed projectiles. It is also found that the Lode angle affects the fracture behaviour of the AA6061-T651 significantly. And this effect decreases with the increase of the materials’ ductility.

The aim of the present paper is to evaluate the effect of Lode angle incorporation into a fracture criterion when predicting the ballistic resistance of 2024-T351 aluminum alloy plates struck by cylindrical projectiles with different nose shapes through finite element (FE) simulations. To this end ballistic tests in the sub-ordnance impact velocity range were firstly conducted on 9.94 mm thick 2024-T351 aluminum alloy plates using cylindrical projectiles with blunt, hemispherical and ogival nose shapes, a nominal diameter of 12.66 mm, and a nominal mass of 50 g. Ballistic limit velocities (BLVs) for different projectile-target pairs considered were calculated using initial vs. residual velocity data obtained in the experiments. Subsequently FE simulations of the conducted experiments were performed with SIMULIA Abaqus software. In those simulations Johnson–Cook yield criterion with a modified strain hardening law was accompanied with either the Lode-independent Johnson–Cook (JC) fracture criterion or the Lode-dependent modified Mohr–Coulomb (MMC) fracture criterion to describe target material properties. Finally, the predicted ballistic resistance and fracture patterns of the targets were compared with those observed in the experiments. It was found that in the simulations with the Lode-independent JC fracture criterion the BLVs of the targets were overestimated by 18.0–35.1% depending on the projectile nose shape. In the simulations with MMC fracture criterion the BLVs predictions were substantially improved, so that the difference with the experimental results did not exceed 9.0%. Targets failure mechanisms obtained in the simulations with MMC fracture criterion also better match the experiments than those predicted with JC fracture criterion. In the simulations with MMC fracture criterion the targets impacted by the projectiles with blunt and hemispherical noses failed through shear plugging, whereas ogive-nosed projectiles caused ductile hole enlargement and target fragmentation due to its rear side radial fracture and bending of formed short petals with their eventual shear fracture. At the same time the simulations with JC fracture criterion predicted shear plugging for the blunt-nosed projectiles, very small conical plug ejection and target fragmentation due to discing for the hemispherical-nosed projectiles, and ductile hole enlargement for the ogive-nosed projectiles. A detailed analysis of the failure process revealed that in the case of the ogive-nosed and hemispherical-nosed projectiles, respectively, the ductile hole enlargement occurs during the initial stage of the impact and subsequent through-thickness fracture develops causing either fragmentation of the target or its shear plugging failure. The Lode-independent JC fracture criterion overestimates a material fracture strain under shear, thus leading to poor prediction of 2024-T351 aluminum alloy targets ballistic performance in the numerical simulations.

In the present study, high-speed horizontal water entry behaviors of flat, ogival and hemispherical-nose projectiles were studied experimentally and theoretically. Particular attention is given to characterizing the projectile dynamics and the cavity evolution before a deep pinching starts. An analytical cavity model based on the solution to the Rayleigh–Besant problem was developed to describe the cavity dynamics of projectile water entry. Three parameters in the cavity model were discussed and determined theoretically and experimentally. Numerical simulations using the AUTODYN-2D Lagrange–Euler coupling techniques were conducted to specially study the drag coefficients of projectiles. Based on the experimental and numerical results, a drag coefficient model independent on the cavitation number was proposed. The results indicated that there are two variation laws for the three parameters in the cavity model; Additionally, the drag coefficients increase with the impact velocities with holding the projectile nose constant and decrease with an increase in the projectile nose coefficient (CRH) value. Good agreements were observed between analytical results and experimental observations.

The present paper presents an experimental and numerical study concerning the deformation and failure behavior in the Taylor impact test. Projectiles manufactured from a commercial high strength and super-hard aluminum alloy 7A04-T6 with a nominal diameter of 12.6 mm and a length of 50.8 mm were fired against a hardened tool steel plate by a one- and two-stage compressed gas gun within the velocity range of 175–370 m/s. Three different deformation and failure modes were observed from the test: mushrooming, shear cracking and fragmentation. Individual velocity ranges and the transitions between the deformation/failure modes are identified by both experiments and numerical simulations. Slightly modified Johnson–Cook models of strength and accumulative damage failure are employed in 3D numerical simulations to describe material behavior of the striking cylinders. Good agreement between the numerical simulations and the experimental results was found. Detailed computational results of each scenario are offered to understand the deformation and failure mechanisms.

The ballistic perforation performance of a kinetic energy projectile would be much more influenced by the projectile’s deformation during the impact process. A projectile may suffer from large deformation and even fracture as more and more advanced materials are used as resistant components. A comparison investigation was presented in this study concerning the deformation and fracture behavior of kinetic energy projectiles manufactured from 38CrSi steel of two different hardness values. Flat-nosed projectiles were fired in a two-stage compressed gun test facility against hard steel plates within the velocity range of 200–600 m/s. The impact process was monitored by a high-speed camera. Experimental results showed that, for the soft projectiles there are three deformation and fracture modes, i.e., mushrooming, shear cracking and petalling, and that for the hard projectiles there are also three modes, mushrooming, shearing cracking and fragmentation.

This note is specifically concerned with cracks emanating from a surface semi-spherical cavity in an infinite body (see Fig. 1 ) by using the boundary element software FRANC3D developed by a fracture mechanics investigation group of Cornell University. The numerical results can reveal the effect of the geometry of the surface cavity on the stress intensity factors.

This note is concerned with a surface semi-circular crack by using the fracture analysis software FRANC3D developed by a fracture mechanics investigation group of Cornell University. Attention is specifically paid to the effect of the boundaries parallel to the crack on the stress intensity factors (SIFs).

Taylor impact test presented in a previous study on a commercial high strength and super hard aluminum alloy 7A04-T6 are numerically evaluated using the finite element code ABAQUS/Explicit. In the present study, the influence of fracture criterion in numerical simulations of the deformation and fracture behavior of Taylor rod has been studied. Included in the paper are a modified version of Johnson-Cook, the Cockcroft-Latham(C-L), the constant fracture strain, the maximum shear stress and the maximum principle stress fracture models. Model constants for each criterion are calibrated from material tests. The modified version of Johnson-Cook fracture criterion with the stress triaxiality cut off idea is found to give good prediction of the Taylor impact fracture behavior. However, this study will also show that the C-L fracture criterion where only one simple material test is required for calibration is found to give reasonable predictions. Unfortunately, the other three criteria are not able to repeat the experimentally obtained fracture behavior. The study indicates that the stress triaxiality cut off idea is necessary to predict the Taylor impact fracture.

The water entry problem is considered as a classic problem which has a research history of more than 70 years, the water‐entry process for projectiles with different nose will be significant for related application and experimental design. In this paper, a series of numerical simulations were conducted to study the water‐entry behaviors of cylindrical, hemispherical and conical projectiles using the coupled Lagrange‐Euler technology in the non‐linear finite element code AUTODYN‐2D. The detailed cavity expansion process and the cavity characteristics of three projectiles in the early stages of water‐entry were obtained. The effects of the projectile nose shape and the projectile velocity on the cavity shapes were studied. Simultaneously, the laws of velocity attenuations for three projectiles were also proposed in this study. The results show that cylindrical projectile has the minimum ratio of the cavity length to the cavity half thickness among the three projectiles when they have identical impact velocities and the smoothed nose shape of projectiles can help reduce the water resistance, thus slowing down the velocity attenuations.