李玉龙
飞机结构的抗鸟撞设计与分析、鸟撞试验动响应测试方法、纤维增强混杂复合材料、陶瓷颗粒增强金属基复合材料、陶瓷增强功能梯度防护装甲的优化设计与制造、非晶态金属材料、形状记忆合金以及多种金属材料等的动态响应、本构方程、变形机理、破坏机制与材料微细观结构的关系;材料和结构动态特性,包括动态断裂特性的实验测试方法等
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- 姓名:李玉龙
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学术头衔:
博士生导师
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学科领域:
林业工程
- 研究兴趣:飞机结构的抗鸟撞设计与分析、鸟撞试验动响应测试方法、纤维增强混杂复合材料、陶瓷颗粒增强金属基复合材料、陶瓷增强功能梯度防护装甲的优化设计与制造、非晶态金属材料、形状记忆合金以及多种金属材料等的动态响应、本构方程、变形机理、破坏机制与材料微细观结构的关系;材料和结构动态特性,包括动态断裂特性的实验测试方法等
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李玉龙, Fenghua Zhou, Jean-Francois Molinari *, Yulong Li
Engineering Fracture Mechanics 71(2004)1357-1378,-0001,():
-1年11月30日
The three-point bending test by Kolsky-bar apparatus is a convenient technique to test the dynamic fracture properties of materials. This paper presents detailed three-dimensional finite element simulations of a silicon particle reinforced aluminum (SiCp/Al) experiment (Li et al., [Proceedings of the US Army Symposium on Solid Mechanics]. In the simulations, the interaction between the input bar and the specimen is modeled by coupled boundary conditions. The material model includes large plastic deformations, strain-hardening and strain-rate hardening mechanisms. Furthermore, crack initiation and propagation processes are simulated by a cohesive element model. The simulation results quantitatively agree with the experimental measurements on three fronts: (1) the structural response of the specimen, (2) the time of unstable crack propagation, and (3) the local deformations at the crack-tip zone. The simulations reveal crack propagation characteristics, including crack-tip plastic deformation, crack front curving, and crack velocity profile. The effectiveness of Kolsky-bar type fracture tests is verified. It is shown that a rate-independent cohesive model can describe the complicated dynamic elastic–plastic fracture process in the SiCp/Al material.
Dynamic fracture, Numerical simulation, Cohesive element, Crack propagation
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李玉龙, Yulong Li a, , K.T. Ramesha, ∗, E.S.C. Chin b
Materials Science and Engineering A 382(2004)162-170,-0001,():
-1年11月30日
The mechanical response of a metal-matrix composite to dynamic shearing deformations has been measured, using a new design of the thin-walled tubular specimen for the torsional Kolsky bar experiment that allows working with these difficult-to-machine materials. The advantages of using the new specimen design are as follows: (i) the thickness of the thin wall along the axial direction is very uniform; (ii) specimen machining is extremely simple; (iii) the cost of specimen machining is greatly reduced. The approach has been used to characterize the high shear strain rate (103s−1) behavior of an A359/SiCp composite and its corresponding A359 monolithic alloy with the torsion Kolsky bar. The experimental results show that the flow stress of the composite in shear increases in the presence of SiC particles, whereas the failure strain is reduced. The shear failure strains of both the A359/SiCp composite and the A359 monolithic alloy appear to increase with increasing strain rate. Previous observations have shown that particle fracture develops during compressive deformations of this material. However, particle fracture is not a significant damage mode during the shearing deformations of the composite, and this is reflected in differences between the torsional and tension behaviors of the material.
Metal-matrix composites, Torsion, High-strain-rate, Shearing, Failure, Rate-dependence
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【期刊论文】The Investigation of Residual Stress Effect on Metal-ceramic Bond
李玉龙, Haitao Xin, , Yulong Li , Xuanxiang Ma , Fei Xu , Weiguo Guo
,-0001,():
-1年11月30日
Porcelain-fused-to-metal (PFM) is playing a very important role in prosthetics dentistry. The bond strengths in metal-ceramic system have been focused on, since the method of PFM was used to prosthetics. In this paper, the thermal residual stress effects on metal-ceramic bond were considered during cooling of porcelain-fused-to-metal restoration to analysis the metal-ceramic bond stresses. The ISO crack initiation test specimen (three-point flexure bond test) was simulated by finite element method. The analysis was implemented in two steps. In the first step, the porcelain was assumed as viscoelastic material (720℃-550℃), while in the second step the porcelain was as elastic body (550℃-25℃). The results show that the compressive stress caused by difference ofthermal expansion coefficients of two materials during cooling occurs in the ceramic. The shear stress induced by mechanical load is offset by thermal shear stress. The mechanical tensile stress and the thermal compressive stress normal to interface are concentrated at the end of the bond interface, but the tensile stress is much higher. It is clear that the thermal residual stresses are very important to metal-ceramic restorations, and it is greatly affected by the viscoelastic behavior of porcelain. This also indicates a higher probability of failure produced by the tensile stress rather than by shear stress.
Metal-ceramic bond, Residual stresses, Stress analysis
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李玉龙, Y. Li a, K.T. Ramesh a, *, E.S.C. Chin b
International Journal of Solids and Structures 37(2000)7547-7562,-0001,():
-1年11月30日
The mechanical behaviors of an A359/SiCp metal
Matrix composite, Aluminum alloy, Viscoplastic response
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李玉龙, Tao Suo , a, Yulong Li, b, *, , Hong Yu , c, Fei Xu , d, Zhongbin Tang , e, Lei Li , f
,-0001,():
-1年11月30日
In this paper, the mechanical behavior of acrylic polymers at elevated temperature was investigated. Four acrylic polymers were tested at high strain rate by using compression Hopkinson bar and at quasi-static strain rate by using an Instron servo hydraulic axial testing machine with the testing temperature from 218K to 393K. The results show that the mechanical property of acrylic polymers depends heavily on the testing temperature. The yield stress and Young's modulus were found to decrease with increasing temperature at low strain rate. At very low temperature, the materials display typical brittle fracture; however their plasticity improves remarkably at high temperatures. The predictions of the mechanical behavior including the effect of temperature and strain rate using a proposed theoretical model have a good agreement with experimental results.
acrylic polymer,, compression Hopkinson bar,, quasi-static,, dynamic,, fracture.,
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李玉龙, Y. LI and K. T. RAMESH
Acta mater. Vol. 46, No.16, pp. 5633-5646, 1998,-0001,():
-1年11月30日
Compressive plastic deformation of particle-reinforced metal
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【期刊论文】HIGH STRAIN RATE DEFORMATION OF MARTENSITIC NiTi SHAPE MEMORY ALLOY
李玉龙, Yong Liu, *, Yulong Li, K.T. Ramesh and Jan Van Humbeeck
Scripta Materialia, Vol. 41, No.1, pp. 89-95, 1999,-0001,():
-1年11月30日
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【期刊论文】FLOW STRESS OF F.C.C. POLYCRYSTALS WITH APPLICATION TO OFHC CU
李玉龙, SIA NEMAT-NASSER and YULONG LI†
Acta mater. Vol. 46, No.2, pp. 565-577, 1998,-0001,():
-1年11月30日
Based on the concept of dislocation kinematics and kinetics, paralleled with a systematic experimental investigation, a physically-based model is, developed for f.c.c, polycrystals, using OFHC copper for illustration. First, the concept of the motion of dislocations and the barriers that they must overcome in their motion, is used as an underlying motivation to obtain general expressions which include a number of free constitutive parameters. These parameters are then evaluated by direct comparison with experimental data. High strain-rate compression experiments are performed using UCSD's recovery Hopkinson tech-nique (see Nemat-Nasser, S., isaacs, J. B. and Starrett, J. E., Proc. R. Soc., 199l, 435A,, 371; Nemat-Nas-ser, S., Li, Y. F. and Isaacs, J. B., Mech. Mater.. 1994, 17, 111; Nemat-Nasser, S. and Isaacs, J. B., Acta Metall., 1997, 45, 907). Strains close to 100% are achieved in these tests, over a temperature range of 77-1100K, and strain rates of 10 3 to 8000 s-1; the quasi-static tests are performed using an lnstron machine. For low-temperature tests, both the as-received and annealed samples are tested. With few free constitutive parameters, good correlation between the theoretical predictions and experimental results is obtained, over the entire range of strain rates and temperatures. The orders of magnitude of several of these parameters are first estimated based on the underlying structure of the material. Experimental results are then used to tune the final values of these parameters. It turns out that the structure of the constitutive relations and the value of a number of the constitutive parameters are essentially the same for commercially pure tanta-lum (b.c.c. metal) and OFHC copper. The relation between the two cases is examined and the similarities and differences are discussed.
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【期刊论文】Dynamic characterization of layered and graded structures under impulsive loading
李玉龙, Y. Li a, K.T. Ramesh a, *, E S C. Chin b
International Journal of Solids and Structures 38(2001)6045-6061,-0001,():
-1年11月30日
Relatively thick graded and layered structures have significant potential armor applications, and have recently been manufactured with some degree of consistency. The mechanical behaviors of the individual layers within such a structure play an important role in determining the structure's resistance to impact. This work examines layered and graded plates made of metal-ceramic composites with the volume fraction of ceramic reinforcement varying through the thickness. In a previous work (Acta Mater 46 (1998) 5633), the results of high-strain-rate experiments have been used to develop a model for the viscoplastic response of metal-matrix composites of varying volume fraction. Using this model, numerical results are presented on the propagation of large amplitude stress waves through layered and graded structures. The results show that the wave propagation within layered and graded structures involves a complex coupling of elastic and viscoplastic response. It is demonstrated that the choice of gradation has great significance for impact applications.
FGM, IMPACT, Stress wave, MMC
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李玉龙, Yulong Li a, , K.T. Ramesh a, ∗, E.S.C. Chin b
Materials Science and Engineering A 371(2004)359-370,-0001,():
-1年11月30日
Acomparison is presented of the dynamic plastic deformation and tensile failure of two metal-matrix composites (one with a cast alloy matrix and the other with a wrought alloy matrix). The two composites are ceramic particle reinforced aluminum alloys: F3S.20S (A359 aluminum alloy reinforced by 20% SiC particles) and W6A20A (6061-T6 aluminum alloy reinforced by 20% Al2O3 particles). The corresponding unreinforced matrix alloys were also examined. The effects of strain rate on the tensile responses of these composites were determined using the tension Kolsky bar. The microstructures and fracture surfaces of the specimens of each composite were examined using SEM and optical microscopy. The experimental results show that the flow stresses of both composites are higher than that of their matrix alloys, whereas the composite fracture strains are lower. The fracture strains of the W6A20A composite and the 6061-T6 monolithic matrix alloy were much higher than those of the F3S20S composite and the A359 monolithic matrix alloy. Both the W6A20A composite and 6061-T6 monolithic matrix alloy behaved in a ductile manner with necking prior to fracture, while both the F3S.20S composite and A359 monolithic matrix alloy behaved in a brittle manner with no necking prior to fracture. Microscopic examination revealed tensile failure of the A359 matrix alloy and its composite to be controlled by the microcracking of Si network, which formed in the interdendritic silicon rich region, whereas failure of the 6061-T6 based composite is controlled by cracking of reinforcement particles.
Quasistatic, Microcracking, Metal-matrix composites, Dynamic
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