微机模拟法研究纤维增强金属基复合材料拉伸断裂过程

A COMPUTER-SIMULATION STUDY ON TENSILE FRACTURE PROCESS IN A UNIDIRECTIONAL FILAMENTARY METAL-MATRIX COMPOSITE

本研究在统计分析及材料断裂力学分析的基础上,建立了长纤维增强金属基复合材料板材拉伸断裂过程的微计算机模拟方法。用该方法得到的模拟结果与已有实测结果吻合良好,从而初步证实了分析模型及其模拟程序系统的有效性。

The mechanical property test on a metal-matrix composite (MMC) requires a high degree of statistical reliability in its experimental data due to the structural peculiarity of the material, hence a great number of specimens. This requirement, on the other hand, implies a high cost for the test considering the cmplexity in fabricating the material. It is, consequently, desirable that an economical method should be found to analyse and evaluate the mechanical properties, especially the fracture behavior, of MMC.Computer-simulation, as such an answer,was used in the present investigation to probe the fracture process of a unidirectional fibre-reinforced MMC in tension of a two-dimensional sheet with tensile axis parallel to the fibres. The key stage of the simulation was to establish an analytical model on which the computer program was based. The model combined fracture mechanics with statistics. It mainly consisted of the distribution of a fibre's ultimate strength, the statistical sequence for simulation and the stress intensification ahead of a broken fibre. Weibull's Distribution Function of probability was found to be a valid function in demonstrating the scattering character of the fibre's ultimate strength. And, Monte Carlo's Statistical Testing Method was utilized and extended to generate a stochastic sequence for distributing the strength value and forming the simulation sequence.On the basis of the above model, a microcomputer program was accomplished to simulate the fracture process. The underlying principle of the program can be outlined as follows'divide the specimen into MxN units, i. e. , N unidirectional fibres, each with M links; assuming the Weibull distribution, generate strength values; allot the values among the fibres following the Monte Carlo testing sequence; for a given load (strain), compare the load with a fibre's (unit's) strength to decide whether the fibre fractures; in the case of fracture of any fibre, calculate the stress intensification factor around the fibre; regulate the stress field and check for fractured fibres again; increase load (strain) level and repeat the process 'searching' for fracture of fibres until gross fracture of the specimen occurs. The gross fracture refers to a condition in which N fractured units can coalesce one another in that the longitudinal distance between any two adjacent units is within half of the critical length for reinforement.The simulation test was conducted in an IBM-PC microcomputer. The result shows that both ths stress at fracture and. the fracture morphology (judged by roughness) were well in accordance with the practically measured data for a boron/aluminum composite. Therefore, the analytical model as well as the computer program built on it is effective in analysing the tensile fracture behavior of fibre-reinforced MMC under the condition of the present study. Further studies, however, is needed to extend the applicable field of the method.