• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.3
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• pp.273-279
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• 2011

The yield strength of particle-reinforced composites increases as the size of the particle decreases. This kind of length scale has been mainly attributed to the geometrically necessary dislocation punched around the particle as a result of the mismatch of the thermal expansion coefficients of the particle and the matrix when the composites are cooled down after consolidation. In this study, two dislocation-punching theories that can be used in continuum structural modeling are assessed numerically. The two theories, presented by Shibata et al. and Dunand and Mortensen, calculate the size of the dislocationpunched zone. The composite yield strengths predicted by finite element analysis were qualitatively compared with experimental results. When the size of the particle is less than $2{\mu}m$, the patterns of the composite strength are quite different. The results obtained by Shibata et al. are in qualitatively better agreement with the experimental results.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.7
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• pp.745-751
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• 2011

This study proposes finite element modeling of dislocation punching at cooling after consolidation in order to calculate the strength of particle-reinforced aluminum composites. The Taylor dislocation model combined with strain gradient plasticity around the reinforced particle is adopted to take into account the size-dependency of different volume fractions of the particle. The strain gradients were obtained from the equivalent plastic strain calculated during the cooling of the spherical unit cell, when the dislocation punching due to CTE (Coefficient of Thermal Expansion) mismatch is activated. The enhanced yield stress was observed by including the strain gradients, in an average sense, over the punched zone. The tensile strength of the SiCp/Al 356-T6 composite was predicted through the finite element analysis of an axisymmetric unit cell for various sizes and volume fractions of the particle. The predicted strengths were found to be in good agreement with the experimental data. Further, the particle-size dependency was clearly established.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2009.04a
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• pp.18-20
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• 2009

입자 강화 복합재료 내에서의 다양한 손상 메커니즘은 복합재료의 전체 거동을 예측에 상당한 영향을 미친다. 이에 본 연구에서는 입자 강화 복합재료 내에서의 누적 손상을 고려한 미세역학 기반 탄소성 모델(Kim and Lee, 2009)을 소개하고자 한다. Kim and Lee (2009)에 의해서 입자 강화 복합재료의 탄소성 모델을 위해 입자 강화 복합재료 내 계면에서의 누적 손상 및 기지재의 연성 거동이 고려되었다. 제안된 모델을 이용한 입자 강화 복합재료의 탄소성 거동 예측값은 관련된 실험값 (Llorca et al., 1991)과의 비교를 통해 수치해석을 수행하였다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.275-282
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• 2014

Particle-reinforced metal matrix composites exhibit a strengthening effect due to the particle size-dependent length scale that arises from the strain gradient, and thus from the geometrically necessary dislocations between the particles and matrix that result from their CTE(Coefficient of Thermal Expansion) and elastic-plastic mismatches. In this study, the influence of the size-dependent length scale on the particle-matrix interface failure and ductile failure in the matrix was examined using finite-element punch zone modeling whereby an augmented strength was assigned around the particle. The failure behavior was observed by a parametric study, while varying the interface failure properties such as the interface strength and debonding energy with different particle sizes and volume fractions. It is shown that the two failure modes (interface failure and ductile failure in the matrix) interact with each other and are closely related to the particle size-dependent length scale; in other words, the composite with the smaller particles, which is surrounded by a denser dislocation than that with the larger particles, retards the initiation and growth of the interface and matrix failures, and also leads to a smaller amount of decrease in the flow stress during failure.

• Composites Research
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• v.26 no.6
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• pp.355-362
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• 2013

Carbon particle based nanocomposites have been studied. Nanocomposites containing CNT and graphite particles were manipulated by aligning the micro/nano-size particles with electric field. Electric field is applied to the suspension of epoxy matrix and particulate inclusions in order to align them along the direction of the electric field. Particles aligned in a uniform direction act as a fiber in a CFRP composite. The mechanical strength and physical characteristics highly depend on particles' distribution pattern and amount. In this study, the characteristics of radioactive barrier are emphasized, which has been rarely discussed in the literature. A number of sample coupons were tested to verify their performance. The procedure of manufacturing nanocomposites by means of extremely small size particle alignment is presented in sequence. Several physical and structural performances of composites containing aligned and randomly distributed particles were compared. The results show particle alignment is very effective to enhance directional strength and radioactive barrier performance.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.27-27
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• 2003

무가압침투법으로 제조된 부피분율 10~24% SiC, TiC, B$_4$C 탄화물 입자강화 7075 Al 합금 기지 복합재료의 건식 미끄럼 마멸거동을 강화입자의 종류, 크기 및 부피 분율을 변수로 연구하였다. 미끄럼 마멸 시험은 pin-on-disk 형태의 마멸 시험기를 사용하여, AISI 52100 베어링강을 상대재로 상온 대기 중에서 실시되었다. 마멸특성의 분석과 마멸기구의 규명을 위하여 마멸면과 마멸단면을 SEM, EDS를 이용하여 분석하였다. 제조된 복합재료의 압축 시험을 통하여 측정된 항복강도와 가공경화지수는 서로 반비례하였고, 각 시편간의 경도 차는 크지 않았다. 마멸 시험결과, 크기 및 부피 분율이 7$\mu\textrm{m}$ !0%인 SiC 입자로 강화된 복합재료를 제외하고, 전체 복합재료 시편은 7075 Al 기지 합금에 비해 낮은 마멸 속도를 보였다. 10N 이하의 저하 중에서는 강화상의 종류와 상관없이 복합재료는 낮은 마멸 속도를 보였고, 25N 이상의 고하중에서는 TiC 입자강화 복합재료가 가장 낮은 마멸 속도를, SiC 입자강화 복합재료가 가장 높은 마멸 속도를 나타내었다. 강화 입자의 크기 및 부피 분율이 동일한 경우 SiC 입자로 강화된 복합재료가 가장 낮은 내마멸성을 나타내었다. 강화상의 크기 및 부피 분율이 증가함에 따라 미소 마멸에서 격렬 마멸로의 천이 하중이 증가하였다.

• Korean Journal of Materials Research
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• v.6 no.12
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• pp.1199-1212
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• 1996

본 연구는 주조성, 내압성, 내열성 등이 우수하여 군용 및 민수용 기계소재로 이용되고 있는 AI-Si-Mg계 AC4C 합금에 세라믹(AI2O3, AI2O3-TiC)을 강화시키는 복합재료제조에 관한 기초연구의 일환으로 수행하였다. 연구내용은 세라믹 강화재의 젖음성을 높이기 위하여 수소환원법에 의한 AI2O3입자의 Ni 피복과 기존의 프리폰 제조방법보다 간단하고 경제적인 자전연소합성법에 의해 AI2O3-TiC 다공성 pellet을 제조하여, 이들 강화재와 AC4C 기지금속을 이용하여 고대-compocasting 및 squeeze casting법으로 복합재료를 제조하고 미세조직, 계면생성물, 기계적 성질, 내마멸성 등의 특성을 조사하였다. 고대-compocasting법에 의해 제조된 AI2O3Ni 입자 강화 복합재료에서 강화재들은 응집체로 존재하지 않고 비교적 균일하게 분산되었고 AI2O3-TiC 강화재를 이용하여 squeeze casting으로 가압주조 하므로써 기지금속과 강화재의 젖음성이 향상되었다.

• Korean Journal of Materials Research
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• v.5 no.7
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• pp.765-774
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• 1995

The hot deformation behaviour of particulate reinforced aluminium 6061 Al composite were investigated by hot compression tests in the temperature range from 623K to 823K with strain rate of 10$^{-3}$ ~5.0 S$^{-1}$ . The effect of reinforced particulate volume fraction, mean diameter on the high temperature flow stress has also been studied. Experimental results showed that the increase in the volume fraction of reinforcement contributed to the rising of yield stress, but the stress above the yield point appeared to be steady state at all volume fractions. The apparent activation energy for deformation was 290KJ/mo1 for unreinforced 6061 Al, 327KJ/mo1 for 6061 Al-20vo1.% SiC composite and 531KJ/mo1 for 6061 Al-20vo1.%A1$_2$O$_3$composite. It appeared that $Al_2$O$_3$reinforced composites was more difficult to hot deform.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.2
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• pp.187-194
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• 2012

The strength of particle-reinforced metal matrix composites is, in general, known to be increased by the geometrically necessary dislocations punched around a particle that form during cooling after consolidation because of coefficient of thermal expansion (CTE) mismatch between the particle and the matrix. An additional strength increase may also be observed, since another type of geometrically necessary dislocation can be formed during extensive deformation as a result of the strain gradient plasticity due to the elastic-plastic mismatch between the particle and the matrix. In this paper, the magnitudes of these two types of dislocations are calculated based on the dislocation plasticity. The dislocations are then converted to the respective strengths and allocated hierarchically to the matrix around the particle in the axisymmetric finite-element unit cell model. The proposed method is shown to be very effective by performing finite-element strength analysis of $SiC_p$/Al2124-T4 composites that included ductile failure in the matrix and particlematrix decohesion. The predicted results for different particle sizes and volume fractions show that the length scale effect of the particle size obviously affects the strength and failure behavior of the particle-reinforced metal matrix composites.

• Journal of the Korean Society of Propulsion Engineers
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• v.18 no.5
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• pp.29-34
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• 2014

Particulate reinforced composite is composed of hard particles and polymer matrix. This material has been widely applied for engineering industry such as automobile, construction and aerospace. For the safe application, it is important to assess crack resistance behavior. Especially in aerospace industry, crack could cause significant problem when the material is used for solid rocket fuel. Therefore, it is inevitable to estimate the characteristics of the crack propagation. In this study, crack propagation tests were conducted using particulate reinforced composite under crosshead rate 2.54 mm/min in the range of temperature $-60^{\circ}C$ to $60^{\circ}C$. The strain contour of surface for specimen was generated using digital image correlation method.