Functionally graded shape memory alloys: Design, fabrication and experimental evaluation

Shariat, Bashir S.,Meng, Qinglin,Mahmud, Abdus S.,Wu, Zhigang,Bakhtiari, Reza,Zhang, Junsong,Motazedian, Fakhrodin,Yang, Hong,Rio, Gerard,Nam, Tae-hyun,Liu, Yinong Elsevier 2017 Materials & Design Vol.124 No.-

<P><B>Abstract</B></P> <P>Functionally graded shape memory alloys have the advantage of combining the functionalities of the shape memory effect and those of functionally graded structures. By proper design, they can exhibit new and complex deformation behaviour that is unmatched in uniform shape memory alloys. One obvious advantage of functionally graded shape memory alloys is their widened transformation stress and temperature windows that provide improved controllability in actuating applications. This paper reports on the concept, fabrication, experimentation and thermomechanical behaviour of several designs of functionally graded NiTi alloys, including compositionally graded, microstructurally graded and geometrically graded NiTi alloys, and the various techniques that may be used to create these functionally graded materials. It is found that the property gradients created along the loading direction or perpendicular to the loading direction produce distinct thermomechanical behaviours. The property gradient along the loading direction provides stress gradient over stress-induced transformation, which can be adjusted by the property gradient profile. The property gradient through the thickness direction of plate specimens and perpendicular to the loading direction provides four-way shape memory behaviour during stress-free thermal cycling after tensile deformation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Functionally graded shape memory alloys provide widened transformation stress and temperature windows in actuation application. </LI> <LI> The property gradient was achieved in three ways: microstructural gradient, compositional gradient and geometrical gradient. </LI> <LI> Property gradients created along the loading direction or perpendicular to that direction produce distinct thermomechanical behaviours. </LI> <LI> A variety of techniques has been proposed for fabricating functionally graded shape memory alloy structures. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Experimental Measurement of Coefficient of Thermal Expansion for Graded Layers in Ni-Al₂O₃ FGM Joints for Accurate Residual Stress Analysis

Ryu, Sae-hee,Park, Jong-ha,Lee, Caroline Sunyong,Lee, Jae-chul,Ahn, Sung-hoon,Oh, Sung-tag The Japan Institute of Metals 2009 MATERIALS TRANSACTIONS Vol.50 No.6

<P>Functionally graded materials have composition gradients from one end to the other as the result of a gradual transition of the properties of different materials. The residual stress caused by the difference of coefficient of thermal expansion can be minimized using functionally graded material. Therefore, the gradient of the coefficient of thermal expansion should vary according to the compositional gradient. In this study, the coefficient of thermal expansion of each compositional layer of Ni-Al<SUB>2</SUB>O<SUB>3</SUB> functionally graded material was measured using a dilatometer. These measurements provided the material properties required to calculate the residual stress, using three-dimensional modeling for accurately predicting crack positions, since it is difficult to measure residual stress experimentally. The measurement results showed the gradual increase of the coefficient of thermal expansion from Al<SUB>2</SUB>O<SUB>3</SUB>-rich composition to Ni-rich composition. Finally, the results of calculating residual stresses using the measured coefficient of thermal expansion showed that the crack positions were predicted more accurately than those using the coefficient of thermal expansion calculated by the linear rule of mixtures. This was because the measured values include the effect of porosity of the composite, whereas the linear rule of mixtures cannot account for the porosity of each layer.</P>

A simple analytical approach for thermal buckling of thick functionally graded sandwich plates

Fouzia El-Haina,Ahmed Bakora,Abdelmoumen Anis Bousahla,Abdelouahed Tounsi,S. R. Mahmoud 국제구조공학회 2017 Structural Engineering and Mechanics, An Int'l Jou Vol.63 No.5

This study aimed to presents a simple analytical approach to investigate the thermal buckling behavior of thick functionally graded sandwich by employing both the sinusoidal shear deformation theory and stress function. The material properties of the sandwich plate faces are continuously varied within the plate thickness according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are considered as uniform, linear and non-linear temperature rises across the thickness direction. Numerical examples are presented to prove the effect of power law index, loading type and functionally graded layers thickness on the thermal buckling response of thick functionally graded sandwich.

Thermal post-buckling analysis of functionally graded beams with temperature-dependent physical properties

Turgut KOCATÜRK,Şeref Doğuşcan AKBAŞ 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.15 No.5

This paper focuses on thermal post-buckling analysis of functionally graded beams with temperature dependent physical properties by using the total Lagrangian Timoshenko beam element approximation. Material properties of the beam change in the thickness direction according to a power-law function. The beam is clamped at both ends. In the case of beams with immovable ends, temperature rise causes compressible forces and therefore buckling and post-buckling phenomena occurs. It is known that post-buckling problems are geometrically nonlinear problems. Also, the material properties (Young's modulus, coefficient of thermal expansion, yield stress) are temperature dependent: That is the coefficients of the governing equations are not constant in this study. This situation suggests the physical nonlinearity of the problem. Hence, the considered problem is both geometrically and physically nonlinear. The considered highly non-linear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton-Raphson iteration method. In this study, the differences between temperature dependent and independent physical properties are investigated for functionally graded beams in detail in post-buckling case. With the effects of material gradient property and thermal load, the relationships between deflections, critical buckling temperature and maximum stresses of the beams are illustrated in detail in post-buckling case.

Dynamic responses of functionally graded and layered composite beams

O. Kırlangıç,Ş.D. Akbaş 국제구조공학회 2021 Smart Structures and Systems, An International Jou Vol.27 No.1

This paper presents and compares the free and damped forced vibrations of layered and functionally graded composite beams. In the considered study, a cantilever beam subjected to a harmonic point load at the free end is investigated with layered and functionally graded materials. In the kinematics of the beam, the Timoshenko beam theory is used. The governing equations of problem are derived by using the Lagrange procedure. In the solution of the problem, the Ritz method is used. Algebraic polynomials are used with the trial functions for the Ritz method. In the obtaining of free vibration results, the eigenvalue procedure is implemented. In the solution of the damped forced vibration problem, the Newmark average acceleration method is used in the time history. In the damping effect, the Kelvin-Voigt viscoelastic model is used with the constitutive relations. In the numerical examples, the effects of material distribution parameter and dynamic parameters on the natural frequencies and forced vibration responses of functionally graded beams are obtained and compared with the results of the layered composite beam. Also, comparison studies are performed in order to validate the used formulations.

기공이 포함된 경사기능재료의 탄성계수 산출 방법

이재철 사단법인 한국융합기술연구학회 2023 아시아태평양융합연구교류논문지 Vol.9 No.8

A functionally graded material (FGM) is a two-component composite with a gradient transition from one component to the other. FGMs are typically fabricated with pressureless sintering of powdered metals, because it is relatively simple and inexpensive. However, this process inherently produces porous materials, as a result of solidification and crystallization. Additionally, the maximum sintering temperature is limited by the melting point of each component, which can lead to imperfect sintering and higher porosities. This porosity influences density and the mechanical properties of the final composite. Thus, it is important to be able to predict variations in the elastic modulus of FGMs including pores. While much research has been conducted on the mechanical effects of porosity in pure materials, analogous studies on composites are rare. The current study describes three models that predict elastic modulus as a function of FGM porosity. The first model uses the volume fraction of pores in each material of the composite while the second model assumes that porosity occurs only in the matrix material. The third model takes into account an empirical curve fit of the elastic moduli of pure materials as a function of porosity. Values calculated by each of the three proposed models were compared with those measured on Ni/Al2O3 FGMs. The third model showed the best agreement with the measured values FGM(Functionally Graded Material)은 한 구성 요소에서 다른 구성 요소로 그라데이션 전환이 있는 2개의 구성 요소로 이루어진 복합재이다. 분말 금속의 비가압 소결로 제조된 FGM은 상대적으로 성형이 간단하고 저렴하다. 그러나 이 공정은 본질적으로 응고 및 결정화의 결과로 인해 기공을 생성한다. 또한 최대 소결 온도는 각 구성 요소의 녹는점에 의해 제한되어 불완전한 소결 및 더 높은 다공성을 보인다. 이 다공성은 최종 복합재의 밀도와 기계적 물성에 영향을 미친다. 따라서 기공을 포함한 FGM의 탄성계수 변화를 예측할 수 있는 것이 중요하다. 순수 재료에서 기공에 따른 기계적 물성 영향에 대한 많은 연구가 수행되었지만 복합 재료에 대한 유사한 연구는 거의 없다. 본 연구는 FGM 다공성의 함수로 탄성 계수를 예측하는 세 가지 모델을 제안한다. 첫 번째 모델은 복합 재료의 각 재료에서 기공의 부피 분율을 사용하는 반면, 두 번째 모델은 다공성이 매트릭스 재료에서만 발생한다고 가정하였다. 세 번째 모델은 다공성의 함수로서 순수 재료의 탄성 계수의 경험적 곡선 맞춤을 고려하였다. 세 가지 제안된 모델에 의해 각각 계산된 값은 Ni/Al2O3 FGM에서 측정된 값과 비교되었다. 그리고 세 번째 모델이 측정값과 가장 잘 일치하였다.

Incompatible Graded Finite Elements for Orthotropic Nonhomogeneous Media

Asmita Rokaya,Gokhan Egilmez,김정호 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.12

Orthotropic materials or composites are challenging to model due to different elastic properties in two in-plane directions, which requires sufficient mesh refinement to attain desired accuracy. In this regard, an accurate and efficient incompatible graded element is developed for modeling orthotropic functionally graded materials. Properties of Graded finite elements such as Young’s moduli (E11, E22), shear modulus (G12) and Poisson’s ratio (v12) vary. A new incompatible graded element is developed using user subroutines in Abaqus and are compared to available exact solutions. In this study, performance (QM6) graded element is compared with lower-order and higher-order compatible elements (Q4 and Q8) as well as linear triangular (T3) and quadratic triangular (T6) elements with aid of several numerical examples. Additionally, orthotropic graded plate with carbon fibers properties as well as a circular disc with orthotropic properties under internal pressure is included. Furthermore, a curved beam with radially graded properties under the bending moment is studied. Additionally, the performance of various graded elements is compared with analytical solutions using Russell error.

Non-linear longitudinal fracture in a functionally graded beam

Rizov, Victor I. Techno-Press 2018 Coupled systems mechanics Vol.7 No.4

Longitudinal fracture in a functionally graded beam configuration was studied analytically with taking into account the non-linear behavior of the material. A cantilever beam with two longitudinal cracks located symmetrically with respect to the centroid was analyzed. The material was functionally graded along the beam width as well as along the beam length. The fracture was studied in terms of the strain energy release rate. The influence of material gradient, crack location along the beam width, crack length and material non-linearity on the fracture behavior was investigated. It was shown that the analytical solution derived is very useful for parametric analyses of the non-linear longitudinal fracture behavior. It was found that by using appropriate material gradients in width and length directions of the beam, the strain energy release rate can be reduced significantly. Thus, the results obtained in the present paper may be applied for optimization of functionally graded beam structure with respect to the longitudinal fracture performance.

Thermal Characteristic Evaluation of Functionally Graded Composites for PSZ/Metal

Lim, Jae-Kyoo,Song, Jun-Hee The Korean Society of Mechanical Engineers 2000 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.14 No.3

The functionally graded material (FGM) is the new concept for a heat resisting material. FGM consists of ceramics on one side and metal on the other. A composition and microstructure of an intermediate layer change continuously from ceramics to metal at the micron level. This study is carried out to analyze the thermal shock characteristics of functionally graded PSZ/ metal composites. Heat-resistant property was evaluated by gas burner heating test using $C_2H_2/O_2$ combustion flame. The ceramic surface was heated with burner flame and the bottom surface cooled with water flow. Also, the composition profile and the thickness of the graded layer were varied to study the thermo mechanical response. Furthermore, this study carried out the thermal stress analysis to investigate the thermal characteristics by the finite element method. Acoustic emission (AE) monitoring was performed to detect the microfracture process in a thermal shock test.

경사기능재료를 사용한 스마트 무인기 덕트의 열해석과 크리프 해석

임종빈(Jong-Bin Im),윤동영(Dong-Young Yoon),이정진(Jung-Jin Lee),박정선(Jung-Sun Park) 한국항공우주학회 2006 韓國航空宇宙學會誌 Vol.34 No.1

무인항공기는 엔진에서 연료의 연소, 배기관에서 고온의 연소 배기 가스등으로 인하여 많은 부분에 고온이 발생한다. 이는 전체 구조물의 안정성에 심각한 영향을 미칠 수 있는 사항이다. 경사기능재료는 고온의 환경에서 열에 저항하기 위해 한쪽 재료는 세라믹으로, 다른 쪽 재료는 가볍고 구조적 강성을 지닌 금속재료로 점차적으로 변화된 재료를 사용한 일종의 복합재료이다. 경사기능재료는 뛰어난 내열성을 가지는 특성으로 고온 상태에서 많이 사용된다. 이에 따라 본 논문에서는 경사기능재료를 무인항공기의 엔진 배기 덕트에 적용하여 열적 거동을 고찰하였고, 경사기능 충이 20개, 40개, 60개, 80개, 100개인 경사기능재료를 덕트 구조물에 적용하여 각각의 열 및 열응력 해석을 수행하여 비교 분석하였다. 또한, 경사기능재료를 사용한 고온 내열 배기 덕트의 크리프 해석을 수행하여 그 특성에 대해 고찰하였다. The high temperature occurs due to the combustion gas from engine in unmanned aerial vehicles (UAV). The high temperature may cause serious damages in UAV structure. The Functionally Graded Material (FGM) is chosen as a candidate material of the engine duct structure. A functionally graded material (FGM) is a two-component mixture composed by compositional gradient materials from one material to the other. In contrast, traditional composite materials are homogeneous mixtures, and involve compositions between the desirable properties of the component materials. Since significant proportions of an FGM contain the pure form of each material, the need for compromise is eliminated. The properties of both components can be fully utilized. Thermal stress analysis of FGM layers (20, 40, 60, 80 and 100) is performed in this paper. In addition, the creep behavior of FGM applied in duct structure of an engine is analyzed for better understanding of FGM characteristics.