• Composites Research
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• v.27 no.3
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• pp.90-95
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• 2014

Cure shrinkage during cure process of polymer matrix composites develope residual stress that cause some structural deformation, such as spring-in, spring-out and warpage. The carbon/epoxy prepreg used in this study is Hexply M21EV/34%/UD268NFS/IMA-12K supplied by Hexcel corp. Cure shrinkage and degree of cure measured by TMA(thermomechanical analyzer) and DSC(differential scanning calorimetry). Cure shrinkages are measured by TMA within a temperature range of $140{\sim}240^{\circ}C$ in a nitrogen atmosphere, and degree of cure determined by the heat of reaction using dynamic and isothermal DSC runs in argon atmosphere. As a result, the cure shrinkage is increased dramatically in a degree of cure range between 27~80%. the higher the cure temperature, the lower the degree of cure occurring to begin cure shrinkage.

• Steel and Composite Structures
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• v.19 no.1
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• pp.93-110
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• 2015

The thermomechanical bending response of anti-symmetric cross-ply composite plates is investigated by the use of the simple four variable sinusoidal plate theory. The theory accounts for sinusoidal distribution of transverse shear stress, and satisfies the free transverse shear stress conditions on the top and bottom surfaces of the plate without using shear correction factor. By dividing the transverse displacement into bending and shear parts, the number of unknowns and governing equations for the present theory is reduced, significantly facilitating engineering analysis. The validity of the present theory is demonstrated by comparison with solutions available in the literature. Numerical results are presented to demonstrate the behavior of the system. The influences of aspect ratio, side-to-thickness ratio, thermal expansion coefficients ratio and stacking sequence on the thermally induced response are studied. The present study is relevant to aerospace, chemical process and nuclear engineering structures which may be subjected to intense thermal loads.

• Nuclear Engineering and Technology
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• v.31 no.3
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• pp.267-275
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• 1999

This paper deals with the industrial problem of thermal striping damage on the French prototype fast breeder reactor, Phenix and it was studied in coordination with the research program of IAEA. The thermomechanical and fracture mechanics evaluation procedure of thermal striping damage on the tee-junction of the secondary piping using Green's function method and standard FEM is presented. The thermohydraulic(T/H) loading condition used in the present analysis is the random type thermal loads computed by T/H analysis on the turbulent mixing of the two flows with different temperatures. The thermomechanical fatigue damage was evaluated according to ASME code section 111 subsection NH. The results of the fatigue analysis showed that fatigue failure would occur at the welded joint within 90,000 hours of operation. The assessment for the fracture behavior of the welded joint showed that the crack would be initiated at an early stage in the operation. It took 42,698.9 hours for the crack to propagate up to 5 mm along the thickness direction. After then, however, the instability analysis, using tearing modulus, showed that the crack would be arrested, which was in agreement with the actual observation of the crack. An efficient analysis procedure using Green's function approach for the crack propagation problem under random type load was proposed in this study. The analysis results showed good agreement with those of the practical observations.

• Advances in concrete construction
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• v.11 no.1
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• pp.11-18
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• 2021

The present study fabricated polyvinyl alcohol (PVA) fiber-reinforced alkali-activated slag/fly ash (AASF) composites with varying mixture ratios of slag and fly ash. The thermomechanical behaviors of the AASF composites exposed to 200, 400, 600, or 800℃ were evaluated by means of compressive strength test, visual observation, and fire resistance tests. X-ray diffractometry, mercury intrusion porosimetry, and thermogravimetry tests were performed to analyze the microstructure change of the AASF composites upon exposure to high temperatures. Specimens exhibited a gradual strength loss up to 600℃, while also showing a significant decrease in the strength above 600℃. The fire resistance test revealed the occurrence of an inflection point as indicated by an increase in the internal temperature at around 200℃. In addition, specimens showed the dehydration of C-S-H gel, the presence of åkermanite, gehlenite, and anorthite upon exposure to 800℃, which is associated with the formation of macropore population with pores having diameters of 1-3 ㎛ and 20-40 ㎛. Visual observation indicated that the PVA fibers mitigated the cracking and/or spalling of the specimens upon exposure to 800℃.

• Advances in aircraft and spacecraft science
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• v.7 no.6
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• pp.475-493
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• 2020

This paper is focused on the characterization of the thermomechanical properties of semicrystalline poly-ether-ether-ketone (PEKK) and of carbon fiberreinforced thermoplastic based laminated composites (C/PEKK) below and above the glass transition temperature (T_g). Differential Scanning Calorimetry (DSC), Dynamic Mechanical Analysis (DMA) and tensile tests are carried out on both pure PEKK polymer and [(±45)₂, +45]_s C/PEKK composite samples, showing a significant similarity in behavior. The employment of a simple micromechanical model confirms that the mechanical and physical behavior of the polymer and that of the matrix in the composite are similar.

• Journal of Welding and Joining
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• v.25 no.3
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• pp.37-44
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• 2007

Mechanical and thermomechanical properties of the bulk metallic glass (BMG) are so unique that the deformation behavior is largely dependent on the temperature and the strain rate. Impacting behavior of NiTiZrSiSn bulk metallic glass powder during kinetic spraying was investigated in this study. Considering the impact behavior of the BMG, the kinetic spraying system was modified and attached the powder preheating system to make the transition from the inhomogeneous deformation to the homogeneous deformation of impacting BMG particle easy BMG splat formation is considered from the viewpoint of the adiabatic shear instability. It is suggested that the impact behavior of bulk metallic glass particle is determined by the competition between fracture and deformation. The bonding of the impacting NiTiZrSiSn bulk amorphous particle was primarily caused by the temperature-dependent deformation and fracture (local liquid formation) behavior.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.6 s.165
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• pp.1001-1010
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• 1999

Thermo-mechanical behavior of discontinuous shape memory alloy(SMA) reinforced polymeric composite has been studied using modified shear lag theory and finite element(FE) analysis with 2-D multi-fiber model. The aligned and staggered models of short-fiber arrangement are employed. The effects of fiber overlap and aspect ratio on the thermomechanical responses such as the thermal expansion coefficient are investigated. It is found that the increase of both tensile stress(resistance stress) in SMA fiber and compressive stress in polymer matrix with increasing aspect ratio is the main cause of low thermal deformation of the composite.

• Journal of Powder Materials
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• v.5 no.2
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• pp.122-128
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• 1998

NiAl based ODS (Oxide Dispersion Strengthened) intermetallic alloys have been produced by mechanical alloying (MA) process and consolidated by hot extrusion. Subsequent thermomechanical treatments have been applied to induce secondary recrystallization in an attempt to improve creep resistance in this material. The creep behavior of secondary recrystallized MA NiAl has been investigated and compared with those of as-extruded condition. Minimum creep rate were shown to be approximately two orders of magnitude lower than that in as-extruded condition. The improvement in creep resistance is believed due to the grain coarsening, restricting of dispersoid coarsening as well as increase in grain aspect ratio. Creep threshold stress behavior, below which no measurable creep rate can be detected, has been discussed on the basis of particle-dislocation interaction theory. The threshold stress becomes negligible after secondary recrystallization in MA NiAl, presumably due to dispersoid coarsening and a decrease in grain boundary area during secondary recrystallization.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1302-1308
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• 2002

Thermo-mechanical and flexural behavior of a wire-bond plastic ball grid array (WB-PBGA) package are characterized by high sensitive moire interferometry. Moire fringe patterns are recorded and analyzed for several bending loads and temperatures. At the temperature higher than $100^{\circ}C$, the inelastic deformation in solder balls become more dominant, so that the bending of the molding compound decreases while temperature increases. The deformation caused by thermally induced bending is compared with that caused by mechanical bending. The strain results show that the solder ball located at the edge of the chip has largest shear strain by the thermal load while the maximum average shear strain by the bending moment occurs in the end solder.

• Transactions of the Korean Society of Mechanical Engineers
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• v.8 no.6
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• pp.599-603
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• 1984

Field equations describing the effective behavior of general heterogeneous media are derived from the integral balance relations through the methods of distribution and convolution.