The Effect of Thin Film Adhesives on Mode I Interlaminar Fracture Toughness in Carbon Fiber Composites with Shape Memory Alloy Inserts

Shape Memory Alloy (SMA) was placed within Polymer Matrix Composite (PMC) panels alongside film adhesives to examine bonding. Double cantilever beam (DCB) testing was performed using ASTM D5528. C-scanning was performed before testing, modal acoustic emissions (MAE) were monitored during testing, and microscopy performed post-test. Data was analyzed using modified beam theory (MBT), compliance calibration (CC) and modified compliance calibration (MCC) methods. Fracture toughness for control specimens was higher than previously reported due to fiber-bridging. Specimens with SMAs and adhesives stabilized crack propagation. Results revealed SMA-bridging; a phenomenon mimicking fiber-bridging which increased the load and fracture toughness of SMA specimens

Effect of Thin-Film Adhesives on Mode I Interlaminar Fracture Toughness in Carbon Fiber Composites with Shape Memory Alloy Inserts

A single sheet of NiTi shape memory alloy (SMA) was introduced within a unidirectional HexPly 8552/IM7 (Hexcel) polymer matrix composite (PMC) panel in conjunction with multiple thin-film adhesives to promote the interfacial bond strength between the SMA and PMC. A double cantilever beam (DCB) test was performed in accordance with the ASTM D5528 method for evaluation of Mode I interlaminar fracture toughness of unidirectional fiber-reinforced PMCs. The modal acoustic emissions (MAEs) were monitored during testing with two acoustic sensors attached to the specimens. The composite panels were subjected to a C-scan before testing and examined using optical and scanning electron microscopy (SEM) techniques after part failure. The data were used in conjunction with modified beam theory (MBT), the compliance calibration (CC) method, and the modified compliance calibration (MCC) method. The Mode I interlaminar toughness (G(sub IC)) values for control specimens were higher than previously reported and are attributed to extensive fiber bridging during testing. The presence of adhesives with SMA inserts stabilized crack propagation during DCB testing. The results reveal a new phenomenon of SMA bridging, whereby crack propagation would switch from one side of the SMA insert to the other, thus increasing the load and G(sub IC) values of specimens containing SMA

Influence of Silicon Carbide Particulates on Tensile Fracture Behavior of an Aluminum Alloy

In this research paper the tensile properties and fracture characteristics of an Al–Cu–Mg alloy discontinuously reinforced with silicon carbide particulates (SiCp) are presented and discussed. The increased strength of the Al–Cu–Mg/SiCp composite is attributed to the synergistic influences of residual stresses arising from intrinsic differences in response of the composite constituents, that is, metal matrix and ceramic-particle reinforcements, during cyclic deformation and strengthening from constrained plastic flow and triaxiality in the ductile aluminum alloy metal matrix due to the presence of ceramic particle reinforcements. Fracture on a microscopic scale comprised of cracking of both the individual silicon carbide particulates and even the clusters of silicon carbide particles present in the microstructure. Final fracture of the composite resulted from crack propagation through the matrix between the clusters of reinforcing SiC particles. The key mechanisms governing the tensile fracture process are discussed

The Tensile Response and Fracture Behavior of Four High Strength Specialty Steels

In this technical paper the role of alloy chemistry and secondary processing on tensile response and final fracture behavior of four high strength steels is presented and discussed. The conjoint influence of composition, secondary processing and intrinsic microstructural features in governing stress versus strain response and tensile properties is highlighted. The macroscopic mode and intrinsic microscopic features that result from final fracture of the four high strength steels is discussed. The intrinsic microscopic mechanisms governing tensile deformation and final fracture behavior of the high strength steels are outlined in light of the specific role played by composition, intrinsic microstructural effects and nature of loading

Influence of Surface Finish and Notch on Flexural Strength and Fracture of a High-Performance Alloy Steel for Innovative Applications

In this article, the extrinsic influence of surface finish and notch on flexural strength and fracture behavior of the alloy steel, Pyrowear 53, when subjected to quasi-static bending is presented and discussed. The influence of surface finish on bevel-shaped samples of Pyrowear 53 revealed the isotropic surface finish to carry a higher maximum load during a flexural test. However, from the standpoint of extension, the micromachine-processed samples revealed observable improvement in extension (mm) capability when subjected to static bending. Samples of this alloy steel having a funnel notch had a lower maximum-load-carrying capability when compared one-on-one with the bevel-shaped sample. The macroscopic fracture mode and the microscopic features on the fracture surface are presented and discussed in light of shape of the test specimen. The key microscopic mechanisms governing fracture behavior of this novel steel are discussed in light of the role played by intrinsic microstructural features, deformation characteristics of the microstructural constituents and nature of loading

Synthesis and Characterization of Ultrafine Tungsten Samples Produced by Plasma-Activated Sintering

Plasma-activated sintering was used to densify micron-size tungsten powders to obtain bulk samples. This sintering technique offers the capability of producing bulk samples having a very high density. The average size of the starting tungsten powder particles was 4·61 µm. Using a combination of pressure and temperature, during sintering, 11 different samples were prepared. The bulk samples were produced over a range of pressure from 41 to 61 MPa. At selected pressure levels of 47–61 MPa, the bulk samples produced were sintered at different temperatures. Microstructural observations and density measurements provide evidence for the presence of porosity at both the microscopic and macroscopic levels. The extrinsic influence of processing parameters used during sintering, namely, pressure and temperature, on microstructural development to include the presence, size and distribution of porosity, density, microhardness, nanohardness and stiffness is presented and discussed

The Quasi-Static and Cyclic Fatigue Fracture Behavior of an Emerging Titanium Alloy

Sustained research and development efforts culminating in the emergence of new and improved titanium alloys have provided both the impetus and interest for studying their mechanical behavior under the extrinsic influence of loading spanning both static and dynamic. In this article, the quasi-static and cyclic fatigue fracture behavior of a titanium alloy (Ti-Al-V-Fe-O2) is highlighted. Test specimens of this titanium alloy were deformed both in quasi-static tension and cyclic stress amplitude–controlled fatigue. The quasi-static mechanical properties, cyclic fatigue response and microscopic mechanisms contributing to deformation and eventual fracture are highlighted in light of the competing and mutually interactive influences of nature of loading, intrinsic microstructural effects, deformation characteristics of the titanium alloy metal matrix and macroscopic aspects of fracture

The Bearing Strength and Fracture Behavior of Bolted Connections in Two Aluminum Alloys

In this paper, the bearing capacity, taken as a combination of strength, elongation, and failure by fracture characteristics of bolt holes in two aluminum alloys, 5052-H32 and 6061-T6, that were deformed in uniaxial tension is presented and discussed. The specific role played by bolt hole confinement on the bearing capacity of each aluminum alloy is highlighted. An increase in the bearing ratio caused plastic deformation around the holes to gradually increase. For both the chosen aluminum alloys the average bearing ratio at the time of failure of the test sample was found to vary with end distance. The experimentally determined strength was observably larger than the calculated bearing strength obtained using guaranteed minimum mechanical properties and recommended mathematical relationships. The nature of final fracture of each aluminum alloy is carefully examined and the intrinsic features present on the fracture surface are rationalized in concurrence with macroscopic mechanical response

The Quasi-Static Deformation and Fracture Behavior of Novel High-Strength Steel for Emerging Applications

In this study, the quasi-static deformation and final fracture behavior of Pyrowear 53 is presented and discussed. This novel alloy steel has noticeably improved strength-, ductility- and fatigue-related properties to offer than other competing high-strength alloy steels having near similar chemical composition and processing history. The conjoint influence of composition and secondary processing on intrinsic microstructural effects, stress versus strain response, tensile properties and final fracture behavior are highlighted. The macroscopic fracture mode and microscopic features on the tensile fracture surface are presented and discussed in light of test specimen orientation. The intrinsic microscopic mechanisms governing tensile deformation and final fracture behavior of this novel steel are discussed in light of the role played by intrinsic microstructural features, deformation characteristics of the microstructural constituents and nature of loading

Infuence of Welding and Heat Treatment on Microstructure, Properties and Fracture Behaviour of a Wrought Aluminium Alloy

Welding of aluminium alloy, belonging to the 6XXX series, exerts an adverse influence on its strength. The loss of strength immediately adjacent to the welds can have an influence on overall behaviour of the structure or component. In this study, the technique of gas metal arc welding was used. The filler material used was a silicon-containing aluminium alloy. Subsequent to welding, the alloy (6061-T4) was subjected to post-weld heat treatment (PWHT) at 185°C for 6 h. Both the as-welded and artificially aged extrusions of aluminium alloy 6061 were examined for both microstructural development and resultant influence on mechanical properties. Light optical microscopy was used to characterise the microstructure of the starting material. The PWHT had a marginal influence on both the presence and distribution of second-phase particles in the microstructure. The temperature and time of heat treatment should result in the precipitation and presence of very fine precipitate particles in the microstructure. Tensile tests revealed the welded aluminium alloy to have lower strength, both yield strength and ultimate tensile strength, when compared to the as-provided un-welded counterpart. The influence of PWHT on strength, ductility and fracture properties of the alloy, in comparison with the as-provided material, is presented and discussed