Unidirectional Tensile Tests Research Articles

Bidirectional tensile testing cell for in situ small angle X-ray scattering investigations of soft tissue

An X-ray cell for the acquisition of one-dimensional mechanical force–displacement diagrams of soft tissue samples has been developed. The combination of X-ray and mechanical data allows new insights into the coupling of the macroscopic behavior and nanoscopic structural changes during the application of load. Two linear μ-translation stages are used to symmetrically – i.e. bidirectionally – stretch the sample. A video-extensometer is installed to record geometrical changes of the sample during measurement which allows to determine true stresses and strains. The sample can be immersed in a liquid and heated. We demonstrate the advantages over common unidirectional tensile testing devices without length measurement systems by comparing different mechanical and diffraction data sets of human arterial tissue.

Fatigue behaviour of oil palm fruit bunch fibre/epoxy and carbon fibre/epoxy composites

Unidirectional tensile tests were carried out on oil palm fruit bunch fibre (OPFBF)/epoxy composite and carbon fibre (CF)/epoxy composite to determine their modulus and ultimate tensile stress (UTS). The UTS determined from these tests were then used as the fatigue test parameters. Two different values of fibre volume ratios, V f, namely 35% and 55% were studied for OPFBF/epoxy composite. Fatigue tests using constant stress amplitude were carried out for OPFBF/epoxy and CF/epoxy composites at the stress ratios of 0.1 and 0.5 and frequency of 20 Hz. The results for tensile properties and fatigue behaviour as well as failure mechanism were evaluated. The results show that the UTS values for OPFBF is 24.9 MPa and for OPFBF/epoxy composite with 35% fibre volume ratio is 47.78 MPa.

Experimental Characterization of an Integrated Sandwich Composite Using 3D Woven Fabrics as the Core Material

In this article, an integrated sandwich composite adopting 3D woven fabrics as the core material was experimentally characterized for its effective elastic modulus as well as its capacity of receiving impact energy. Featured by its porous core for leak detection and high strength to weight ratio, the integrated sandwich composite was an ideal candidate to be fabricated into a large part to store volatile chemical liquids or gas. To characterize the integrated sandwich composite for such applications, a series of unidirectional tensile tests as well as impact experiments were conducted for the sandwich composite fabricated using two different types of reinforced lamina as the face-sheets.

Characterization of the Effective Elastic Modulus of an Integrated Sandwich Composite

In this paper, an integrated sandwich composite adopting 3-D woven fabrics as the core material is thoroughly studied for its effective elastic modulus. In spite of the extensive applications of 3-D woven sandwich composites due to their improved mechanical properties, no suitable theoretical model has been proposed to predict the elastic modulus for such composite structures in the open literature so far. For the present work, a theoretical model by means of a micromechanics approach and the rule of mixtures is proposed to predict its effective in-plane elastic modulus. To verify the veracity of our prediction, unidirectional tensile tests were also carried out to determine the effective elastic modulus. Eventually, our experimental results turn out to agree with our prediction very well.

Elastic characterization of PEEK/IM7 using coefficients of thermal expansion

Abstract Three-dimensional elastic properties of a PEEK/IM7 unidirectional lamina are determined by an approach using laminate coefficient of thermal expansion (CTE) measurements and two known elastic constants. Specific relationships required to apply the technique and generate material elastic properties are derived from the general equations presented by the authors in a previous publication. The investigation emphasizes the feasibility and practical aspects of using CTE data to determine elastic properties. The room temperature elastic constants determined, based on measured CTEs, are compared with available data from the literature, obtained according to ASTM standard techniques. The approach, based on the CTE measurements, plus unidirectional tensile tests, allows the determination of all of the elastic constants, including the through-thickness Poisson's ratio ν23, which is not commonly quoted.

Multiple Cracking and Tensile Behavior for an Orthogonal 3‐D Woven Si‐Ti‐C‐O Fiber/Si‐Ti‐C‐O Matrix Composite

This paper presents experimental results for the multiple microcracking and tensile behavior of an orthogonal 3‐D woven Si‐Ti‐C‐O fiber (Tyranno™ Lox‐M)/Si‐Ti‐C‐O matrix composite with a nanoscale carbon fiber/matrix interphase and processed using a polymer impregnation and pyrolysis route. Based on microscopic observations and unidirectional tensile tests, it is revealed that the inelastic tensile stress/strain behavior is governed by matrix cracking in transverse (90°) fiber bundles between 65 and 180 MPa, matrix cracking in longitudinal (0°) fiber bundles between 180 and 300 MPa, and fiber fragmentation above 300 MPa. A methodology for estimation of unidirectional tensile behavior in orthogonal 3‐D composites has been established by the use and modification of existing theory. A good correlation was obtained between the predicted and measured composite strain using this procedure.

Room temperature creep behavior of nanocrystalline nickel produced by an electrodeposition technique

Deformation processes of nanocrystalline (6–40 nm) nickel produced by an electrodeposition technique were studied. First, the results of unidirectional tensile tests were discussed with respect to the deviation from the Hall-Petch relationship. It was suggested that such a mechanical behavior exhibited by nanocrystalline materials could be described by a composite model proposed previously. Further experimental work on static and dynamic creep tests under the load control condition showed that nanocrystalline nickel electrodeposits exhibited a significant room temperature creep behavior. It appeared that grain boundary sliding and diffusive matter transport within the intercrystalline region played an important role in terms of deformation mechanisms of nanocrystalline materials. The contributions of dynamic creep to stress-strain behavior and, in turn, to the assessment of the Hall-Petch relationship for nanocrystalline materials are discussed.

Characterization of the Fiber-Matrix Interphase and its Influence on Mechanical Properties of Unidirectional Composites

The fiber-matrix interphase is commonly altered in graphite fiber rein-forced composites by changing the level of surface treatment imparted to the fibers and by using different fiber sizings. In this study, the influence of both surface treatment and fiber sizing on the mechanical properties of unidirectional composites was studied. Three material systems having the same high modulus Apollo carbon fibers (manufactured by Courtoulds Research) and HC 9106-3 toughened epoxy matrix, but with different fiber sizing and surface treatment, were used to study the effects of the interphase. For convenience, these are designated 810 A, 820 A and 8100 systems. The fibers used in the 810 A and 8100 systems received 100% industry standard surface treatment, while the fibers used in the 820 A system received 200% industry standard surface treatment. The "A" and "O" represent unreacted bisphenol-A epoxy and polyvinylpyrrolidone (PVP) sizing respectively. The formation of distinctly different interphase in these three material systems was confirmed using a pernanganic etching technique. The etching study also revealed a highly nonuniform distribution of PVP in the 8100 system. Unidirectional tensile test results indicated significant reduction in the longitudinal stiffness of the PVP sized 8100 laminates. However, the tensile strength and failure strain of this system were vastly greater than those of the epoxy sized 810 A laminates. The systems with 10% and 200% levels of fiber surface treatment had similar longitudinal tensile properties. Transverse tensile test results indicated that the interracial bond strength was greatest in the 820 A system and lowest in the PVP sized 8100 system. The transverse flexural strength of the 8100 and 820 A systems were however found to be significantly greater than that of the 810 A system. It is postulated that the differences in unidirectional mechanical properties in these material systems are essentially due to differences in the interfacial bond strength and efficiency of load transfer from the matrix to the fiber.

The mechanical behaviour of PEEK short fibre composites

Short glass (GF) and carbon fibre (CF) reinforced poly-ether-ether-ketone (PEEK) composites were prepared by injection moulding and then microstructurally characterized. Their mechanical behaviour was determined by two different methods: a classical unidirectional tensile test and an immersion ultrasonic technique. The reinforcing effect of fibres is discussed in the context of the theory of reinforcement of Bowyer and Bader. Interfacial shear strength and critical fibre length at break are calculated for both PEEK/GF and PEEK/CF composites. Examinations of fracture surfaces of uniaxial tensile specimens revealed a higher adhesion of carbon fibres to PEEK matrix in regards to the adhesion concerning glass fibre-PEEK interfaces, which is in agreement with the results provided by the model. Compatibility of ultrasonic and tensile results is reported.

コーテッド平織物の観察と１軸伸張実験

Coated plain-weave fabrics are used as a membrane material of membrane structures including architectural membrane structures such as clear span air-supported membrane structure, flexible containers and airships. Uni/biaxial extension properties of coated fabrics are vary important for the design of membrane structures. In the present paper, the authors first presented SEM photographs of the surface and cut section to understand the structure of this material. Then unidirectional tensile tests were done up to failure. The stress-strain curves showed nonlineality and anisotropy. Some discussion was done on these properties. Poisson's ratio showed extreme nonlinearity at the stress region up to 20% of the failure stress which is the design stress. Specimens used here were a PTFE-coated grass fiber fabric and a PVC-coated polyester fabric which are widely used in the field of architectural membrane structure.

Investigation of the superplasticity of tin-lead eutectic by impression creep tests

The superplasticity of the Pb-Sn eutectic was investigated in the temperature range of 283 to 340 K. The strain-rate sensitivity, the activation energy and the activation volume were determined by impression creep measurements at various strain rates and temperatures. The results obtained are in good agreement with the results of conventional unidirectional tensile tests, which show that the simple and economic impression creep test can lead to equivalent results with the conventional creep test.

Size Effect on the Load-displacement Curves of Compact Specimen of SUS 316 Steel

The size effect on the crack growth in SUS 316 steel was studied by observations of load-displacement curves of many proportional compact specimens with various nominal widths. When the thickness was less than 0.2 times the width, the critical crack-tip opening-displacement (CTOD) for the start of steady crack growth was proportional to the thickness. The proportional constant was expressed by the experimental constants (yield stress, work-hardening parameters and fracture true stress) obtained by the unidirectional tensile tests. It was concluded that a ductile crack grows when the normal stress ahead of the crack-tip exceeds the fracture true stress of the materials.

Fatigue Characteristics of Open-End Thick-Walled Cylinders Under Cyclic Internal Pressure

Thick-walled cylinder fatigue data due to cyclic internal pressure for open-end cylinders in the range of 103 to 105 cycles to failure and having a diameter ratio of 1.4 to 2.0 at a nominal yield strength of 160,000 pounds per square inch is presented. Discussed and also presented are the effects of autofrettage on the fatigue characteristics of thick-walled cylinders. Autofrettage substantially enhances fatigue characteristics at stress levels below the corresponding overstrain pressure, the degree of improvement increasing the decreasing stress levels. The rate of improvement in fatigue characteristics increases significantly with diameter ratio in autofrettaged cylinders up to a diameter ratio of 1.8–2.0 and to a much smaller degree in the nonautofrettaged condition. The rate of improvement of fatigue characteristics above 2.0 is the same for both the autofrettaged and nonautofrettaged cases. It is shown that thermal treatment of 675 F for 6 hours after autofrettage does not affect fatigue characteristics and that there is a correlation between the cyclic-stress level and the area and depth of the fatigue crack to the point of ductile rupture. The depth of the fatigue crack decreases with increasing cyclic-stress level. A means for using data from a unidirectional tensile fatigue test to predict the fatigue characteristics of thick-walled cylinders is discussed.