Results Of Tension Tests Research Articles

Mechanical characterisation of polyurethane elastomer for biomedical applications

Mechanical testing and modelling of a material for biomedical applications have to be based on conditions representative of the application of interest. In this work, an ether-based polyurethane elastomer is used to build mock arteries. The aim is to study the behaviour of arteries under pulsatile loading conditions and how that behaviour changes with the development and progression of atherosclerosis. Polyurethane elastomers are widely used as biomaterials, e.g. in tube form for bypasses and catheters. However, their mechanical behaviour has not been extensively characterised. This work establishes the variations in the behaviour of polyurethane elastomer with temperature, humidity and strain rate and also reports planar and equibiaxial tension, relaxation, creep and cyclic test results, providing a comprehensive characterisation of the material. Test results are used to determine the properties of the polyurethane elastomer and in the selection of a representative material model for future simulations of arterial behaviour and the development of atherosclerosis. The results show that the behaviour of the elastomer is significantly dependent on both humidity and temperature, with Young’s modulus of 7.4 MPa, 5.3 MPa and 4.7 MPa under dry-room temperature, wet-room temperature and wet at 37 ∘C conditions, respectively. The elastomer also exhibits rate-dependent viscoelastic behaviour. Yeoh’s hyperelastic material model provided the best fit to the entire range of experimental data. The Neo-Hookean model provides a good fit at small strain but significantly diverges at large strains. Nevertheless, in applications where deformations are relatively small, i.e. below 15%, the Neo-Hookean model can be used.

DCB test simulation of stitched CFRP laminates using interlaminar tension test results

A simulation model for the delamination extension of stitched CFRP laminates and 3-D orthogonal interlocked fabric composites (3-D OIFC) has been developed using a 2-D finite element method incorporating interlaminar tension test results to simulate the experimental results of their DCB tests. The mechanical properties of through-the-thickness fiber were determined from the results of interlaminar tension tests in which the specimen included only one through-the-thickness yarn. The fracture phenomena around the through-the-thickness thread, such as debonding from the in-plane layer, slack absorption, fiber bridging, and the pull-out of broken threads from the in-plane layers, are also introduced into the FEM model. The present FEM simulation results were compared to DCB test results for certain stitched laminates and a 3-D OIFC, and the simulation results showed good agreement with the experimental results of DCB tests, including the load–displacement curve and Mode I strain energy release rate (GI). While it was difficult to estimate GI accurately when the DCB test specimen included different types of z-fiber fracture modes, the present model of FEM analysis can simulate the experimental results of DCB tests of stitched laminates and 3-D OIFC. It is suggested that the GI of CFRP with arbitrary z-fiber densities can be predicted by using this FEM analysis model together with interlaminar tension test results.

Limits of the linear viscoelastic behaviour of polyamide 66 filled with TiO 2 nanoparticles: Effect of strain rate, temperature, and moisture

Limits of linear viscoelastic behaviour of TiO 2 nanoparticle-filled polyamides are estimated quantitatively by the results of uniaxial tension tests. The stress limit of the filled polymer is higher than that of the un-filled one. Their values are the lower, the higher the temperature and moisture content of test specimens, and the lower, the lower the strain rate. The concept of an energy threshold for the linear viscoelastic behaviour is used to comprehensively characterize the limits over a wide range of test conditions. The energy limit is not affected by the strain rate, temperature, or moisture, and its value for the filled polymer is higher than that for the un-filled one. When plotted in the stress–strain axes, the data for different test conditions fall on a common curve described by a quasi-linear energy function. The higher the energy, the wider the region of the linear viscoelastic behaviour.

Mechanical characterization of single high-strength electrospun polyimide nanofibres

Ultimate tensile strength and axial tensile modulus of single high-strength electrospun polyimide [poly(p-phenylene biphenyltetracarboximide), BPDA/PPA] nanofibres have been characterized by introducing a novel micro tensile testing method. The polyimide nanofibres with diameters of around 300 nm were produced by annealing their precursor (polyamic acid) nanofibres that were fabricated by the electrospinning technique. Experimental results of the micro tension tests show that polyimide nanofibres had an average ultimate tensile strength of 1.7 ± 0.12 GPa, axial tensile modulus of 76 ± 12 GPa and ultimate strain of ∼3%. The ultimate tensile strength and axial tensile modulus of the electrospun polyimide nanofibres in this study are among the highest ones reported in the literature to date. The precursor nanofibres with similar diameters and molecular weights had an average ultimate tensile strength of 766 ± 41 MPa, axial tensile modulus of 13 ± 0.4 GPa and ultimate strain of ∼43%. The experimental stress–strain curves obtained in this study indicate that under axial tension, the precursor (polyamic acid) nanofibres behave as linearly strain-hardening ductile material without obvious softening at final failure, while the polyimide nanofibres behave simply as brittle material with very high tensile strength and axial tensile modulus. Furthermore, by using a transmission electron microscope, detailed fractographical analysis was performed to examine the tensile failure mechanisms of the polyimide nanofibres, which include chain scission, pull-out, chain bundle breakage, etc. X-ray diffraction analysis of the highly aligned polyimide nanofibres shows the high chain alignment along the nanofibre axis that was formed in the electrospinning process and responsible for the high tensile strength and axial tensile stiffness.

Formulation of a Viscoplasticity Model for Unidirectional Carbon Fiber-Reinforced Composites with Differences in Off-Axis Tensile and Compressive Behaviors

Formulation of a phenomenological viscoplasticity model that accounts for differences in tensile and compressive nonlinear rate-dependent behaviors of unidirectional carbon fiber-reinforced composites in a given off-axis direction is attempted. Effective stress and effective viscoplastic strain for transversely isotropic materials are derived from a three-dimensional pressure-modified Hill's anisotropic yield criterion, and they are reduced to the forms for plane state of stress. A plane-stress viscoplasticity model furnished with a capability to predict the phenomena raised above is formulated on the basis of the concept of overstress and the irreversible thermodynamics with internal variables. A shear constraint parameter, in which the influence of the compressive transverse stress on the shear flow resistance is reflected, is taken into account in defining a modified form of effective viscoplastic strain rate to enhance the predictive capability of the viscoplasticity model. The viscoplasticity model discussed in the present study is designed so as to be reduced to the viscoplasticity model of the Gates-Sun type developed in the previous study, which allows easy identification of material constants. Validity of the proposed viscoplasticity model is evaluated by comparing with results of off-axis tension and compression tests on a unidirectional carbon/epoxy composite at different strain rates.

Plasticity Characteristics of Beta Titanium Alloy Obtained Using Depth-Sensing Nano-Indentation Test

In this study, depth sensing nano-indentation test was carried out to investigate the plastic/viscoplastic behavior of beta titanium alloy. The indentation experiment results showed that both hardening and softening effect existed in indentation process and the residual penetration depth was deeper when the nominal indentation strain rate increased. That is opposite to the room temperature tension test results, which showed a strain rate hardening behavior. FEM simulation combined with viscoplastic model was carried out to simulate the indentation procedure. FEM results showed that the pile-up pattern changed with the consideration of the nominal indentation strain rate effect. Atom force microscope (AFM) observation gave a same result of pile-up patterns.

High purity nanolatex prepared by ultrasonically irradiated emulsion polymerization

Ultrasonically initiated emulsion copolymerization of styrene and a cationic polymerizable surfactant (methacryloxyethyl dodecydimethyl ammonium bromide, C12N+) was successfully employed to prepare high purity copolymer nanolatex. C12N+ can play the roles of an emulsifier, an initiator, and a comonomer at the same time. It has an excellent initiation efficiency and reactivity. The rate of copolymerization was high and styrene conversion achieved 95% in an hour. Nanoscale latex particles with average diameter 40nm were obtained easily under ultrasonic irradiation. Results of FTIR, 1H NMR and surface tension tests proved almost all surfmers had copolymerized with styrene when the C12N+ concentration was more than 0.030g/mL, indicating high purity nanolatex without residual emulsifiers was obtained.

Experimental investigation of interlaminar mechanical properties on carbon fiber stitched CFRP laminates

Experimental investigations of interlaminar mechanical properties for carbon fiber rein-forced plastic (CFRP) laminates were carried out using aramid fiber (Kevlar®-29 1000d) and carbon fiber (TR40-1K 612d, Mitsubishi Rayon) stitching. Various carbon fiber (CF) stitch densities were used to prepare a number of CF stitched CFRP laminates for double cantilever beam (DCB) tests. An insert tongue-type loading fixture, developed by the Japan Aerospace Exploration Agency (formerly the National Aerospace Laboratory of Japan), was also employed in the DCB test. Interlaminar tension tests were carried out under an out-of-plane directional loading using a single CF stitch thread in the CFRP laminates. The DCB test results clarified that the relationship between the volume fractions of the CF stitch thread (V ft) and mode I critical energy release rate (G Ic) showed a mostly linear function with a higher gradient than that of the Kevlar® stitched CFRP laminates. The CF stitched CFRP tension test results indicated that the consumption energy per unit area (Ei ) was larger than that of Kevlar® stitched CFRP laminates.

부착특성을 고려한 철근콘크리트 부재의 휨 균열폭 산정 및 비교

In recent years, the availability of high-strength reinforcing and prestressing steels leads us to build economically and efficiently designed concrete structural members. One of critical problems faced to the structural engineers dealing with these types of structural member is controls of crack width that is used as a criterion for the serviceability in the limit state design. Especially, flexural cracking must be controlled to secure the structural safety and to improve the durability as well as serviceability of the load carving members. The proposed method utilizes the results of pure tension test in which tensile loads are applied both side of specimen, done by Ikki. The bond characteristics of deformed reinforcing bar under pure tension is considered by the area of concrete and rib area. The results of proposed method are compared with the test data and the results show that the proposed method can take into account the dimensions, variation of sectional properties, and direction of reinforcing and gives more accurate maximum bond stress and corresponding relative slip than the existing methods. the characteristics of bonding is considered by using dimensionless slip magnitude and effective reinforcement ratio. The validity of the proposed equation is verified by test experimental data.

Semisolid Roll Casting of Aluminum Alloy Strip and Its Properties

A356 was cast into the strip by the semisolid strip casting using an unequal diameter twin roll caster. This process was one of the rheocasting. The semisolid slurry was made by a cooling slope. Solid fraction was about 5%. The casting speed was 20 m/min, and the thickness was 4.4 mm. The as-cast strip could be cold rolled down to 1 mm. The result of tension test of 1mm-thickness-T4 heat-treated strip was as below. Tensile stress was 223 MPa, 0.2 proof stress was 123 MPa and elongation was 21.8%. Deep drawing could be operated to 1 mm-thickness T4 sheet, and L.D.R was attained to 2.0. In some condition, 180 degrees bending could be operated without crack at outer surface. These results mean that semisolid roll cast A356 strip may be able to use for press forming.

Bake Hardening of Hot Rolled Multiphase Steels under Biaxial Pre‐strained Conditions

Multiphase steels show a strong bake hardening effect being of importance for shaping of car body structural parts. The raised yield strength is exploited for improved crash resistance. Especially the automotive industry has a growing interest in using this effect. Normally the bake hardening effect is examined in tensile tests whereas under industrial conditions shaping of structural parts shows a wide spread of stress strain behaviour, from uniaxial conditions over plain strain to biaxial ones. So it is obvious that the bake hardening behaviour of a material cannot be described with results of the uniaxial tension test only. To give a first answer to this question, the dependence of the bake hardening effect on different biaxial prestrains was investigated for several hot rolled multiphase steels using various baking temperatures and holding times whereas the bake hardening effect under uniaxial prestrain had already been examined in [5]. Considering the choices to generate biaxial strain, a Marciniak forming tool with a diameter of 250 mm mounted on a 2500 kN hydraulic press was chosen. For control of plastic deformation and adjustment the non‐contact measuring system ARGUS, was used. To reduce the quantity of experiments “Design of Experiments” and statistical methods were applied for a martensitic steel, a dual phase steel, a complex phase steel, a ferrite‐bainite steel, and a retained austenite steel known as TRIP, all in hot rolled condition. As a result, a formula for yield stress, tensile strength and residual deformability was developed. Furthermore, a method was found to predict easily whether a steel under investigation is qualified for additional experiments in regard to bake hardening or more exactly its response to different baking temperatures and holding times.

Simple constitutive model for nonlinear response of fiber-reinforced composites with loading-directional dependence

Polymeric composites generally exhibit different nonlinear response in tension and compression tests. In this study, Sun and Chen’s one-parameter plasticity model [Sun C.T. and Chen J.L., 1989. A simple flow rule for characterizing nonlinear behavior of fiber composites, J Compos Mater 29, 457–463] is extended to incorporate the loading-directional dependence on the plastic flow in composite laminates. Off-axis specimens of unidirectional carbon/epoxy composites were tested in compression and tension. Based on experimental results of compression tests, a simple two-parameter constitutive model for characterizing nonlinear mechanical behavior of fiber-reinforced composites was established. Finally, comparison of model predictions with experimental results of off-axis tension tests indicated a good correlation between the two. The developed simple plasticity model can explain the difference of nonlinear response in tension and compression tests.

Fatigue and residual stress relaxation of deep rolled differently aged aluminium alloy AA6110

The precipitation-hardened aluminium wrought alloy AA6110 (Al–Mg–Si–Cu) was heat treated to the ageing conditions under-, peak- and over-aged. Deep rolling was applied at room temperature for all ageing conditions. Residual stresses and work hardening states near the surface of the deep rolled condition were characterized by X-ray diffraction methods. Depth profiles of residual stresses, full width at half maximum (FWHM) values of the X-ray diffraction peaks and microhardness near the surface of the deep rolled non-, under-, peak- and over-aged conditions are presented. Results of quasistatic tension tests of non-surface treated specimens are given to characterize the heat treatment state. The cyclic deformation behavior, s/n-curves and residual stress relaxation during fatigue tests have been investigated by stress-controlled fatigue tests at room temperature. Several polished and deep rolled non-aged (as-quenched) specimens were fatigued as a reference. The effect of deep rolling on fatigue lifetime as compared to polished specimens is discussed.

Two-Parameter Parabolic Mohr Strength Criterion and Its Damage Regularity

A series of formulas about two-parameter parabolic Mohr strength criterion(2-PP Mohr criterion) are derived. Based on the results of uniaxial tension and uniaxial compression tests, the parameters involved in the criterion can be easily determined, then the criterion in terms of the major principal stress and the minor principal stress is derived, and the damage pattern is also discussed. At last, the formulas about the rupture angle and the friction angle are presented, and their relationship is also given. 2-PP Mohr criterion can describe not only shear but also tensile failure. In this criterion the ratio of the uniaxial compression strength and the uniaxial tension strength is not confined as in Griffith criterion. The formula about the rupture angle provides steady theoretical foundation for determining the direction of crack faces and damage patterns in the computation of macro crack propagation. In fact, Griffith criterion is only a special case of the two-parameter parabolic Mohr strength criterion proposed in this present paper.

Mechanical Properties of Fine-Grained AA1050 after ECAP

The mechanical properties of fine-grained Aluminium AA1050 produced by ECAP at room temperature, have been investigated under various deformation modes. Because ECAP leads to an unstable microstructure, some samples were annealed at 300°C for 10 minutes in order to stabilise the microstructure. For mechanical testing, cylindrical samples were used in three types of monotonic deformation tests: axisymmetric compression, uniaxial tension and simple shear by torsion. The influence of the deformation mode on the yield locus and strain hardening behaviour has been studied and will be discussed for both hot rolled AA1050, ECAP samples without annealing and annealed ECAP samples. To achieve a better understanding of the strain hardening, some preliminary tests with a change in strain path were also performed. The results of tension tests followed by compression will be reported.

액체로켓 연소기 재생냉각 챔버 구조설계

재생냉각형 액체로켓 연소기의 냉각채널 설계에 대한 탄-소성 구조설계를 수행하였다. 구조해석에 필요한 데이터를 얻기 위하여 여러 가지 온도에서 재생냉각 챔버 제작에 사용하는 구리합금의 단축인장시험을 수행하였다. 재료시험 결과 구리합금은 브레이징 공정 후에 연화되어 강도 값이 매우 저하되며 온도가 증가함에 따라 유동 응력 값이 더 작게 나타났다. 재료시험 데이터를 이용하여 냉각채널의 구조해석을 수행한 결과 채널 내부 냉각유체에 의한 내부압력보다 고온의 연소가스에 의한 열 하중에 의하여 채널의 변형이 심하게 발생함을 확인하였다. 따라서 기계적인 하중을 견딜 수 있는 한도 내에서 냉각채널의 두께를 감소시켜 열 하중을 최소화함으로서 연소기의 무게 감소, 냉각성능 향상, 그리고 구조적인 안정성을 향상시킬 수 있다는 것을 알 수 있었다. Elastic-plastic structural analysis for regenerative cooling chamber of liquid rocket thrust chamber is performed. Uniaxial tension test is also conducted for the copper alloy in order to get material data necessary for the structure analysis. The results of uniaxial tension test reveal that copper alloy become ductile after brazing process and flow stress becomes lower as temperature becomes higher. As a result of structural analysis using the material data, the deformation of cooling channel is more increased by thermal load than by internal pressure of cooling fluid. Therefore, the results of analysis show that structural stability and cooling performance of combustion thrust chamber which is designed to endure mechanical load and minimized a channel thickness are improved by decreased thermal load as possible.

A Novel Planar Tension Test of Rubber for Evaluating the Prediction Ability of the Modified Eight-Chain Model under Moderate Finite Deformation

Abstract In this paper, a novel planar tension test is applied to evaluate the prediction ability of the rubber constitutive models under moderate finite deformation. Based on the automated grid method, it is found that in planar test, deformation in the center region of the specimen is homogeneous but that of the whole specimen is heterogeneous. With three dimensional (3D) finite element (FE) modeling, both the load-stretch relationship and the deformation fields predicted by various constitutive models are obtained under heterogeneous deformation state of the planar tension. By comparing FEA results to the test results, the prediction abilities of these constitutive models are evaluated. According to the results of this heterogeneous planar tension test, the modified eight-chain model is found to be more successful than the eight-chain model and the Van del Waals model in predicting the observed hyperelastic behaviors of rubber material under different deformation states.

Residual Stress Relaxation and Cyclic Deformation Behavior of Deep Rolled AlMg4.5Mn (AA5083) at Elevated Temperatures

The cyclic deformation behavior of deep rolled and polished aluminium wrought alloy AlMg4,5Mn in the temperature range 20-300°C has been investigated. Results of quasistatic tension and compression tests of untreated specimens in the temperature range 20-300°C are presented. To characterize the fatigue behavior for stress-controlled tests as a function of test temperature, s-n curves, cyclic deformations curves and mean strains as a function of number of cycles are given. The residual stress- and work hardening states near the surface of deep rolled aluminium alloy AlMg4.5Mn before and after fatigue tests were investigated by X-ray diffraction methods. The investigated AlMn4.5Mn aluminium alloy shows cyclic hardening until fracture at all stress amplitudes in stress-controlled fatigue tests at 25-150°C. With increasing temperature the deformation behavior shifts from cyclic hardening to cyclic softening. Below a certain stress amplitude at a given temperature deep rolling led to a reduction of the plastic strain amplitude as compared to the untreated state through cyclically stable near-surface work hardening as indicated by stable FWHM-values. This reduction in plastic strain amplitude is associated with enhanced fatigue lives. The effectiveness of deep rolling is governed by the cyclic and thermal stability of nearsurface work hardening rather than macroscopic compressive residual stresses. Since nearsurface work hardening is known to retard crack initiation, deep rolling is also effective in temperature- and stress ranges where macroscopic compressive residual stresses have relaxed almost completely, but where near-surface work hardening prevails. Above certain stress amplitudes and temperatures, deep rolling has no beneficial effect on the fatigue behavior of AlMg4.5Mn. This is a consequence of instable near-surface microstructures, especially instable near-surface work hardening.

Fatigue of deep rolled AlMg4.5Mn (AA5083) in the temperature range 20–300°C

Abstract The cyclic deformation behavior of deep rolled and polished aluminium wrought alloy AlMg4.5Mn has been investigated in the temperature range from 20 to 300 °C. Results of quasistatic tension and compression tests of untreated specimens are presented. To characterize the fatigue behavior for stress-controlled tests as a function of test temperature, stress-life-curves, cyclic deformations curves and mean strains as a function of number of cycles are given. Residual stresses and work hardening effects near the surface of the deep rolled condition before and after fatigue tests were investigated by X-ray diffraction methods.

Edge machining effects on the failure of polymer matrix composite coupons

This papers deals with the influence of the machining procedure of carbon/epoxy and glass/epoxy composite coupons on their mechanical performances. First, a literature review is presented to summarize the rather small number of studies dedicated to this subject. Then, machining procedures are detailed and evaluated by surface roughness measurements and microscopic observations. Finally, results of Iosipescu shear tests and ring tension tests are reported and discussed. The main conclusion of this study is that there is a significant effect of machining procedure on composite coupons strength for certain sets of parameters but that surface information (roughness, microscopic observation) is not enough to explain them. Further work is necessary on this subject to derive relevant machining quality criteria with a view to mechanical performance.