Quasi-static Mechanical Tests Research Articles

Constitutive Model of Epoxy Resin Filled by Nano-Rubber Particles

In the MTS testing machine, Quasi-static tensile mechanical testing is carried on to different Nano rubber epoxy, and have gained its mechanical properties; basing on the testing figures, ZWT constitutive model is used to descript the tensile mechanical properties of materials, and five parameter values are gained under low frequency of the model through numerical fitting; With the comparison of the test data , the numerical fitting result is in good agreement with test, at the same time, it also show that ZWT constitutive model can well descript the Quasi-static tensile mechanical properties of epoxy resin filled by nano-rubber.

Validation of vibration testing for the assessment of the mechanical properties of human lumbar motion segments

Experimental modal analysis is a non-destructive measurement technique, which applies low forces and small deformations to assess the integrity of a structure. It is therefore a promising method to study the mechanical properties of the spine in vivo. Previously, modal parameters successfully revealed artificially induced spinal injuries. The question remains however, whether experimental modal analysis can be applied successfully in human spinal segments with mechanical changes due to physiological processes. Since quasi-static mechanical testing is considered the “gold standard” for assessing intervertebral stiffness, the purpose of our study was to examine if the mechanical properties derived from vibration testing and quasi-static testing correlate.Six cadaver human spines (L1–L5) were loaded quasi-statically in bending and torsion, while an optical system measured the angular rotations of the individual motion segments. Subsequently, the polysegmental spines were divided into L2–L3 and L4–L5 segments and a shaker was used to vibrate the upper vertebra, while its response was obtained from accelerometers in anteroposterior and mediolateral directions. From the resulting frequency response function the eigenfrequencies (ratio between stiffness and mass) and vibration modes (pattern of motion) were determined.The vibration results showed clear eigenfrequencies for flexion–extension (mean 121.83Hz, SD 40.05Hz), lateroflexion (mean 132.17, SD 34.80Hz) and axial rotation (mean 236.17Hz, SD 81.45Hz). Furthermore, the correlation between static and dynamic tests was significant (r=0.73, p=0.01). In conclusion, the findings from this study show that experimental modal analysis is a valid method to assess the mechanical properties of human lumbar motion segments.

Biodegradable single-polymer composites from polyvinyl alcohol

The microstructure and thermomechanical behaviour of a novel fully biodegradable polyvinyl alcohol (PVOH)-based single-polymer composite (SPC) is presented. Three kinds of PVOH stapled fibres, having different melting temperatures and tensile mechanical properties, were considered as a reinforcement, whilst plasticized PVOH granules were selected as a continuous matrix. Calorimetric tests on the constituents showed significantly different melting temperatures between the matrix and the fibres, thus evidencing adequate processing windows for the preparation of SPCs. On the other hand, scanning electron microscopy on the cryofractured surfaces of melt-mixed and compression-moulded SPCs experimentally proved that the morphological integrity of the reinforcement was maintained only when high melting temperature fibres were utilized. Quasi-static mechanical tensile tests highlighted the capability of the selected PVOH fibres to remarkably increase the elastic modulus, the stress at yield and the Vicat softening temperature of the PVOH matrix. Moreover, dynamic storage modulus and glass transition temperature of SPC increased with respect to the neat PVOH over the whole range of considered temperatures, whilst short-term creep stability was strongly improved, proportionally to the fibre content. The application of a time–temperature superposition principle to creep data confirmed the effectiveness of these fibres in increasing the long-term creep stability of the resulting materials.

Mechanical properties of single bovine trabeculae are unaffected by strain rate

For a better understanding of traumatic bone fractures, knowledge of the mechanical behavior of bone at high strain rates is required. Importantly, it needs to be clarified how quasistatic mechanical testing experiments relate to real bone fracture. This merits investigating the mechanical behavior of bone with an increase in strain rate. Various studies examined how cortical and trabecular bone behave at varying strain rates, but no one has yet looked at this question using individual trabeculae. In this study, three-point bending tests were carried out on bovine single trabeculae excised from a proximal femur to test the trabecular material's strain rate sensitivity. An experimental setup was designed, capable of measuring local strains at the surface of such small specimens, using digital image correlation. Microdamage was detected using the bone whitening effect. Samples were tested through two orders of magnitude, at strain rates varying between 0.01 and 3.39s−1. No linear relationship was observed between the strain rate and the Young's modulus (1.13–16.46GPa), the amount of microdamage, the maximum tensile strain at failure (14.22–61.65%) and at microdamage initiation (1.95–12.29%). The results obtained in this study conflict with previous studies reporting various trends for macroscopic cortical and trabecular bone samples with an increase in strain rate. This discrepancy might be explained by the bone type, the small sample geometry, the limited range of strain rates tested here, the type of loading and the method of microdamage detection. Based on the results of this study, the strain rate can be ignored when modeling trabecular bone.

Mechanical Behavior of Alpha, Beta, and Gamma Plutonium

Plutonium is a highly unusual metal displaying six allotropic phases between room temperature and 550 Centigrade. The crystal structures present vary from low-density high-symmetry cubic phases to high-density low-symmetry monoclinic phases, presenting unique challenges and opportunities for the researcher. In addition, the properties of plutonium may change over time due to radioactive decay, introducing radiation damage and causing changes in chemistry.Castings of high-density Plutonium were created as part of a research and development effort at Los Alamos National Laboratory. The as-cast material was characterized using a variety of techniques, including resonant ultrasound spectroscopy (RUS), dilatometry, and quasi-static mechanical testing. A brief overview of the experimental technique of RUS as it applies to plutonium will be presented, along with discussion of the elastic moduli of alpha plutonium measured in the newly as-cast state. Compression tests of alpha plutonium and tensile tests of beta and gamma phase plutonium will be presented and compared with previous literature and experiments including older alpha plutonium specimens by previous authors.

Constitutive Property Behavior of Type N and Type S Mortars

Abstract An extensive program of quasi-static mechanical property tests was conducted to characterize the mechanical behavior of type N and type S mortars under various stress and strain boundary conditions to decide which mortar to use in the construction of triple-brick and brick-over-block walls. The material characterization effort consisted of hydrostatic compression, unconfined compression, triaxial compression, direct pull, reduced triaxial extension, and uniaxial strain tests. The results from all of the quasi-static tests provided the mechanical properties required for determining which mortar to use in the construction of target walls for projectile perforation experiments as well as the constitutive model coefficients for numerical simulations of these experiments. This paper provides a summary of the mechanical property test results obtained for type N and type S mortars and the rational for using type S mortar in the construction of triple-brick and brick-over-block walls.

Microstructure and mechanical properties of differently extruded AZ31 magnesium alloy

Abstract Profiles of the magnesium alloy AZ31 were produced by conventional indirect extrusion and by indirect extrusion into counterpressure with variations of the billet temperature TB from 200 °C up to 350 °C. Microstructural examination by optical microscopy showed that for extrusion trials carried out with billet temperatures TB ≤ 250 °C fine dynamically recrystallized grains are found while elongated grains of the former cast structure remain. Above TB ≥ 300 °C most grains show higher dynamic recrystallization kinetics and additional static recrystallization and increase to grain sizes of d = 30 – 50 μm. At TB ≤ 250 °C the typical extrusion fiber texture is found, at TB ≥ 300 °C a double fiber texture is formed due to static recrystallization. The results of the quasistatic mechanical tests are due to these differences in the microstructure.

Mechanical and dynamic viscoelastic properties of hydroxyapatite reinforced poly(ε-caprolactone)

Poly(ε-caprolactone)/hydroxyapatite (PCL/HA) composites as potential bone substitutes were prepared by melt-blending. The melting, crystallization and glass transition temperatures deduced from differential scanning calorimetery and dynamic mechanical thermal analysis (DMTA) were all changed by the addition of HA, suggesting an interaction at the interface of these two phases. Quasi-static mechanical testing shows that the yield strength and Young's modulus of PCL were increased by the addition of the reinforcement filler, HA. Dynamic viscoelastic properties were investigated using DMTA and an advanced rheometric expansion system. The results show that both the storage modulus and viscous modulus are enhanced by HA, and the PCL composite melts still behave like pseudo-plastic liquid.

Contact stresses in the knee joint in deep flexion

The contact stresses in the knee that arise from activities involving deep flexion have not been given due consideration in view of social and cultural practice amongst many Asians that frequently cause the engagement of these activities. Excessively large stresses (>25 MPa) can cause cartilage damage and may be the precursor to the development of degenerative disease of the joint. In this study, forces in the knee derived from previous studies of human walking and squatting were applied to five cadaver knees that underwent quasi-static mechanical testing. This was conducted using a materials-testing machine and a custom-made apparatus that allowed secure and consistent loading of the knee specimen in flexion beyond 120°. A thin-film electronic pressure transducer was inserted into the cadaver tibiofemoral joint space to measure force and area. Throughout the various positions simulating specific phases of walking, it was found that stresses peaked to 14 MPa (standard deviation was 2.5 MPa). In deep flexion, the peak stresses were significantly larger by over 80%, reaching the damage limits of cartilage. The results from this biomechanical study suggest that the adequacy of articular cartilage to support loads in the knee joint during deep flexion may be questionable.

Development of a new peel-stopper for sandwich structures

A device referred to as a peel-stopper with the purpose of eliminating the risk of catastrophic skin debonding in sandwich structures in general, and high-speed ships in particular, has been developed. Two major advantages of the new peel-stopper are its simplicity of manufacture, and its lack of connections through the sandwich core. The latter is essential for good UNDEX performance. Two different versions were developed. Quasi-static mechanical tests were performed to verify the function of the peel-stopper, and the strength of the structure incorporating the peel-stopper. Regarding functionality, the peel-stoppers performed as expected. Regarding quasi-static strength, it was shown that the peel-stoppers could be made such that no structural strength reduction occurs.

Dynamic mechanical testing of the creep and relaxation properties of polyvinylidene fluoride

The paper concerns material testing and characterizations of the time-dependent properties of polyvinylidene fluoride (PVDF), a thin film piezoelectric polymer. The study is based on the assumptions of linear viscoelastic theory of hereditary type and time-temperature equivalence principle. A developed experimental program involves quasi-static creep tests and dynamic mechanical tests. The results of this study validate the assumptions of linear viscoelasticity in application to PVDF thin films and provide consistent empirical database regarding the creep and relaxation properties of PVDF in the material directions parallel and perpendicular to the orientation of the aligned molecular chains of the polymer.

Effects of loading rate on strength of the proximal femur

Results from previous quasi-static mechanical tests indicate that femurs from elderly subjects fail in vitro at forces 50% below those available in a fall from standing height. However, bone is a rate-dependent material, and it is not known whether this imbalance is present at rates of loading which occur in a fall. Based on recent data on time to peak force and body positions at impact during simulated falls, we designed a high rate test of the femur in a loading configuration meant to represent a fall on the hip. We used elderly (mean age 73.5 +/- 7.4 (SD) years) and younger adult (32.7 +/- 12.8 years) cadaveric femurs to investigate whether (1) the strength, stiffness, and energy absorption capacity of the femur increases under high rate loading conditions; (2) elderly femurs have reduced strength, stiffness, and energy absorption capacity compared with younger adult femurs at this loading rate; and (3) densitometric and geometric measures taken at the hip correlate with the measured fracture loads. Femurs were scanned using dual-energy X-ray absorptiometry (DXA) and then tested to failure in a fall loading configuration at a displacement rate of 100 mm/second. The fracture load in elderly and younger adult femurs increased by about 20% with a 50-fold increase in displacement rate. However, energy absorption did not increase with displacement rate because of a twofold increase in stiffness at the higher loading rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Anisotropy in the dynamic non-linear viscoelastic properties of bovine compact bone

A non-linear model is proposed to characterize the mechanical behaviour of compact bone and has been validated by mechanical tests on bovine femoral compact bone. The model consists of a non-linear spring and a non-linear dashpot in parallel. The method of identifying the viscoelastic parameters in the model is discussed. Impact and quasi-static compressive mechanical tests have shown that the model can be applied to bone to represent its mechanical behaviour at strain rates up to 100 s-1. The directional dependence of the viscoelastic parameters for the bone are determined and discussed.