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The mechanical properties of jujube flesh were investigated by using ramp-hold tests to obtain the stress-time and strain-time relation of jujube fresh under compress load. Furthermore, CCD camera was used to measure the deformation of specimen during the tests. Linear viscoelastic constitutive models were used to describe the time dependent mechanical behavior of jujube flesh. The instantaneous and long-term elastic moduli of jujube fresh were obtained from the stress and strain relations at the beginning and end of ramp-hold tests. The relaxation coefficients of linear viscoelastic model were computed by using least square fitting procedure with fixed characteristic times. The results show that a linear viscoelastic model with three relaxation time constants can well describe the time dependent force behaviour of jujube fresh under unconfined compression. However, linear viscoelastic model cannot describe the lateral deformation of specimen under compression.

In the joint replacement surgery, the alumina ceramic are widely used as femoral heads for total hip replacements as an alternative to metal parts. Alumina ceramic materials has good mechanical properties, corrosion resistance, wear resistance, and biocompatible properties. However, the alumina ceramics typically exhibit brittle behavior thus limiting their performance under certain conditions. Due to some machining difficulties, there is almost no direct measurement of dynamic tensile properties of ceramics in the strain rate ranges between 500 s−1 and 5000 s−1. To understand dynamic tensile response of alumina ceramics, Flattened Brazilian Disc method with Split Hokinson Pressure Bar was utilized. In this research, the dynamic fracture process of the alumina ceramic at various tensile loading rates was studied. The effects of sample size were also monitored and analyzed. This paper explores the feasibility of applying the tensile behavior of alumina ceramics to total hip arthroplasty using a Brazilian Disc method.

Tendrils of some species of plants freely coil between their bases and tips to drag up the shoot and ensure no waste of shoot growth. In this study, the drag force generated by tendrils of the luffa plant (Luffa cylindrica) during free coiling was evaluated using a force measurement system that consisted of cantilever wire apparatus, CCD camera and finite element analysis software. How the stiffness of an object to which is attached the tip of tendrils affects the development of drag force because of free coiling was investigated. Experimental results showed that the tendril attached to a stiffer support could take longer to develop drag force and generate stronger drag force than one attached to a less stiff support. The drag force developed by free coiling of the luffa tendril could be on the order of 0.17 N. This force is sufficient to pull up more than eight times the internodal weight of the luffa shoot without other support. The relation between the magnitude of drag force generated by free coiling and the contraction ratio of the tendril was elucidated. The drag force–time curves show that the rate of increase in drag force resulting from free coiling of luffa tendrils in the first 20 h is higher than that after 20 h.

In this study, the mechanical properties of Caladium (Caladium × hortulanun Birdsey) petiole were investigated. The petiole was considered as a composite beam which consists of rind and core parts. To classify the mechanical properties of rind and core part of petioles, two-phase three-point bending tests were conducted on the specimens cut from petioles. Linear beam theory was used to convert the time-dependent bending forces, during the three-point bending tests, to relaxation moduli. The result shows that the mechanical properties of rind and core parts of Caladium are very different. The relaxation modulus of rind is approximate 40 times higher than relaxation modulus of core at time = 600 s after applying bending load, and the relaxation time distribution of core is wider than the relaxation time distribution of core. The three- and seven-parameter linear viscoelastic constitutive models were used to describe the time-dependent relaxation moduli of rind and core of caladium petiole. The fitted results show that the seven-parameter Wiechert model can describe the viscoelastic behaviour of Caladium petiole very well. The finite element analysis was used to assess the error of this test methodology. The reaction force error because of the tapered diameter of specimens is about 12%.

Due to the advance in digital image acquisition systems, optical methods for measurement have become more and more popular. The Moire effect is a well-known method which can be used to measure in-plane and out-of-plane deformations. Fourier transform moire method and grid method (FTMGM) is an excellent method for full-field, large in-plane deformation measurement, and can be implemented for the in-plane strain measurement of polymeric materials. An easy and inexpensive method to prepare gratings on specimens for FTMGM is presented. In order to demonstrate this method, a cross grating was generated and was put onto a notched photoelastic plastic sheet. The subsequent fringe and strain analysis was carried out by a toolbox developed by the authors under the MATLAB environment.

In order to optimize the design of milling machinery for rice varieties, it is important to understand the mechanical properties such as strength and damage properties of grains of different varieties of rice. The ratio of amylose of rice not only affects the texture of cooked rice but also the mechanical properties of raw rice grain. In this study, the damage properties of different breeds of rice with three different levels of amylose ratios were investigated. The damage properties were investigated by using compression and three point bending tests. The compression tests were conducted on rice specimens with two parallel surfaces made from rice grains and the three point bending tests were conducted on whole rice grains. Although the compression force to break rice kernel under 3 point bending are similar for all types of rice under tests. It can be seen that, among the rice varieties under tests, Chainat 1, the high amylose ratio rice, has the highest compression strength. The understanding of this study can help the developing of methods and devices used for milling processing of rice with different level of amylose to reduce the milling losses.

In this study, the relations between the well-like sensory properties, crispness and firmness, of wax apple (Syzygium samarangense) and the texture properties were investigated by using double-bite tests. The strains of wax apples used in this study are Black Pearl and Tubtimchan. By comparing the sensory judgment and the TPA test results, the sensory judgment of crispness could be related to the TPA parameter fracturability. The wax apple with higher fracturability is considered to be crispier. However the sensory judgment of firmness cannot be direct correlated to any single TPA parameter. The sensory feeling of firmness could be related to the difference between hardness and fracturability.

This work investigated the time dependent mechanical properties of bovine enamel. The cubic specimens of enamel were prepared from bovine incisors and the ramp-hold compression tests were performed to acquire the stress-time and strain-time relation of enamel under compress load. In this study, enamel was considered as linear viscoelatic material. The long-term elastic modulus of enamel was evaluated from the stress and strain relations at the end of ramp-hold tests and the relaxation behaviour of enamel was estimated from the normalized stress-time curves of ramp-hold tests. The relaxation coefficients and characteristic times of linear viscoelastic model were obtained by using iterative inverse finite element method. The results show that a linear viscoelastic model with 3 relaxation time constants can well describe the time dependent behaviour of bovine enamel under uni-axial compression load.

This study examined the time dependent mechanical properties of porcine meniscus under unconfined compression condition. The ramp-hold compression tests with different ramping displacement rates and long-term compression tests with very low displacement rate were performed on porcine meniscus specimens. The time dependent mechanical response of porcine meniscus was described by hyper-viscoelastic constitutive model due to its simplicity and can be easily implemented to finite element models. Inverse iterative finite element analysis procedure was used to obtain the material parameters of hyper-viscoelastic models of meniscus in two stages. In the first stage, the long-term hyperelastic material parameters of meniscus were obtained from the compression test data with very low displacement rate. The long-term hyperelastic material parameters were used as known parameters in the second stage, and the time dependent material parameters were determined from the ramp-hold compression tests with different ramping displacement rates. It can be seen from the force-time curves of ramp-hold experimental data that the mechanical properties of meniscus is highly time-dependent. The instantaneous modulus is more than 50 times higher than the long-term elastic modulus. The third-order reduce polynomial hyper-viscoelastic model established in this study can well describe the mechanical behavior of porcine meniscus under compression load. This model can be used in the finite element study of meniscus biomechanics.

From a structural point of view, banana leaf is an outstanding design of biological system. This work used a procedure based on finite element analysis and inverse problem method to estimate elastic modui of different parts of banana petiole from compression test data. Two phase compression tests on petiole section specimens were performed to get the force-displacement data of petiole for inverse finite element analyses. The inverse analysis method was performed by using a MATLAB procedure to execute ABAQUS to obtain finite element results and read desirable data from finite element results for optimization procedure. The values of elastic moduli of skin and core of petiole estimated by current method are 28 MPa and 0.9 MPa respectively for the particular petiole section under test.

An inverse iterative finite element analysis procedure was developed to investigate mechanical properties of porcine articular cartilage under compression load. Specimen consists of articular cartilage and bone was cut from porcine femur for this study. The specimen was mounted on metal base plate and the compression tests were performed by using material test machine with flat compression plate. The ramp-hold compression tests with different ramping displacement rates and long-term compression test with very low displacement rate were performed on the specimens. The force and compression displacement as function of time were recorded. The profile of specimen was obtained from for generating the geometry model of specimen. The finite element model which consists of bone and cartilage parts was generated from the geometry model of specimen. In this study, bone and cartilage were considered as linear elastic material and hyperviscoelastic material respectively. The generalized pattern search method was used for the optimization process to find the long-term hyperelastic and viscoelastic parameters of cartilage by minimize the experimental loading forces and the reaction forces computed form finite element analysis. The results shows 2nd order reduce polynomial hyperelastic model with two viscoelastic time constants can well describe the mechanical response of articular cartilage and bone specimen under flat plate compression.

Tendril is a threadlike specialized stem, leaf or petiole used by climbing plants for support and attachment. The spiral contraction which occurs after a tendril has caught an object is of great use to the climbing plant. The spiral contraction can drags up the shoot thus there is no waste of growth. Besides, a far more important use rendered by the spiral contraction of the tendrils is that they are thus made highly elastic so that the force is distributed between several adjacent attached tendrils; and this renders the whole far stronger than it otherwise would be, as the tendrils cannot break separately. It is this elasticity that protects the plants from being torn away from their supports during stormy weather or pulled by object. In this study, the mechanical properties of Luffa tendrils were investigated. By using tensile experiments and finite element analyses, the time dependent mechanical properties of attached mature tendrils of Luffa under tensile loads were investigated. The improvement of supporting capability of Luffa tendrils due to spiral contraction was quantified. The results of the finite element analyses showed the maximum tensile force on a tendril can be reduced more than 58% due to distributing force to 4 adjacent attached tendrils when applied concentrated force on the stem.

In this study, the reconfiguration of Heliconia rostrata leaf was investigated by using fluid structure interaction (FSI) analysis at different wind speeds. In order to perform FSI analysis, the time dependent mechanical properties of petiole and lamina were modeled by using linear viscoelastic constitutive laws and the parameters were fitted from 3 point bending tests and tensile tests experimental data. Besides, in fluid domain, air is considered as incompressible fluid in this study. The drag force and banding moment of Heliconia rostrata leaf at different wind speeds (4 and 6 m/sec) under headwind condition were examined. The FSI analyses show that, compared with drag forces of rigid leaf under headwind, the drag forces of Heliconia rostrata leaf reduce 35% and 63% under 4 and 6 m/sec headwind conditions respectively. The findings of this study can help us design better flexible structures such as wind turbine blades.