Force-displacement characteristics of simply supported beam laminated with shape memory alloys

As a preliminary step in the nonlinear design of shape memory alloy（SMA） composite structures,the force-displacement characteristics of the SMA layer are studied.The bilinear hysteretic model is adopted to describe the constitutive relationship of SMA material.Under the assumption that there is no point of SMA layer finishing martensitic phase transformation during the loading and unloading process,the generalized restoring force generated by SMA layer is deduced for the case that the simply supported beam vibrates in its first mode.The generalized force is expressed as piecewise-nonlinear hysteretic function of the beam transverse displacement.Furthermore the energy dissipated by SMA layer during one period is obtained by integration,then its dependencies are discussed on the vibration amplitude and the SMA＇s strain（Ms-Strain） value at the beginning of martensitic phase transformation.It is shown that SMA＇s energy dissipating capacity is proportional to the stiffness difference of bilinear model and nonlinearly dependent on Ms-Strain.The increasing rate of the dissipating capacity gradually reduces with the amplitude increasing.The condition corresponding to the maximum dissipating capacity is deduced for given value of the vibration amplitude.The obtained results are helpful for designing beams laminated with shape memory alloys.

Parameter Identification Based on Force-Displacement Curves for a Bolted Joint Finite Element Model

In order to identify the uncertain parameters of a bolted joint finite element model,a simple and applicable way of parameter identification is introduced.By utilizing numerical simulation with the Abaqus software and experimental investigation with the MTS material testing system,the tangential force-displacement curves that reflect the characteristics of the bolted joint were acquired.On the basis of this,by employing the response surface methodology（RSM）and genetic algorithms（GAs）,parameters in the FEM model were identified.The force-displacement curves by both virtual and experimental approaches are well correlated at the end.This phenomenon-based parameter identification method may help facilitate precise prediction of complex jointed connection structures.

Mechanical Characterization of the Soft Tissues of a Native Human Knee： A Pilot Study

The importance of ligaments in providing joint stability and the incidence of injuries, dictates a need to increase their structural and mechanical properties understanding. Additionally, one of the challenges in the orthopedic industry is to design TKA （total knee arthroplasty） aiming to be soft-tissues friendly. This requires a priori knowledge of physiological knee function, in which the passive stability is achieved and guaranteed by the complex envelope of soft tissues around the joint. Therefore, the knowledge of the mechanical behavior of knee ligaments is fundamental. For this reason, our study aims to define and apply in a pilot study, an ad-hoc methodology to mechanically characterize ligaments of native human knees. The cruciate and collateral ligaments from a fresh frozen cadaver leg were accurately harvested. Each ligament was independently tested during a tensile test at different strain rates, simulating different deformation speeds during gait. Moreover, additional tensile tests until failure were also performed. Axial force and deformation were continuously recorded during each test. Results show that each ligament exhibited own typical non-linear, speed-related behavior. High repeatability in the results is observed among the different repeated tests confirming the robustness of the used methodology. This information will be helpful for clinicians, engineers and researchers to improve the biomechanical knowledge about knee, to develop better implants and to be able to improve the currently available numerical models of the human knee.

Study on microscale adhesion between solid surfaces with scanning probe

The adhesion between two parallel solid surfaces is of great interest with the rapid development of micro-nano devices and instruments.The adhesion forces between a flat tip with a diameter^1.7μm and some surface have been determined by recording the force-displacement curves with an atomic force microscope(AFM).The flat tip is used to prevent wear and mimic the adhesion between two parallel surfaces.The free energy of the solid surface is calculated by the contact angles between the probe liquids and the surface.The adhesion force between parallel solid surfaces cannot be predicted by the theory of thermodynamic surface free energy.The adhesion measurements were carried out under ambient conditions,in a nitrogen-filled glove box,under distilled water,and under potassium chloride(KCl)solution.The outcome shows that the real contact area without the applied load is only a small proportion of the apparent contact area.The measurement stability and repeatability of adhesion by the AFM depend on the surface characterization,measurement methods and the environment.Under different environments,there are different interactions and factors affecting the adhesion force,and the dominant interactions and factors may be different too.The various interactions and factors are mutually coupled to determine the final adhesion force.

Effect of electroacupuncture on muscle state and infrared thermogram changes in patients with acute lumbar muscle sprain

OBJECTIVE:To observe the effect of electroacupuncture(EA) on force-displacement value(FDV)of muscle state and the temperature index of infrared thermogram in patients with acute lumbar muscle sprain.METHODS:Patients with acute lumbar muscle sprain were randomly divided into a medication group and an EA group.The medication group(n-60) were treated with diclofenac sodium dual release enteric-coated capsules,75 mg per day for 7days.The EA group(n = 60) received EA at bilateral Houxi(SI 3),Jiaji(EX-B2),and Ashi points,at 20-30 mm depth and 10-25 Hz frequency for 20 min daily for 7 days.Muscle states were determined by measuring FDVs of the bilateral lumbar muscle with a Myotonometer fast muscle state detector.The temperature index of the lumbar skin was measured before and after treatment with a Fluke Ti30 non-refrigerated focal plane infrared thermal imaging detector.RESULTS:There were no significant pre-treatment differences between the medication group and the EA group in mean FDV(P = 0.052) or temperature index of the lumbar skin(P = 0.25).The cure rate was 63.3%in the EA group and 53.3%in the medication group.The total efficacy in the EA group(93.3%) was not significantly different from that in the medication group(86.6%,P = 0.204).After treatment,the mean FDV of the lumbar muscle significantly increased in both groups(P < 0.05 for both groups);the FDV increase in the EA group was significantly higher than in the medication group(P = 0.015).The temperature index was also significantly increased in both groups(P < 0.05 for both groups);the infrared thermogram in the EA group indicated significantly greater recovery compared to the medication group(P = 0.026).CONCLUSION:Both EA and diclofenac sodium markedly improved acute lumbar sprain,but EA better improved the rehabilitation and regeneration of FDVs and temperature index of infrared thermogram of the muscle.

Probing interactions at two-dimensional heterointerfaces by boron nitride-wrapped tip

Non-covalent interactions are important for two-dimensional heterointerfaces but challenged to be accurately determined,especially when the dielectric hexagonal boron nitride(BN)is involved.Here,we present a comprehensive quantitative investigation on the interactions at the interfaces of BN-BN,BN-molybdenum disulfide,and BN-graphite using a BN-wrapped atomic force microscope tip and first-principle theory.The critical adhesion forces at BN-molybdenum disulfide and BN-graphite interfaces are measured to be 1.107±0.062 and 0.999±0.053 times that at BN-BN interface,respectively,while increase to 1.195±0.076 and 1.085±0.075 a.u.after exposure of the tip to radiation in scanning electron microscopy,with data repeatability higher than 86%.The result with non-radiated tip agrees with the van der Waals interactions predicted by the state-of-the-art density functional theory-based vdW2D method,whereas the effect of radiation comes from the introduced charges in the tip,indicating the crucial roles of both dispersion and electrostatic interactions in construction,manipulation and device application of two-dimensional heterostructures.

Tensile behaviors of filaments with misfit of chirality

Slender chiral filaments are ubiquitous in both artificial and biological materials.Due to their chiral microstructures,chiral filaments usually exhibit favorable properties such as superior elasticity and unusual stretch-twist coupling deformation.However,how these chiral microstructures affect the elastic behavior of filaments remains unclear.In this paper,a refined Cosserat rod model with misfit or mismatching of chirality induced by inhomogeneous arrangement of chiral microstructures incorporated is developed.Using the refined rod model,the force-displacement relationships and variation of structural chirality during the tensile processes of two typical helical structures,i.e.,single-strand helix and double-strand helix,are investigated.The results show that the misfit of chirality can lead to a bend-twist deformation with a high coupling degree,which makes the rod much“soft”when stretched.The chiral filaments undergo an unusual twist when stretched,corresponding to an obviously nonlinear variation of structural chirality.The work suggests that the misfit of chirality can be used to tune the elastic behavior of chiral filaments,which is helpful in guiding the design of flexible actuators and soft devices.