PROPAGATION OF STRESS WAVE IN A FUNCTIONALLY GRADED NANO-BAR BASED ON MODIFIED COUPLE STRESS THEORY

In this paper, propagation of a one-dimensional elastic stress wave in a functionally graded (FG) nano-bar is analysed based on the modified couple stress theory. It is assumed that the material properties of FG bar are distributed as an exponential function along the axial direction. The two main advantages of the modified couple stress theory over the classical couple stress theory are the inclusion of a symmetric couple stress tensor and the involvement of only one material length scale parameter. According to the modified couple stress theory, only one material length scale parameter is used to describe the size effect in nano-bar. Also, the shear stress components come from the lateral inertia effect are considered in the elastic strain energy relation. Then, the governing equations are derived using Hamilton's principle and are generally solved. Finally, effects of length scale parameter, material inhomogeneity constant and Poisson's ratio on stress wave propagation velocity and harmonic behavior of stress wave are evaluated and can be observed that using the classical continuum theory leads to considerable errors in analysis of stress wave propagation

Investigation of flexibility constants for a multi-spring model: a solution for buckling of cracked micro/nanobeams

In this paper, a multi-spring model is used for modelling of the crack in a micro/nanobeam under axial compressive load based on a modified couple stress theory. This model includes an equivalent rotational spring to transmit the bending moment and an equivalent longitudinal spring to transmit the axial force through the cracked section, which leads to promotion of the modelling of discontinuities due to the presence of the crack. Moreover, this study considers coupled effects between the bending moment and axial force on the discontinuities at the cracked section. Therefore, four flexibility constants appear in the continuity conditions. In this paper, these four constants are obtained as a function of crack depth, separately. This modelling is employed to solve the buckling problem of cracked micro/nanobeams using a close-form method, Euler-Bernoulli theory and simply supported boundary conditions. Finally, the effects of flexibility constants, crack depth and crack location on the critical buckling load are studied

The role of tissue biomechanics in the implantation and performance of inflatable penile prostheses: current state of the art and future perspective

INTRODUCTION: Erectile dysfunction (ED) affects to some degree approximately 52% of the male population aged 40-70 years. Many men do not respond to, or are precluded from using, pharmaceutical treatments for ED and are therefore advised to consider penile prostheses. Different types of penile prosthesis are available, such as inflatable penile prostheses (IPPs). IPPs consist of a pair of inflatable cylinders inserted into the corpora cavernosa (CC). During inflation/deflation of these cylinders, the CC and other surrounding tissues such as the tunica albuginea (TA) are highly impacted. Therefore, it is critical to understand the mechanics of penile tissues for successful implantation of IPPs and to reduce tissue damage induced by IPPs. OBJECTIVES: We explored the importance of the biomechanics of penile tissues for successful IPP function and reviewed and summarized the most significant studies on penile biomechanics that have been reported to date. METHODS: We performed an extensive literature review of publications on penile biomechanics and IPP implantation. RESULTS: Indenters have been used to characterize the mechanical behavior of whole penile tissue; however, this technique applied only local deformation, which limited insights into individual tissue components. Although one reported study addressed the mechanical behavior of TA, this investigation did not consider anisotropy, and there is a notable absence of biomechanical studies on CC and CS. This lack of understanding of penile tissue biomechanics has resulted in computational models that use linear-elastic materials, despite soft tissues generally exhibiting hyperelastic behavior. Furthermore, available benchtop/synthetic models do not have tissue properties matched to those of the human penis, limiting the scope of these models for use as preclinical testbeds for IPP testing. CONCLUSION: Improved understanding of penile tissue biomechanics would assist the development of realistic benchtop/synthetic and computational models enabling the long-term performance of IPPs to be better assessed.Medical Instruments & Bio-Inspired Technolog

The role of tissue biomechanics in the implantation and performance of inflatable penile prostheses: current state of the art and future perspective

Introduction: Erectile dysfunction (ED) affects to some degree approximately 52% of the male population aged 40-70 years. Many men do not respond to, or are precluded from using, pharmaceutical treatments for ED and are therefore advised to consider penile prostheses. Different types of penile prosthesis are available, such as inflatable penile prostheses (IPPs). IPPs consist of a pair of inflatable cylinders inserted into the corpora cavernosa (CC). During inflation/deflation of these cylinders, the CC and other surrounding tissues such as the tunica albuginea (TA) are highly impacted. Therefore, it is critical to understand the mechanics of penile tissues for successful implantation of IPPs and to reduce tissue damage induced by IPPs. Objectives: We explored the importance of the biomechanics of penile tissues for successful IPP function and reviewed and summarized the most significant studies on penile biomechanics that have been reported to date. Methods: We performed an extensive literature review of publications on penile biomechanics and IPP implantation. Results: Indenters have been used to characterize the mechanical behavior of whole penile tissue; however, this technique applied only local deformation, which limited insights into individual tissue components. Although one reported study addressed the mechanical behavior of TA, this investigation did not consider anisotropy, and there is a notable absence of biomechanical studies on CC and CS. This lack of understanding of penile tissue biomechanics has resulted in computational models that use linear-elastic materials, despite soft tissues generally exhibiting hyperelastic behavior. Furthermore, available benchtop/synthetic models do not have tissue properties matched to those of the human penis, limiting the scope of these models for use as preclinical testbeds for IPP testing. Conclusion: Improved understanding of penile tissue biomechanics would assist the development of realistic benchtop/synthetic and computational models enabling the long-term performance of IPPs to be better assessed.</p