Biaxial testing of textile material - methodology and instrument assembly procedure

Membrane structures are becoming popular because of the potential usage in structures with higher aesthetic claims. For the roofing of these structures, different textile materials are used. These special materials offer an alternative to conventional roofing materials and allow, besides its lightweightness, also a possibility to roof a difficult floor plan and big span. When designing such a construction, there are some challenges related to the properties of the specific material. In order to exploit the full potential of textile membrane materials, it is necessary to choose an appropriate material model for numerical modelling, which takes into account its nonlinear behaviour. The two most important material characteristics needed for characterizing the behaviour are Young’s modulus of elasticity and Poisson’s ratio. Since the material is orthotropic in most cases, it is necessary to test the material in two directions; therefore, these characteristics need to be obtained from the biaxial test. This contribution is focused on the research of the methodology of biaxial tests and test instrument assembly procedure, which will be used for the following testing of textile materials.

Development Of A Biaxial Testing Apparatus

<div>Material testing is a crucial part of engineering design and development, especially in aerospace engineering as it is more cost effective to test an element or component than doing a full-scale test on the completed part. Typically, uniaxial testing is carried out to characterize a material,</div><div>which is adequate for finding the properties of the material. However, these kinds of tests are inadequate for simulating the real-world loading that a component may experience in its life cycle. Therefore, this project’s goal was to develop a low-cost biaxial testing apparatus using off-the-shelf components, including the Arduino Uno microcontroller (“Arduino”), stepper motors (“motors”), and load cell. This report outlines the development of the software required to</div><div>operate the motors and read output value of the load cell. The Arduino code used to control the motors was developed using open-source code available on GitHub and the Stepper library, which contains the required functions for controlling the motors. The Arduino code can be used</div><div>to determine the strain rate of up to 11 𝑚𝑚/𝑚𝑖𝑛, as well as the type of loading (tension or compression) along each axis. </div>

Development Of A Biaxial Testing Apparatus

<div>Material testing is a crucial part of engineering design and development, especially in aerospace engineering as it is more cost effective to test an element or component than doing a full-scale test on the completed part. Typically, uniaxial testing is carried out to characterize a material,</div><div>which is adequate for finding the properties of the material. However, these kinds of tests are inadequate for simulating the real-world loading that a component may experience in its life cycle. Therefore, this project’s goal was to develop a low-cost biaxial testing apparatus using off-the-shelf components, including the Arduino Uno microcontroller (“Arduino”), stepper motors (“motors”), and load cell. This report outlines the development of the software required to</div><div>operate the motors and read output value of the load cell. The Arduino code used to control the motors was developed using open-source code available on GitHub and the Stepper library, which contains the required functions for controlling the motors. The Arduino code can be used</div><div>to determine the strain rate of up to 11 𝑚𝑚/𝑚𝑖𝑛, as well as the type of loading (tension or compression) along each axis. </div>

Sheep Sclera Soft Tissue Subjected to Mechanical Equi-Biaxial Testing

A better understanding of diseases progress in tissues vest on the accurate understanding of tissues under mechanical loading. Also, development of therapies for injuries may depend on the available mechanical data for soft tissues. In this study, the raw data of biaxial tensile testing of sclera soft tissue is presented in this paper. Biaxial mechanical testing of soft tissues presents details understanding of how soft tissues behave when compared to uniaxial testing. Biomechanical properties of soft tissues are vital in the development of accurate computational models. Reliable computational models of studying mechanisms of diseases depends mainly on the accurate and more details mechanical behavior of soft tissues. These accurate and detailed computational models may be utilized to further develop the understanding and therapies of various diseases. The mechanical tensile testing was conducted on the passive sheep sclera. Engineering stress vs strain of several samples of the sheep sclera are further presented determined from force and displacement experimental data. The goal of this paper is to make available biaxial data of sheep sclera soft tissue that can be further utilized.

Heterogeneity of Ex Vivo and In Vivo Properties along the Length of the Abdominal Aortic Aneurysm

The current clinical guidelines for the management of aortic abdominal aneurysms (AAAs) overlook the structural and mechanical heterogeneity of the aortic tissue and its role in the regional weakening that drives disease progression. This study is a comprehensive investigation of the structural and biomechanical heterogeneity of AAA tissue along the length and circumference of the aorta, by means of regional ex vivo and in vivo properties. Biaxial testing and histological analysis were performed on ex vivo human aortic specimens systematically collected during open repair surgery. Wall-shear stress and three-dimensional principal strain analysis were performed to allow for in vivo regional characterization of individual aortas. A marked effect of position along the aortic length was observed in both ex vivo and in vivo properties, with the central regions corresponding to the aneurysmal sac being significantly different from the adjacent regions. The heterogeneity along the circumference of the aorta was reflected in the ex vivo biaxial response at low strains and histological properties. Present findings uniquely show the importance of regional characterization for aortic assessment and the need to correlate heterogeneity at the tissue level with non-invasive measurements aimed at improving clinical outcomes.

Paired PV Loop Analysis and Biaxial Mechanical Testing Characterize Differences in Left Ventricular Tissue Stiffness of Volume Overload and Angiotensin-Induced Pressure Overload Hearts

Pressure overload (PO) and volume overload (VO) of the heart result in distinctive changes to geometry, due to compensatory structural remodeling. This remodeling potentially leads to changes in tissue mechanical properties. Understanding such changes is important, as tissue modulus has an impact on cardiac performance, disease progression, and influences on cell phenotype. Pressure-Volume (PV) loop analysis, a clinically-relevant method for measuring left ventricular (LV) chamber stiffness, was performed in vivo on control rat hearts and rats subjected to either chronic PO (4-weeks) or VO (8-weeks). Immediately following PV loops, biaxial testing was performed on LV free wall tissue to directly measure tissue mechanical properties. The ß coefficient, an index of chamber stiffness calculated from the PV loop analysis, increased 98% in PO (n=4) and decreased 38% in VO (n=5) compared to control (n=6). Material constants of LV walls obtained from ex vivo biaxial testing (n =10), were not changed in PO, and decreased by about half in VO compared to control. PV loop analysis showed the expected increase in chamber stiffness of PO and expected decrease in chamber stiffness of VO. Biaxial testing showed a decreased modulus of the myocardium of the VO model, but no changes in the PO model, this suggests the increased chamber stiffness in PO, as shown in the PV loop analysis, may be secondary to changes in tissue mass and/or geometry but not an increase in passive tissue mechanical properties.

Determining the Damage and Failure Behaviour of Textile Reinforced Composites under Combined In-Plane and Out-of-Plane Loading

The absence of sufficient knowledge of the heterogeneous damage behaviour of textile reinforced composites, especially under combined in-plane and out-of-plane loadings, requires the development of multi-scale experimental and numerical methods. In the scope of this paper, three different types of plain weave fabrics with increasing areal weight were considered to characterise the influence of ondulation and nesting effects on the damage behaviour. Therefore an advanced new biaxial testing method has been elaborated to experimentally determine the fracture resistance at the combined biaxial loads. Methods in image processing of the acquired in-situ CT data and micrographs have been utilised to obtain profound knowledge of the textile geometry and the distribution of the fibre volume content of each type. Combining the derived data of the idealised geometry with a numerical multi-scale approach was sufficient to determine the fracture resistances of predefined uniaxial and biaxial load paths. Thereby, Cuntze’s three-dimensional failure mode concept was incorporated to predict damage and failure. The embedded element method was used to obtain a structured mesh of the complex textile geometries. The usage of statistical and visualisation methods contributed to a profound comprehension of the ondulation and nesting effects.