Experimental Evaluation of Tension and Shear Responses of Material Discontinuities in Origami-Based Sheet Metal Bending

Origami-based sheet metal (OSM) bending uses the origami concept to form a three-dimensional (3D) structures from a two-dimensional (2D) sheet by a series of bending operation. The OSM bending relies on a material discontinuity (MD) to perform the bending operation where the MDs are subjected to tension and shear load. Even though the OSM bending is a process that is simple, cost-effective, and easy to integrate into mass production, the understanding of the OSM bending mechanics is limiting its wide application. Particularly, the deformation behavior of MDs under tension and shear load remains unknown. Hence, this work investigates the response of MDs to these loads using the standard tension and shear tests. From the tests, critical values for two different ductile fracture criteria (DFC) are determined, and the possibility of a failure occurring in OSM bending is predicted. Results show that the load-bearing capability of the MDs is related to change in the effective cross-section area of a MD. Simple tension and shear tests can provide a simple procedure to predict failure in OSM bending. The impact of self-contact occurred under shear load influences maximum shear force and accuracy of failure prediction.

PECULIARITIES OF WORK OF PROFILE PRODUCTS FROM COMPOSITE MATERIALS IN BUILDING CONSTRUCTIONS LOCATED IN SEISMIC AREAS

Purpose. The aim of the article is to reveal during the analysis the peculiarities of the work of profile products from composite materials in building structures located in seismic areas. Methodology. The structure of fiber-reinforced composite materials is given and the role of each component is explained. It is noted that recently, in the construction industry for the manufacture of basic and additional structures, composite materials are used not only on the basis of epoxy resins reinforced with glass fiber, but also on the basis of carbon, organic and other fibrous fillers. The expediency of the application of products from composite materials in the construction is highlighted. Findings. The analysis of literary sources devoted to the work of products from composite materials of simple and complex cross-section in the building structures under the influence of simple (tension, compression, torsion) and complex types of loading was conducted. Distribution of stresses acting in cross-sections of complex profile rod elements made of composite materials under bending load is shown. Features of work of profile products from composite materials in building constructions are revealed. The reasons of decrease of load-carrying ability of complex profile products made of composite materials are determined. The existing methods of increasing mechanical characteristics of products from composite materials are given. Negative consequences and disadvantages of application of existing methods of increasing mechanical characteristics of products from composite materials are formulated. Originality. On the basis of the carried out analysis conclusions about necessity of refinement of existing methods of increase of mechanical characteristics of products from composite materials are made. Practical value. During the analysis features of work of profile products from composite materials in building constructions which are the basis for development of new ways of increasing mechanical characteristics of products from composite materials in building constructions and improvement of already existing ones are revealed.

Application of the concept of criterion of a complex stress state to a simple tension for appraisal of resistance of fatigue of structural materials. Part 2. Drawing up criterion and its checking on compliance to experimental data

The criterion for appraisal of resistance of fatigue of structural material at action on it of repeatedly variables loads and static loads in the form of a bend or tensioncompression together with torsion, and also at action of loads, which create two-axis regular change of stress state in a dangerous point of material is constructed. The received criterion will acceptable be coordinated with the known experimental data. Keywords: dangerous point of material, regular cycle of loading, equivalent amplitude, equivalent average stress, chart of extreme amplitudes of stresses. [email protected]

Application of the concept of the criterion of equivalence of complex stress state to simple tension for assessing the fatigue resistance of structural materials. Part 1. Review of some experimental data with the preparation of the necessary information for subsequent use

A brief overview of the features of the fatigue resistance of some steels is given with the selection of terms, concepts and numerical data necessary for the subsequent compilation and verification of the equivalence criterion in relation to assessing the ability of structural materials to resist fatigue for a long time under the action of certain combinations of alternating and static loads. Keywords: regular loading cycle, extremely stressed state, static stressed state, bending, torsion, biaxial static tension. [email protected]

Anisotropic stress softening of residually stressed solids

Residual stress in purely elastic solids has been extensively studied in the literature. However, to the best of the author’s knowledge, the influence of residual stresses on anisotropic Mullins materials has not been studied. Hence, the aim of this paper is to propose an anisotropic phenomenological model to describe the Mullins phenomena for residually stressed elastomers; taking note that most materials are not purely elastic and some of them exhibit an anisotropic stress-softening phenomenon widely known as the Mullins effect. The anisotropic model is based on the use of direction-dependent damage parameters and a set of anisotropic spectral invariants presented recently in the literature by the author. The spectral invariants have a clear physical meaning that is useful in aiding the design of a rigorous experiment to construct a specific form of constitutive equation. Since boundary value results for residually stressed Mullins material are not found in the literature, the effect of residual stresses on the Mullins phenomena in simple tension, torsion and equibiaxial deformations is discussed in this paper.

Modelling of Flexible Adhesives in Simple Mechanical States with the Use of the Darijani–Naghdabadi Strain Tensors and Kirchhoff–de Saint-Venant Elastic Potential

Practical aspects of modelling of flexible adhesives with the energy conjugate measures of stress and strain of the Darijani–Naghdabadi (D-N) family are discussed. A possibility of description of materials exhibiting non-linear physical characteristics with the use of non-linear geometric relationships and linear elastic constitutive law is considered. Nominal stress vs. stretch relations are specified in cases of simple tension and simple shear with the use of the Kirchhoff–de Saint-Venant elastic potential and D-N energy conjugate stress and strain measures. Obtained theoretical estimates were compared with experimental results of simple tension and simple shear tests performed on Sika PM polyurethane (Cracow, Sika Poland). The deformation rate was fixed in order to minimize the influence of viscosity. Values of parameters in the definition of the D-N strain tensor were optimized in order to provide good agreement between model predictions and experimental results. Observed discrepancies indicate that the proposed approach is not appropriate for constitutive modelling of the PM polymer. The presented approach is proposed to be used as a simple design model providing practical formulas describing the behavior of materials of non-linear characteristics in chosen mechanical states. Admissible values of exponents are discussed regarding its bijectivity in a limited range of variation of principal stretches.

Local One-Sided Rubber Bulging Test to Measure Various Strain Paths of Metal Tube

We proposed a local one-sided rubber bulging method of metal tubes to evaluate various strain paths at an aimed portion and measured the forming limit strains of metal tubes at the place of the occurrence of necking under biaxial deformation. Using this method, since rubber is used to give pressure from the inner side of the tube, no sealing mechanisms were necessary unlike during hydraulic pressure bulging. An opening was prepared in front of the die to locally bulge a tube at only the evaluation portion. To change the restriction conditions of the bulged region for biaxial deformation at the opening, a round or square cutout, or a slit was introduced. The test was conducted using a universal compression test machine and simple dies rather than a dedicated machine. Considering the experimental results, it was confirmed that the strain path was varied by changing the position and size of slits and cutouts. Using either a cutout or a slit, the strain path in the side of the metal tubes can be either equi-biaxial tension or simple tension, respectively. Additionally, by changing the size of the cuts or slits, the strain path can be varied.

Identification of thermal material parameters for thermo-mechanically coupled material models

The possibility of accurately identifying thermal material parameters on the basis of a simple tension test is presented, using a parameter identification framework for thermo-mechanically coupled material models on the basis of full field displacement and temperature field measurements. Main objective is to show the impact of the material model formulation on the results of such an identification with respect to accuracy and uniqueness of the result. To do so, and as a proof of concept, the data of two different experiments is used. One experiment including cooling of the specimen, due to ambient temperature, and one without specimen cooling. The main constitutive relations of two basic material models are summarised (associated and non-associated plasticity), whereas both models are extended so as to introduce an additional material parameter for the thermodynamically consistent scaling of dissipated energy. The chosen models are subjected to two parameter identifications each, using the data of either experiment and focusing on the determination of thermal material parameters. The influence of the predicted dissipated energy of the models on the identification process is investigated showing that a specific material model formulation must be chosen carefully. The material model with associated evolution equations used within this work does neither allow a unique identification result, nor is any of the solutions for the underlying material parameters close to literature values. In contrast to that, a stable, that is locally unique, re-identification of the literature values is possible for the boundary problem at hand if the model with non-associated evolution equation is used and if cooling is included in the experimental data.