Selected Papers from Experimental Stress Analysis 2020

This Special Issue consists of selected papers from the Experimental Stress Analysis 2020 conference. Experimental Stress Analysis 2020 was organized with the support of the Czech Society for Mechanics, Expert Group of Experimental Mechanics, and was, for this particular year, held online in 19–22 October 2020. The objectives of the conference included identification of current situation, sharing professional experience and knowledge, discussing new theoretical and practical findings, and the establishment and strengthening of relationships between universities, companies, and scientists from the field of experimental mechanics in mechanical and civil engineering. The topics of the conference were focused on experimental research on materials and structures subjected to mechanical, thermal–mechanical, and dynamic loading, including damage, fatigue, and fracture analyses. The selected papers deal with top-level contemporary phenomena, such as modern durable materials, numerical modeling and simulations, and innovative non-destructive materials’ testing

Mechanical Engineering

The book substantially offers the latest progresses about the important topics of the "Mechanical Engineering" to readers. It includes twenty-eight excellent studies prepared using state-of-art methodologies by professional researchers from different countries. The sections in the book comprise of the following titles: power transmission system, manufacturing processes and system analysis, thermo-fluid systems, simulations and computer applications, and new approaches in mechanical engineering education and organization systems

DEVELOPMENT OF A CONTINUOUS-TENSION-COMPRESSION MACHINE FOR TESTING THIN SHEET METAL

This thesis details the design and manufacturing of a custom testing machine for thin sheet metal undergoing continuous tension-compression (CTC) loading. The CTC machine concept is based on using a set of intermeshing dies to continuously support the thin sheet specimen against buckling during the test. The upper set of dies are held in place by a pneumatic actuator of 25 kN capacity. The dies can move freely relative to one another, so that both tension and compression can be performed in the same setup. A hydraulic actuator of 50 kN capacity displaces one side of the intermeshed dies. The stroke of the actuator is 63.5 mm, and based on the geometry of the CTC machine and specimen selected, that results into 20% strain in compression and 75% in tension. Strain is measured on the specimen itself using high-elongation strain gages, capable of reaching up to 20-30%, depending on the material. However, based on the hardware currently used, only +/- 5% strain can be read; this is an issue that can be easily fixed with updates to measurement hardware. Chapter 1, which is the introduction, includes the motivation behind this work, as well as other concepts that have been implemented to achieve similar results. Chapter 2 describes the mechanical design of the CTC machine. It includes details of the machine design and functionality, and the strength calculations performed to verify its correct and safe operation. Chapter 3 details the custom data acquisition and control system that was developed. It includes details of the sensors and circuity used for the CTC machine. It also discusses the user interface of the control software, and the pre-programmed functionality of the CTC machine. Chapter 4 describes a full suite of verification tests that were performed on both the CTC machine and CTC specimen geometry, to ensure that the data acquired is accurate and reliable. After the verification testing, Chapter 5 describes a series of cyclic experiments performed on a variety of thin metallic sheets. The research chapters of the thesis are capped by Chapter 6, which discusses a non-linear kinematic hardening model of the Chaboche family, which can be used to replicate the results of the cyclic experiments. Finally, Chapter 7 provides a summary of this work, the main conclusions, as well as proposed future extensions and improvements of the CTC machine. Returning to Chapter 4, the verification tests performed for the CTC machine itself involve tension tests on ASTM E8 specimens using both the present machine and a MTS Landmark 370 servohydraulic loading frame. The agreement is found to be excellent. The CTC specimen geometry is different from the standard ASTM E8 dogbone specimen one, to further prevent buckling during compression. It is confirmed though that the CTC specimen geometry provides identical results to the standard ASTM E8 during tension testing. In summary, the results listed in Chapter 4 show favorable agreement between the two machines, as well as the two specimen geometries. The cyclic experiments discussed in Chapter 5 are performed on a variety of thin metallic sheets: aluminum alloy AA6022-T43 as well as EDDQ, JAC-270D, DP590, DP980 and DP1180 steels. An example of a cyclic experiment is: straining a specimen in tension to +1% engineering strain, reverse loading to -1%, forward loading to +3%, etc. as in -3%, +5%, -5%, then back to 0%. Another experiment is cyclic loading between two equal and opposite strain values, e.g., +/- 2%, for N number of cycles. A noticeable trend with all the materials tested is the amount of tension/compression asymmetry, i.e., where the compressive flow stress is higher than the one in tension for pure compression or tension tests. The Chaboche model in Chapter 6, is calibrated for DP980 steel. An automated parameter determination algorithm, implemented in Matlab, is also described. The code produced is meant to provide the user with an initial best fit to the experiment, so that the user can then improve the fit further as desired, e.g., by manual adjustments. It is expected that utilizing this model in numerical simulations of sheet metal forming processes that include unloading and/or cyclic loading can yield accurate predictions of the springback expected

Micromechanics of Fiber Networks Including Nonlinear Hysteresis and its Application to Multibody Dynamic Modeling of Piano Mechanisms

Many engineering applications make use of fiber assemblies under compression. Unfortunately, this compression behavior is difficult to predict, due to nonlinear compliance, hysteresis, and anelasticity. The main objective of this research is to develop an algorithm which is capable of incorporating the microscale features of the fiber network into macroscopic scale applications, particularly the modeling of contact mechanics in multibody systems. In micromechanical approaches, the response of a fiber assembly to an external force is related to the response of basic fiber units as well as the interactions between these units, i.e. the mechanical properties of the constituent fibers and the architecture of the assembly will both have a significant influence on the overall response of the assembly to compressive load schemes. Probabilistic and statistical principles are used to construct the structure of the uniformly-distributed random network. Different micromechanical approaches in modeling felt, as a nonwoven fiber assembly with unique mechanical properties, are explored to gain insight into the key mechanisms that influence its compressive response. Based on the deformation processes and techniques in estimating the number of fiber contacts, three micromechanical models are introduced: (1) constitutive equations for micromechanics of three-dimensional fiberwebs under small strains, in which elongation of the fibers is the key deformation mechanism, adapted for large deformation ranges; (2) micromechanical model based on the rate theory of granular media, in which bending and torsion of fibers are the predominant elemental deformations used to calculate compliances of a particular contact; and (3) a mechanistic model developed using the general deformation theory of the fiber networks with fiber bending at the micro level and a binomial distribution of fiber contacts. A well-established mechanistic model, based on fiber-to-fiber friction at the micro level, is presented for predicting the hysteresis in compression behavior of wool fiberwebs. A novel algorithm is introduced to incorporate a hysteretic micromechanical model - a combination of the mechanistic model with microstructural fiber bending, which uses a binomial distribution of the number of fiber-to-fiber contacts, and the friction-based hysteresis idea - into the contact mechanics of multibody simulations with felt-lined interacting bodies. Considering the realistic case in which a portion of fibers slides, the fiber network can be treated as two subnetworks: one from the fibers with non-sliding contact points, responsible for the elastic response of the network, and the other consisting of fibers that slide, generating irreversible hysteresis phenomenon in the fiberweb compression. A parameter identification is performed to minimize the error between the micromechanical model and the elastic part of the loading-unloading experimental data for felt, then contribution of friction was added to the obtained mechanistic compression-recovery curves. The theoretical framework for constructing a mechanistic multibody dynamic model of a vertical piano action is developed, and its general validity is established using a prototype model. Dynamic equations of motion are derived symbolically for the piano action using a graph-theoretic formulation. The model fidelity is increased by including hammer-string interaction, backcheck wire and hammer shank flexibility, a sophisticated key pivot model, nonlinear models of bridle strap and butt spring, and a novel mathematical contact model. The developed nonlinear hysteretic micromechanical model is used for the hammer-string interaction to affirm the reliability and applicability of the model in general multibody dynamic simulations. In addition, dynamic modeling of a flexible hub-beam system with an eccentric tip mass including nonlinear hysteretic contact is studied. The model represents the mechanical finger of an actuator for a piano key. Achieving a desired finger-key contact force profile that replicates that of a real pianist's finger requires dynamic and vibration analysis of the actuator device. The governing differential equations for the dynamic behavior of the system are derived using Euler-Bernoulli beam theory along with Lagrange's method. To discretize the distributed parameter flexible beam in the model, the finite element method is utilized. Excessive vibration due to the arm flexibility and also the rigid-body oscillations of the arm, especially during the period of key-felt contact, is eliminated utilizing a simple grounded rotational dashpot and a grounded rotational dashpot with a one-sided relation. The effect on vibration behavior attributed to these additional components is demonstrated using the simulated model

Coupled Theoretical and Experimental Methods to Understand Growth and Remodeling of In Situ Engineered Vascular Grafts in Young and Aged Hosts

In 1975, Rodbard introduced the concept of mechanical homeostasis; that arteries have an inherent capacity to maintain homeostatic stress states by altering their morphology through a negative feedback mechanism in response to mechanical loads. More recently, this capacity has been leveraged to develop acellular, in situ tissue-engineered vascular grafts (iTEVGs) which promote host growth and remodeling (G&R) to develop new arteries (neoarteries) in the tissue's functional site (in situ). These grafts offer a much-needed option to address the lack of viable autologous conduits, difficulties in scaling traditional tissue engineered grafts, and the rising demand for bypass grafting in an aging population. One such acellular, poly (glycerol sebacate) (PGS) iTEVG developed by Wang et al. has demonstrated in situ mature elastin and collagen formation in young hosts. However, the trial and error nature of graft design, coupled with the lack of knowledge of fundamental mechanisms guiding neoarterial G&R impedes efforts to translate these successes across age and species. In this work, we take a coupled theoretical and experimental approach to understanding salient mechanisms guiding neoartery formation in young and aged hosts. We developed a mathematical model of graft degradation based on in vitro assessment of enzymatic degradation. Next, we translated successful neoartery development from a rat aorta to the substantially smaller, rat carotid artery. We determined that after three-months of remodeling, the neoartery has similar mechanical properties to those of the clinical gold standard, vein graft. We then successfully translated the iTEVG to an aged murine carotid model and assessed differences in mechanical, microstructural, and biological stages of neoarterial G&R in young versus aged hosts over the course of six months. Subsequently, a constrained mixture model-based G&R tool was developed, informed with these experimental data, and used to predict long-term neoarterial G&R response in both age groups. Finally, we identified a common mode of adverse remodeling in neoarteries - rupture and calcification. Motivated by these results, we developed new techniques to analyze calcification in a parallel, model system exhibiting similar modes of adverse remodeling - cerebral aneurysms. These results provide insights for future work developing strategies necessary to optimally design iTEVGs

Innovative solutions in bridge construction, rehabilitation, and structural health monitoring

This dissertation includes three technical papers that investigate the development of innovative technologies for bridge construction, rehabilitation, and structural health monitoring, respectively, at different stages of the technology transfer process...The research impact is twofold: first is the introduction of promising innovative technologies in development and implementation projects with the direct involvement of forward-thinking industry partners; second is the demonstration of the validity of these technologies on the basis of a rigorous scientific approach --Abstract, page iv

The Effect of Cooling Rate on the Microstructure Configuration of Continuously Cast Steel Slabs

This research work is another step for increasing the efficiency and productivity of the steel making process by enhancing both quality and quantity of the steel produced by the Continuous Casting process. When steels cool from a high temperature, austenite transforms into other phase configurations according to the austenite composition and cooling rate. As result of phase transformation, the steel crystal structure and, consequently, both the shape and the lattice parameter of the unit cell, change. These changes may introduce dilatational strains into the microstructure, which result in the creation of residual stress concentration zones within the microstructure. These stress concentration zones are vulnerable regions to the formation of microcracks or growth of the flaws in these regions. The main objective of this dissertation is to develop a method to define the optimum cooling rate for cooling continuously as-cast steel on industrial level. An FEM algorithm developed with the ANSYS codes is introduced in this dissertation to simulate the cooling of as-cast steel from any temperature below the solidification temperature. The algorithm is capable of being customized to simulate the thermodynamic behavior of as-cast steel microstructure with any chemical composition and any casting geometry imposed to desired cooling method. The phase transformation simulations were based on the CCT diagram and, therefore, they were quasi-real models. The models predict, analytically, the generation of the stress concentration regions due to the thermodynamic strains during cooling a sample from the austenite temperature range with different cooling rates. Another series of FEM models presented in this dissertation and post non-destructive tests (NDT) ultrasonic image analysis tests suggested in this work, can be used in the discussion of the effect of the cooling rate on the altering of the soundness of the tested steel. A combination of the suggested FEM algorithm and post image processing of NDT ultrasonic images along with laboratory cooling experiments and microstructural analysis provide a guideline to find the cooling rate for each grade of steel in the casting steel industry. Results of JMATPRO software also are deployed to increase the accuracy of the experimental set up and to obtain the required input data to run the proposed numerical algorithm cooling simulation