Dynamic Testing Techniques Research Articles

Sequential Thiol Click Reactions: Formation of Ternary Thiourethane/Thiol–Ene Networks with Enhanced Thermal and Mechanical Properties

We report the physical properties of thiol-ene networks modified with thiourethane or urethane linkages, either along the main chain or as a branched component in the network, respectively. Because of the robust and orthogonal nature of thiol-isocyanate and thiol-ene reactions, these networks can be formed in a two-step, one-pot synthesis. Resultant networks were characterized using dynamic mechanical analysis, mechanical testing and other complementary techniques. It was found that incorporating (thio)urethanes into the networks increased Tg, but also increased strain at break and toughness while decreasing cross-link density. The changes in physical properties are discussed in terms of a proposed dual network morphology. These facile modifications to thiol-ene networks demonstrate how molecular-level, nanoscale changes can have a profound influence on the macroscale properties through hierarchical development of network morphology.

Test case design algorithm for basic path test

McCabe's basic path testing method( McCABE T J. A complexity measure. IEEE Transactions on Software Engineering, 1976, SE-2( 4) : 308- 320) is a more rigorous software testing one in dynamic white-box testing techniques, but the efficiency of McCabe method is lower. To solve this problem, this paper proposed an algorithm to design basic path test case according to the basic program structure. The algorithm first created a basic unit chart based on the Z-path coverage.Next, the rules that combined a control flow graph from basic unit were established. On this basis, the combination algorithm of the basic path was constructed. The algorithm collected the path set of basic program structure by scanning a program only once, and then generated the basic path set using those paths by combination ways. This method is more concise than the method proposed by McCabe, and it can improve the efficiency of the basic path test case design.

A dynamic technique for the measurement of thermal conductivity of molten salt based on cylindrical melting model

This paper reports a dynamic testing technique for measuring the effective thermal conductivity of phase change materials close to the melting point aiming at the compensation for the absence of such data. Based on Stefan model, the time dependence of the position of the phase interface in a cylindrical melting process, which implies the thermal conductivity, was successfully determined with the aid of the perturbation method. Thereafter, a series of experiments were conducted on a well-designed testing system with excellent heat insulation to collect relevant data of sodium acetate trihydrate. To bridge the gap between the experimental and the actual values, a 3-dimensional, unsteady, numerical model, taking convection into consideration, was built on CFD code. Under necessary assumptions, this model allowed a better understanding of the role of the convection playing in the experiments. Accurate results of approximation to experimental data were obtained by continually adjusting the iterative value. The maximum deviation was limited in 9 %.

A Review of Dynamic Experimental Techniques and Mechanical Behaviour of Rock Materials

The purpose of this review is to discuss the development and the state of the art in dynamic testing techniques and dynamic mechanical behaviour of rock materials. The review begins by briefly introducing the history of rock dynamics and explaining the significance of studying these issues. Loading techniques commonly used for both intermediate and high strain rate tests and measurement techniques for dynamic stress and deformation are critically assessed in Sects. 2 and 3. In Sect. 4, methods of dynamic testing and estimation to obtain stress–strain curves at high strain rate are summarized, followed by an in-depth description of various dynamic mechanical properties (e.g. uniaxial and triaxial compressive strength, tensile strength, shear strength and fracture toughness) and corresponding fracture behaviour. Some influencing rock structural features (i.e. microstructure, size and shape) and testing conditions (i.e. confining pressure, temperature and water saturation) are considered, ending with some popular semi-empirical rate-dependent equations for the enhancement of dynamic mechanical properties. Section 5 discusses physical mechanisms of strain rate effects. Section 6 describes phenomenological and mechanically based rate-dependent constitutive models established from the knowledge of the stress–strain behaviour and physical mechanisms. Section 7 presents dynamic fracture criteria for quasi-brittle materials. Finally, a brief summary and some aspects of prospective research are presented.

Evaluation of a substructured soft-real time hybrid test for performing seismic analysis of complex structural systems

The hybrid test method is a relatively recently developed dynamic testing technique that uses numerical modelling combined with simultaneous physical testing. The concept of substructuring allows the critical or highly nonlinear part of the structure that is difficult to numerically model with accuracy to be physically tested whilst the remainder of the structure, that has a more predictable response, is numerically modelled. In this paper, a substructured soft-real time hybrid test is evaluated as an accurate means of performing seismic tests of complex structures. The structure analysed is a three-storey, two-by-one bay concentrically braced frame (CBF) steel structure subjected to seismic excitation. A ground storey braced frame substructure whose response is critical to the overall response of the structure is tested, whilst the remainder of the structure is numerically modelled. OpenSees is used for numerical modelling and OpenFresco is used for the communication between the test equipment and numerical model. A novel approach using OpenFresco to define the complex numerical substructure of an X-braced frame within a hybrid test is also presented. The results of the hybrid tests are compared to purely numerical models using OpenSees and a simulated test using a combination of OpenSees and OpenFresco. The comparative results indicate that the test method provides an accurate and cost effective procedure for performing full scale seismic tests of complex structural systems.

Impact-induced initiation and energy release behavior of reactive materials

Reactive material fragment is an extremely efficient damage enhancement technology that incorporates the defeat mechanisms of kinetic energy and chemical energy. In this paper, the polymer-based reactive material fragment/target interactions are investigated. Related dynamic testing techniques for energy release characteristics of reactive material fragments are presented, and a series of ballistic experiments is conducted. The results show the reactive material fragment, which perforates the closed test chamber, undergoes a violent chemical reaction under highly dynamic loads and releases great amounts of thermo-chemical energy on the interior. The impact-initiated process and energy release behavior are markedly influenced by the impact velocity, indicating the material’s fracture is of importance to the reaction. A relationship between the maximum pressure inside the chamber and the reaction efficiency is derived to analyze the influence quantitatively, and the venting effects are also considered.

The Effect of Woven Structures on the Vibration Characteristics of Glass Fabric/Epoxy Composite Plates

<p class="MsoNormal" style="text-justify: inter-ideograph; margin: 0cm 0cm 0pt; layout-grid-mode: char; text-align: justify; mso-layout-grid-align: none;"><span style="font-size: 9pt; mso-fareast-language: ZH-CN; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US;" lang="EN-US"><span style="font-family: Times New Roman;">We study the effects of woven structures on the dynamic mechanical properties and vibration properties of the fabric composites. Five typical weaving sets including the ordinary plain weaved and the warp interlocked were adopted in fabric processing. The composites plates with the same thickness were prepared by epoxy resin curing, and their fibre volume fractions were examined. Dynamic Mechanical Analyzer (DMA) and vibration test technique were used to reveal the dynamical behaviours of specimens in different frequencies of vibration. The storage modulus, the loss tangent, the natural frequency and damping ratio<span style="mso-spacerun: yes;"> </span>were obtained. The result showed that the woven structure have a strong effect on the fibre volume fraction, resin-rich area and the warp architectures of the composites, which determines the performances of the composites in vibration.</span></span></p><p class="MsoNormal" style="text-justify: inter-ideograph; margin: 0cm 0cm 0pt; layout-grid-mode: char; text-align: justify; mso-layout-grid-align: none;"><span style="font-size: 9pt; mso-fareast-language: ZH-CN; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US;" lang="EN-US"><span style="font-family: Times New Roman;"><strong>Defence Science Journal, 2011, 61(5), pp.499-504</strong><strong><strong>, DOI:http://dx.doi.org/10.14429/dsj.61.296</strong></strong><br /></span></span></p>

On the assessment of passive devices for structural control via real-time dynamic substructuring

In this work, the applicability of a dynamic testing technique known as real-time dynamic substructuring (RTDS) for the assessment of passive vibration suppression systems in seismic protection of buildings is analysed. RTDS is an efficient method for the assessment of dynamic and rate-dependent behaviour of systems subjected to dynamic excitation at real scale and in real scenarios. The actuators used in RTDS test introduce additional undesirable dynamics into the system, which are often not fully compensated for in the actuator controller—these dynamics are commonly approximated as a feedback delay. To guarantee the validity and accuracy of an RTDS simulation, a stability analysis of the substructured system that includes the feedback delay should be carried out. In this paper, we present explicit analyses that provide a dynamic characterization of the delay-induced phenomena in RTDS simulations when considering passive vibration suppression systems with strong nonlinearities. We present a complete set of closed-form expressions to describe the main phenomena because of delay in terms of dynamic stability in an RTDS simulation. Through an experimental study, we confirm the existence of self-sustained oscillations caused by very small delay in the feedback loop. This lead the system to instability in the form of high-frequency oscillations. Copyright © 2011 John Wiley & Sons, Ltd.

A Critical Assessment of Dynamic Rock Reinforcement and Support Testing Facilities

A major engineering challenge for mines experiencing significant seismicity is the performance of the support systems. This paper provides a critical review of dynamic testing techniques used for understanding and quantifying the performance of ground support systems. This review focuses on testing rigs in Canada, Australia and South Africa. The different laboratory testing rigs are listed along with their characteristics and their advantages and disadvantages. The paper concludes with recommendations towards developing a more unified strategy to understand and eventually forecast the behaviour of support systems under dynamic loads.

Vibration characteristics of glass fabric/epoxy composites with different woven structures

We study the effects of woven structures on the vibration properties of the composites. Five typical weaving sets including the ordinary plain weaved and the warp interlocked were adopted in fabric processing. The composites plates with adequate thickness were prepared by epoxy resin curing, and their fiber volume fractions were examined. Dynamic mechanical analyzer and vibration test technique were used to reveal the dynamical behaviors of specimens in different frequencies of vibration. The result showed that the woven structure have a strong effect on the fiber volume fraction, resin-rich area, and the warp architectures of the composites, which determine the performances of the composites in vibration.

Forensic Engineering Analysis Of Bicycle Versus Pickup Collision

The Forensic Engineering Analysis Of Bicycle-Vehicle Incidents Presents Its Own Unique Set Of Challenges. Often, The Forensic Engineer Is Faced With A Limited Data Set For Determining Vehicle Impact Speed From The Physical Evidence Produced By A Bicycle Collision With An Automobile, Which May Not Be Of Issue For A Vehicle-To-Vehicle Collision At Similar Speeds. This Paper Analyzes A Collision Between A Light Duty Pickup Pulling A Tandem Axle Utility Trailer And A Bicycle Ridden By A Minor Child. There Were Allegations That The Pickup Was Traveling At A High Speed Above The Speed Limit, As Well As Passing Another Vehicle At The Time Of The Incident. In Order To Accurately And Dependably Determine The Speed Of The Ford F350 Pickup Involved In This Incident Event, This Forensic Engineer Elected To Recreate The Vehicle Locked Wheel Skidding Evidence That Was Produced During The Incident Event And Photographically Recorded By Police Investigators. The Dynamic Skid Testing Technique, Test Equipment, And General Test Procedures Used To Accurately Determine Vehicle Speeds For This Incident Event, And How It Can Be Applied To Similar Collision Events Are Discussed In This Paper

Plastic bulging of sheet metals at high strain rates

The biaxial bulge test is a material test for sheet metals to evaluate formability and determine the flow stress diagram. Due to the biaxial state of stress induced in this test, the maximum achievable strain before fracture is much larger than in the uniaxial tensile test. A new dynamic bulge testing technique is simulated and analyzed in this study which can be performed on a conventional split Hopkinson pressure bar (SHPB) system to evaluate the strain-rate dependent strength of material at high impact velocities. Polyurethane rubber as pressure carrying medium is used to bulge the OFHC copper sheet. The use of hyperelastic rubber instead of fluid as a pressure medium makes the bulge test simple and easy to perform. The input bar of SHPB is used to apply and measure the bulging pressure. The finite element simulation using ABAQUS/explicit and analytical analysis are compared and show good correlation with each other. The results clearly show that as the strain-rate increases, the strength of the OFHC copper increases. From the study, a robust method to determine the material behavior under dynamically biaxial deformation conditions has been developed.

English

Improving software reliability of mission-critical systems is widely recognised as one of the major challenges. Early detection of errors in software requirements, designs and implementation, need rigorous verification and validation techniques. Several techniques comprising static and dynamic testing approaches are used to improve reliability of mission critical software; however it is hard to balance development time and budget with software reliability. Particularly using dynamic testing techniques, it is hard to ensure software reliability, as exhaustive testing is not possible. On the other hand, formal verification techniques utilise mathematical logic to prove correctness of the software based on given specifications, which in turn improves the reliability of the software. Theorem proving is a powerful formal verification technique that enhances the software reliability for missioncritical aerospace applications. This paper discusses the issues related to software reliability and theorem proving used to enhance software reliability through formal verification technique, based on the experiences with STeP tool, using the conventional and internationally accepted methodologies, models, theorem proving techniques available in the tool without proposing a new model. Defence Science Journal, 2009, 59(3), pp.314-317 , DOI:http://dx.doi.org/10.14429/dsj.59.1527

Molecular engineering and properties of chitin based shape memory polyurethanes

Shape memory polyurethanes (SMPUs) are playing a prominent role in biomedical, self repairing, aerospace and smart materials. Shape memory polyurethanes (SMPUs) were prepared from polycaprolactone diol 4000 (PCL4000), 1-4-butanediol (BDO), chitin, dimethylol propionic acid (DMPA), triethylamine (TEA), and 4, 4′-diphenylmethane diisocyanate (MDI). Trifunctional characteristics of chitin enhanced the thermal and mechanical properties of SMPUs. DMPA was used to obtain higher recovery and lower residual strain. The morphology, microstructure, mechanical, thermo-mechanical, and shape memory properties of synthesized SMPUs were investigated using Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), dynamic mechanical thermal analyzer (DMTA) and tensile testing techniques. The results showed that crosslinked SMPUs have better thermal and thermo-mechanical properties, and a good shape memory effect.

Rehabilitation assessment of a steel railway bridge by dynamic field testing

The seven-span steel railway bridge crossing the River Nile near Qanater, Egypt, has been reported to have excessive sway under the current railway traffic loads. A rehabilitation plan has been made previously to preserve and enforce the structural condition of this main bridge. Dynamic testing techniques were used here to evaluate the modal properties of the bridge system at different stages of the repair plan. Ambient vibration measurements together with measurements after the passage of trains were conducted. The dynamic parameters of the bridge were extracted using both the Frequency Domain Decomposition (FDD) and the Eigen Realization Algorithm (ERA) techniques. Comparisons were made to understand the basic behaviour of the bridge and to evaluate the effectiveness of the current repair method. The modification in the stiffness of the bridge due to rehabilitation was evaluated. The current rehabilitation strategy proved effective; as a result of this study, further recommendations are made.

Dynamic analysis and design of a high voltage circuit breaker with spring operating mechanism

Spring Operating Mechanism (SOM) is a dynamic system to open and close the circuit breaker in a voltage controlling system. For a high-speed action of opening and closing within a few mili-seconds, a SOM consists of many links, joints, chains, and cams. Thus, various dynamic characteristics are occurred, especially large contact forces between the cam and the roller, the shaft and the stopper. To save time and money for a new design of SOM system, analysis of the mechanism is necessary. In this paper, a multibody dynamic analysis and test technique was applied for a SOM to predict, estimate and validate forces occurring during the operation. For the multibody dynamic analysis, the ADAMS program was employed for 145kV circuit breaker with a SOM. For an accurate modeling, several components were sequentially added and the reliability of modeling was validated through the comparison with test data of opening and closing.

Dynamic tensile testing of plastic materials

Dynamic tensile tests were carried out using a servo-hydraulic machine on four representative plastic materials following a practice guideline by the Society of Automotive Engineers (SAE). The experimental results generated this way were ranked as “good” using the qualitative measure provided in the guideline. To advance our understanding of dynamic tensile tests, the validity of the dynamic tensile tests was investigated by examining the condition of dynamic stress equilibrium; a criterion used in split Hopkinson pressure bar (SHPB) tests. The results show that the quantitative criterion for a valid SHPB test is also applicable to dynamic tensile tests and it is an unbiased method as compared to the qualitative method used in the current practice. Another issue in dynamic material testing using a tensile testing machine is system ringing. The testing system was analyzed using a basic vibration model. The analytical solutions were obtained for the one-degree freedom spring-mass model with and without a damper. The mathematical model provided descriptions about the influence of the loading rate and the natural frequency of the testing system on the magnitude of system ringing and its decay rate. It illustrated that the maximum strain rate at which a testing system can be used to generate acceptable data are limited by the natural frequency of the testing system. The analysis results agreed well with the empirical relationships established based on experimental evidence. For the first time, this work advances the dynamic tensile testing technique from its current empirical stage to an analysis-based level.

Biaxial Testing of Sheet Materials at High Strain Rates Using Viscoelastic Bars

A dynamic bulge testing technique is developed to perform biaxial tests on metals at high strain rates. The main component of the dynamic testing device is a movable bulge cell which is directly mounted on the measuring end of the input bar of a conventional split Hopkinson pressure bar system. The input bar is used to apply and measure the bulging pressure. The experimental system is analyzed in detail and the measurement accuracy is discussed. It is found that bars made of low impedance materials must be used to achieve a satisfactory pressure measurement accuracy. A series of dynamic experiments is performed on aluminum 6111-T4 sheets using viscoelastic nylon bars to demonstrate the capabilities of the proposed experimental technique. The parameters of the rate-dependent Hollomon–Cowper–Symonds J2 plasticity model of the aluminum are determined using an inverse analysis method in conjunction with finite element simulations.

A SHOCK TUBE?BASED FACILITY FOR IMPACT TESTING

Abstract : Many dynamic testing techniques use gas guns as a pressure generator. The pressure generated from the gas guns is often of low velocity and low energy and has a relatively random or short duration of a uniform pressure level. This kind of pressure is not well defined and cannot be converted into other application conditions. With aims at improving experimental capability and expanding the research horizon, a shock tube was designed and constructed; and innovative applications were explored. With proper adjustments of gas components and gas pressures, well-defined pressure sources could be produced. With appropriate designs of a force transformer, various testing parameters required for different, dynamic experiments could also be simulated. In this paper, a piston-like impactor was inserted into the shock tube as a pressure transformer. The feasibility of using the shock-tube-based facility for impact testing was demonstrated.

The stiffness of natural London Clay

An investigation of natural London Clay is reported involving advanced triaxial, hollow cylinder apparatus (HCA) and dynamic testing techniques. Significant anisotropy was revealed at all scales of deformation, and the framework of cross-anisotropic elasticity was found to apply broadly to the initial elastic behaviour. The stiffness parameters obtained by independent techniques generally exhibited good agreement, with the greatest deviation being seen in the Poisson's ratios, which fell far from the values usually assumed in conventional foundation analysis. Probing tests established the limits to the elastic domain over a range of depths, showing that these scaled in proportion to the mean effective stress level, as did those of a second kinematic surface that surrounded the elastic domain. Once engaged, this second surface signified a new pattern of strain increment directions, faster elastic-plastic stiffness decay with strain, and also a greater dependence of behaviour on recent stress history. However, the two kinematic surfaces cover a relatively small proportion of the admissible stress space, and behaviour at larger strains is both anisotropic and strongly non-linear, features that affect profoundly the soil displacements induced by geotechnical construction in this deposit.