Dynamic Testing Techniques Research Articles

Parallel Hybrid Testing Techniques for the Dual-Programming Models-Based Programs

The importance of high-performance computing is increasing, and Exascale systems will be feasible in a few years. These systems can be achieved by enhancing the hardware’s ability as well as the parallelism in the application by integrating more than one programming model. One of the dual-programming model combinations is Message Passing Interface (MPI) + OpenACC, which has several features including increased system parallelism, support for different platforms with more performance, better productivity, and less programming effort. Several testing tools target parallel applications built by using programming models, but more effort is needed, especially for high-level Graphics Processing Unit (GPU)-related programming models. Owing to the integration of different programming models, errors will be more frequent and unpredictable. Testing techniques are required to detect these errors, especially runtime errors resulting from the integration of MPI and OpenACC; studying their behavior is also important, especially some OpenACC runtime errors that cannot be detected by any compiler. In this paper, we enhance the capabilities of ACC_TEST to test the programs built by using the dual-programming models MPI + OpenACC and detect their related errors. Our tool integrated both static and dynamic testing techniques to create ACC_TEST and allowed us to benefit from the advantages of both techniques reducing overheads, enhancing system execution time, and covering a wide range of errors. Finally, ACC_TEST is a parallel testing tool that creates testing threads based on the number of application threads for detecting runtime errors.

A novel technique for dynamic shear testing of bulk metals with application to 304 austenitic stainless steel

This paper describes a new single-shear specimen (SSS) and method to characterize the dynamic shear behavior of bulk metals using a traditional Split Hopkinson Pressure Bar (SHPB). By this method, the shear behavior of materials can be tested conveniently over a wide range of strain rates within 105 s−1. This technique was applied to a 304 austenitic stainless steel (ASS) under shear strain rates from 0.001 s−1 to 38700 s−1 at room temperature. Based on finite element (FE) simulations, it was found that the deformation of the specimen shear zone was dominated by shear stress/strain components. Stress state parameters represented by stress triaxiality η and Lode angle parameter θ- were found very close to zero, indicating a deformation mode of simple shear. Besides, an obvious gap existed between the local deformation behavior in the specimen shear zone and the macroscopic stress-strain relations measured by the strain gauges on the SHPB bars. A correction coefficient method was adopted to extract the real shear behavior from the experimentally obtained force-displacement data. Through comparisons between the tested and simulated stress-strain curves, a good agreement was obtained.

Definition of a Simplified Design Procedure of Seismic Isolation Systems for Bridges

In the recent past, numerical and experimental investigations on full-scale isolators have led to extensive improvements in seismic isolation techniques for bridge structures. Significant advances in dynamic testing techniques have been made at both software and hardware levels, and the response of an isolated bridge can be realistically simulated. In general, the response of an isolated bridge structure is strongly affected by the valley topography; therefore, high piers may not need isolation devices, since they are flexible enough to accommodate the design displacement in the elastic range. On the other hand, at those locations no hysteretic damping is provided and higher displacements can be achieved, compared to the maximum displacement allowance. In this work, a simplified procedure is proposed for the optimization of isolation systems for bridge structures. The seismic response of a designed case study structure is investigated through nonlinear time history analyses, and the effective contributions of both the nonlinear hysteretic behaviour of isolators and the elastic response of piers are considered. Regarding displacement and force responses in particular, the results show a very good agreement between mean and single-event peak responses, and the corresponding values returned by the proposed design procedure.

ACC_TEST: Hybrid Testing Techniques for MPI-Based Programs

Recently, MPI has become widely used in many scientific applications, including different non-computer science fields, for parallelizing their applications. An MPI programming model is used for supporting parallelism in several programming languages, including C, C++, and Fortran. MPI also supports integration with some programming models and has several implementations from different vendors, including open-source and commercial implementations. However, testing parallel programs is a difficult task, especially when using programming models with different behaviours and types of error based on the programming model type. In addition, the increased use of these programming models by non-computer science specialists can cause several errors due to lack of experience in programming, which needs to be considered when using any testing tools. We noticed that dynamic testing techniques have been used for testing the majority of MPI programs. The dynamic testing techniques detect errors by analyzing the source code during runtime, which will cause overheads, and this will affect the program's performance, especially when targeting massive parallel applications generating thousands or millions of threads. In this paper, we enhance ACC_TEST to have the ability to test MPI-based programs and detect runtime errors occurring with different types of MPI communications. We decided to use hybrid-testing techniques by combining both static and dynamic testing techniques to gain the benefit of each and reduce the cost.

Multi-hazard real-time hybrid simulation of a tall building with damped outriggers

The essence of real-time hybrid simulation (RTHS) is its ability to combine the benefits of physical testing and computational simulations and thereby efficiently simulate the dynamic response of a structure. The method is known to be accurate and more affordable compared to other dynamic testing techniques. However, the RTHS technique has primarily been applied to simulate seismic effects in structures. This paper successfully extends its application to wind response simulation of a 40-storey tall building outfitted with nonlinear fluid viscous dampers. In the RTHS, the building frame is modelled numerically, and the dampers are modelled physically. A series of RTHS is performed for both seismic and wind loadings. This paper presents the RTHS implementation procedure for multiple hazards, discusses the RTHS results and summarises the issues and challenges regarding the current implementation. The paper concludes with some remarks on the essence of RTHS in performance-based engineering considering multiple hazards.

A Full‐Scale Experimental Study of the Vertical Dynamic and Static Behavior of the Pier‐Cap‐Pile System

The bearing capacity evaluation of bridge substructures is difficult as the static loading test (SLT) cannot be employed for the bridges in services. As a type of dynamic nondestructive test technique, the dynamic transient response method (TRM) could be employed to estimate the vertical bearing capacity when the relationship between static stiffness and dynamic stiffness is known. The TRM is usually employed to evaluate single piles. For the pier‐cap‐pile system, its applicability should be investigated. In the present study, a novel full‐scale experimental study, including both TRM test and SLT, was performed on an abandoned bridge pier with grouped pile foundation. The test included three steps: firstly, testing the intact pier‐cap‐pile system; then, cutting off the pier and testing the cap‐pile system; finally, cutting off the cap and testing the single pile. The TRM test was repeatedly performed in the above three steps, whereas the SLT was only performed on the cap‐pile system. Based on the experimental results, the ratio of dynamic and static stiffness of the cap‐pile system was obtained. The results show that (1) in the low‐frequency range (between 10 and 30 Hz in this study), the dynamic stiffness of the whole system is approximately four times of that of a single pile; (2) the ratio of dynamic and static stiffness of the cap‐pile system tested in the study is approximately 1.74, which was similar to other tested values of a single pile; (3) to evaluate the capacity of similar cap‐pile system and with similar soil layer conditions by TRM, the value of Kd/Ks tested in the study can be used as a reference.

Dynamic Random Testing of Web Services: A Methodology and Evaluation

In recent years, service oriented architecture (SOA) has been increasingly adopted to develop distributed applications in the context of the Internet. To develop reliable SOA-based applications, an important issue is how to ensure the quality of web services. In this article, we propose a dynamic random testing (DRT) technique for web services, which is an improvement over the widely-practiced random testing (RT) and partition testing (PT) approaches. We examine key issues when adapting DRT to the context of SOA, including a framework, guidelines for parameter settings, and a prototype for such an adaptation. Empirical studies are reported where DRT is used to test three real-life web services, and mutation analysis is employed to measure the effectiveness. Our experimental results show that, compared with the three baseline techniques, RT, Adaptive Testing (AT) and Random Partition Testing (RPT), DRT demonstrates higher fault-detection effectiveness with a lower test case selection overhead. Furthermore, the theoretical guidelines of parameter setting for DRT are confirmed to be effective. The proposed DRT and the prototype provide an effective and efficient approach for testing web services.

ART4SQLi: The ART of SQL Injection Vulnerability Discovery

SQL injection (SQLi) is one of the chief threats to the security of database-driven Web applications. It can cause serious security issues such as authentication bypassing, privacy leakage, and arbitrary code execution. Dynamic testing techniques are used in SQLi vulnerability discovery, which de-facto approach is to maintain a collection of elaborately designed user inputs (aka. attack payloads) and based on it to compose malicious SQL queries to Web applications. Such techniques are effective to reveal SQLi threats before an application is released, thus reducing the cost of manual analysis, monitoring or postdeployment of other defensive mechanisms. However, because of the diversity of SQLi attacks and the difficulty of SQLi discovery, the process to execute payloads can be costly, time-consuming, and even risky. In this paper, we approach from a test case prioritization perspective to give a more effective SQLi discovery proposal, which is based on adaptive random testing with the aim to successfully trigger an SQLi within limited attempts. To evaluate our method, we conduct an experiment using three extensively adopted open source vulnerable benchmarks. The experiment results indicate that our method ART4SQLi can effectively improve the conventional random testing approach on three common benchmarks by more than 26% in reducing the number of SQLi attempts before accomplishing a successful injection.

Dynamic Testing Technique Based on Multi-channel Photonic Doppler Velocimetry for Investigating the Dynamic Behavior of Materials

In the present paper, more attention is paid to develop a new optical measurement approach of split-Hopkinson pressure bar (SHPB) and wave propagation inverse analysis (WPIA) by using multi-channel photonic Doppler velocimetry (PDV). Based on the particle velocities measured by PDV, the dynamic stress–strain curve of material is obtained in SHPB tests. The strain is determined by the radial particle velocity of specimen, and the stress is determined by the free surface particle velocity of the transmitted bar. The results obtained by the new method coincide with those obtained by the conventional strain gauge measurements. The new method is non-intrusive and insensitive to electrical noise, making it significantly more reliable than strain gauges. Using the oblique incidence of laser beam, a series of particle velocity wave propagation signals for long rod specimen are measured simultaneously. Based on the measurements of particle velocity profile, the dynamic constitutive response of polymethyl methacrylate (PMMA) is determined by WPIA method. The comparison between the dynamic stress–strain curve and the quasi-static one indicates that the strain-rate effect must be taken into account for PMMA.

System Identification Guidance for Multirotor Aircraft: Dynamic Scaling and Test Techniques

State-space system identification was performed to extract flight dynamic models for hovering flight of a 55 cm, 1.56 kg hexacopter unmanned aerial vehicle. Different input excitation techniques were tested to determine which maneuvers provided high-quality system identification results for small-scale multirotor vehicles. These input excitation techniques included automated frequency sweeps, varying in amplitude, and multisine sweeps. Coherence, Cramer–Rao bounds, and insensitivities were used as metrics for comparing the system identification results. A parametric variation of frequency sweep amplitudes were performed in all axes (roll, yaw, pitch, and heave) to provide guidance on frequency sweep amplitude for small-scale multirotor unmanned aerial systems. The dynamics of the 55 cm hexacopter were used to estimate the dynamics of a larger 127-cm hexacopter via Froude scaling based on hub-to-hub distance as the characteristic length. The scaled results were compared to an actual system identification model of a 127-cm hexacopter.

Real-time aerodynamics hybrid simulation: Wind-induced effects on a reduced-scale building equipped with full-scale dampers

As buildings are designed to be taller and more slender, they become lighter and more flexible with less inherent damping. If left uncontrolled, excessive wind-induced building response can cause serious safety and serviceability issues. Additional damping provided by adding an auxiliary damping system to the tall building is considered as one of the most cost-effective means to suppress the wind-induced response. Typically, the performance of these damping systems is evaluated experimentally with scaled damper and building models. However, the simplified small-scale dampers may not truly reflect the complex behavior of the full-scale damping systems. To realize the effective reduction of the wind-induced response of tall buildings, a real-time aerodynamics hybrid simulation (RTAHS) methodology that can offer improved response evaluation of a tall building integrated with an auxiliary damping system is introduced in this study. In this novel dynamic testing approach, the accurate evaluation of wind-induced tall building response is achieved by interacting an aeroelastic model of the tall building with the numerical model of the full-scale damper via interfacing actuators during the wind-tunnel tests. The feasibility and simulation accuracy of the proposed dynamic testing technique in the wind tunnel is numerically demonstrated by two case studies involving the wind-induced response reduction of a tall building equipped with both small-scale and full-scale damper properties.

Underwater explosions in dynamic testing of hydraulic structures

A technique for dynamic field testing of hydraulic structures for stability against the shock wave generated by an underwater explosion is described. The choice of the shock wave parameters, the charge mass, and the distance from the epicenter to the structure is justified. A method to determine the dynamic response of the structure is outlined. The dynamic characteristics of a concrete dam are estimated, and the damping factors and natural frequencies of the structure are specified.

A summary of defect evolution and health monitoring of wind turbine blades

The wind turbine blade is one of most critical systems in terms of failure as the wind turbines are rapidly becoming larger and more complicated. Developing better design procedures are ongoing and the enhancements over the time are promising and requires reliable supportive monitoring and maintenance systems to ensure the satisfactory level of asset cost effectiveness. The purpose of the paper is to review the contributions concerning the wind turbine blade defects, in order to: understand how the defects in wind turbine blades evolve, i.e., initiate and propagate over the lifetime and to understand how the defects in wind turbine blades can be monitored. The paper reviews the mechanical dynamic models, testing and condition monitoring techniques. The paper proceeds to provide a generic defect evolution scenario with aim to enhance the fragmented understanding of the micro and macro-structure behaviour of the wind turbine blades.

Road Network Resilience: How to Identify Critical Links Subject to Day-to-Day Disruptions

Disruptive events occur on road networks on a daily basis and affect traffic flow. Resilience analysis aims to assess the consequences of such disruptions by quantifying the ability of a network to absorb and react to adverse events. In this paper, we advance a methodological approach based on resilience stress testing and a dynamic mesoscopic simulator. We aim to identify and rank the links most critical to the overall performance of the road network, taking into account the dynamic properties of road traffic and focusing on day-to-day disruptions. As a metric to quantify road network performance in the presence of such disruptions, we use the increase in overall travel cost. We then compare our approach with purely topological approaches. We discuss the advantages and drawbacks of the different analyzed metrics. We prove that link ranking varies greatly depending on the metric. Specifically, the proposed stress testing methodology can produce very accurate results by taking into account demand and congestion, but requires computationally intensive simulations, being therefore prohibitive even on medium-sized networks. Conversely, purely static topological metrics can be inaccurate if they do not take into account traffic demand and network dynamics. Our study highlights the need for joining traditional traffic-agnostic topological resilience analysis with demand-aware dynamic stress testing techniques.

RESEARCH ON DYNAMIC TEST TECHNOLOGY FOR WIND TURBINE BLADE AIRFOIL

The dynamic oscillation process of wind turbine blades is usually accompanied by pitching and yaw. Due to the unclear understanding of many dynamic problems previously, a safer design is adopted at the expense of increasing the weight of the blade structure in engineering, usually neglecting the influence of the yaw oscillation. The design of large wind turbines has put forward higher requirements for obtaining more comprehensive and accurate dynamic loads of airfoils. It is of great significance to study the influence of yaw oscillation on the dynamic aerodynamic characteristics of airfoil. In view of this, the dynamic wind tunnel test on yaw oscillation of airfoil is carried out in this paper for the first time. The “electronic cam” technology is used instead of the mechanical cam to realize the stepless adjustment of oscillation frequency and oscillation angle. Based on the designed electronic external trigger device, the real-time measurement of the dynamic flow field is realized. Meanwhile, the synchronous acquisition of wind tunnel flow, model angular displacement and dynamic pressure data is realized. Furthermore, the static pressure measurement, pitching / yaw dynamic pressure measurement, PIV and fluorescent wire test are carried out respectively. The accuracy of the test results is high, and the regular pattern is reasonable. Besides, the influence mechanism of wall interference in dynamic test is analyzed. Research shows that: there is also obvious hysteresis effect on the dynamic aerodynamic parameters of yaw oscillation airfoil with the changing of the angle of attack. And with the increase of oscillation frequency, the aerodynamic hysteresis characteristics of the airfoil under pitching and yaw oscillation are all enhanced. The dynamic stall vortex at the positive stroke is delayed due to the pitching oscillation. The pressure distribution of the airfoil is greatly influenced by the strong three-dimensional effect at the intersection of the wind tunnel wall and the model tip. Overall, the dynamic test technique of yaw oscillation established in this paper can provide technical support for the study of the dynamic swept effect of the wind turbines.

A novel evaluation strategy for fatigue reliability of flexible nanoscale films

In order to evaluate fatigue reliability of nanoscale metal films on flexible substrates, here we proposed an effective evaluation way to obtain critical fatigue cracking strain based on the direct observation of fatigue damage sites through conventional dynamic bending testing technique. By this method, fatigue properties and damage behaviors of 930 nm-thick Au films and 600 nm-thick Mo-W multilayers with individual layer thickness 100 nm on flexible polyimide substrates were investigated. Coffin-Manson relationship between the fatigue life and the applied strain range was obtained for the Au films and Mo-W multilayers. The characterization of fatigue damage behaviors verifies the feasibility of this method, which seems easier and more effective comparing with the other testing methods.

Use of the Kolsky method for dynamic tests of brittle media

The dynamic test techniques used to obtain the mechanical properties of brittle materials are described. The techniques are based on the fundamental Kolsky method using the Split-Hopkinson Pressure Bar. Dynamic tests are characterized by high intensity and short duration and the influence of inertia on their results should be ruled out which is especially important for brittle media. The prerequisites and assumptions presented methods are described to justify the validity of the obtained data. The methods allow to obtain dynamic deformation diagrams at compression, splitting, indirect tension, shear and triaxial stress state and also to determine the ultimate strength, strain and time properties of brittle materials. The techniques are approved in the tests of ceramic bricks, finegrain concrete and fiber-reinforced concrete.

Model-based framework for multi-axial real-time hybrid simulation testing

Real-time hybrid simulation is an efficient and cost-effective dynamic testing technique for performance evaluation of structural systems subjected to earthquake loading with rate-dependent behavior. A loading assembly with multiple actuators is required to impose realistic boundary conditions on physical specimens. However, such a testing system is expected to exhibit significant dynamic coupling of the actuators and suffer from time lags that are associated with the dynamics of the servo-hydraulic system, as well as control-structure interaction (CSI). One approach to reducing experimental errors considers a multi-input, multi-output (MIMO) controller design, yielding accurate reference tracking and noise rejection. In this paper, a framework for multi-axial real-time hybrid simulation (maRTHS) testing is presented. The methodology employs a real-time feedback-feedforward controller for multiple actuators commanded in Cartesian coordinates. Kinematic transformations between actuator space and Cartesian space are derived for all six-degrees-offreedom of the moving platform. Then, a frequency domain identification technique is used to develop an accurate MIMO transfer function of the system. Further, a Cartesian-domain model-based feedforward-feedback controller is implemented for time lag compensation and to increase the robustness of the reference tracking for given model uncertainty. The framework is implemented using the 1/5th-scale Load and Boundary Condition Box (LBCB) located at the University of Illinois at Urbana- Champaign. To demonstrate the efficacy of the proposed methodology, a single-story frame subjected to earthquake loading is tested. One of the columns in the frame is represented physically in the laboratory as a cantilevered steel column. For realtime execution, the numerical substructure, kinematic transformations, and controllers are implemented on a digital signal processor. Results show excellent performance of the maRTHS framework when six-degrees-of-freedom are controlled at the interface between substructures.

Brittle materials at high-loading rates: an open area of research.

Brittle materials are extensively used in many civil and military applications involving high-strain-rate loadings such as: blasting or percussive drilling of rocks, ballistic impact against ceramic armour or transparent windshields, plastic explosives used to damage or destroy concrete structures, soft or hard impacts against concrete structures and so on. With all of these applications, brittle materials are subjected to intense loadings characterized by medium to extremely high strain rates (few tens to several tens of thousands per second) leading to extreme and/or specific damage modes such as multiple fragmentation, dynamic cracking, pore collapse, shearing, mode II fracturing and/or microplasticity mechanisms in the material. Additionally, brittle materials exhibit complex features such as a strong strain-rate sensitivity and confining pressure sensitivity that justify expending greater research efforts to understand these complex features. Currently, the most popular dynamic testing techniques used for this are based on the use of split Hopkinson pressure bar methodologies and/or plate-impact testing methods. However, these methods do have some critical limitations and drawbacks when used to investigate the behaviour of brittle materials at high loading rates. The present theme issue of Philosophical Transactions A provides an overview of the latest experimental methods and numerical tools that are currently being developed to investigate the behaviour of brittle materials at high loading rates.This article is part of the themed issue 'Experimental testing and modelling of brittle materials at high strain rates'.

Dynamic and atomic-scale understanding of the twin thickness effect on dislocation nucleation and propagation activities by in situ bending of Ni nanowires

Although their mechanical behavior has been extensively studied, the atomic-scale deformation mechanisms of metallic nanowires (NWs) with growth twins are not completely understood. Using our own atomic-scale and dynamic mechanical testing techniques, bending experiments were conducted on single-crystalline and twin-structural Ni NWs (D=∼40nm) using a high-resolution transmission electron microscope (HRTEM). Atomic-scale and time-resolved dislocation nucleation and propagation activities were captured in situ. A large number of in situ HRTEM observations indicated strong effects from the twin thickness (TT) on dislocation type and glide system. In thick twin lamella (TT>∼12nm) and single-crystalline NWs, the plasticity was controlled by full dislocation nucleation. For NWs with twin thicknesses of ∼9nm<TT<∼12nm, full and partial dislocation nucleation occurred from the free surface, and the dislocations glided on multiple systems and interacted with each other during plastic deformation. For NWs with twin thicknesses of ∼6nm<TT<∼9nm, partial dislocation nucleation from the free surface and the gliding of those dislocations on the plane that intersected the twin boundaries (TBs) were the dominant plasticity events. For the NWs with twin thicknesses of ∼1nm<TT<∼6nm, the plasticity was accommodated by a partial dislocation nucleation process and glide parallel to the TBs. When TT<∼1nm, TB migration and detwinning processes resulting from partial dislocation nucleation and glide adjacent to the TBs were frequently observed.