Destructive testing | EPFL Graph Search

In destructive testing (or destructive physical analysis, DPA) tests are carried out to the specimen's failure, in order to understand a specimen's performance or material behavior under different loads. These tests are generally much easier to carry out, yield more information, and are easier to interpret than nondestructive testing. Applications Destructive testing is most suitable, and economic, for objects which will be mass-produced, as the cost of destroying a small number of specimens is negligible. It is usually not economical to do destructive testing where only one or very few items are to be produced (for example, in the case of a building). Analyzing and documenting destructive failure mode Analyzing and documenting the destructive failure mode is often accomplished using a high-speed camera recording continuously (movie-loop) until the failure is detected. Detecting the failure can be accomplished using a sound detector or stress gauge which produce

New Reliability Assessment of MEMS Components under Accumulative Testing for Space Applications

Maxime Auchlin

This dissertation proposes a novel accumulative test method for MEMS-based, commercial off-the-shelves inertial measure units (IMUs) from the automotive field. The need for clarification and augmentation of the corpus of knowledge on MEMS reliability for space applications is addressed. Faster and less tedious test procedures, better understanding of the failure modes as well as the possible prediction models and numerical simulations are at the center of a pragmatic vision that shall keep the industrial end-user and applications in sight. The IMU is used in several sequential accumulative test campaigns under various environments. The device comprises notably of a X,Y-axis accelerometer. The structure of this research is elaborated following an increasing level of complexity, culminating at a seven-step stress test, alternating between thermal shocks and vibration testing, followed by thorough failure modes and effects analysis of the failed or degraded devices.Chapter 1 describes the world of MEMS. Highlights of uses in space technologies are presented, as well as the state-of-the art of reliability testing and corresponding failure mechanisms. Remaining open questions about accumula-tive testing are covered.Chapter 2 elaborates on the stakeholders implied in this research. It is important to keep in mind the highly applic-ative and industrially oriented vocation of reliability testing. Choice of the IMU for the various test campaigns is done. A thorough destructive physical analysis has been performed to gain knowledge of the devices' construction.Chapter 3 details the experimental method. Functional tests were performed before, in-between, and after a test step on the devices alone (no peripheral circuitry). Testing methodology description follows with the development of a mono-parameter, two-step stress test procedure. Such procedure fails to properly assess the reliability of the robust MEMS components, even with harsher environments than commonly used standards (MIL-STD-883). Accu-mulative testing was therefore performed. Chapter 4 reports the experimental results from the different test campaigns: (i) temperature cycling followed by vibration, (ii) thermal shocks followed by vibration, (iii) vibration and thermal shocks alternated in a seven-step sequence. The first campaign yielded to the failure of the devices due to die attach weakening, while the two oth-ers showed intense degradation without failing. X-ray tomography was used to identify failure modes, as well as high-resolution X-ray diffraction for residual stress identification in the silicon dies. Other complementary tests were performed (die shear, wire bonds pull).In Chapter 5, a finite element model of the MEMS device is designed. A thermal-only model allows to verify that devices are at thermal equilibrium during testing. Then, by relying on a viscoelastic, stress and strain data can be obtained over a thermal cycle for the die attach. The found values suggest that accumulation of plastic damages are very likely to occur due to the build-up of thermal stress in the adhesive: a result corroborated by the experi-mental observations.By proposing a novel approach to robust MEMS reliability approach and diving deep into the failure modes and effects of accumulative testing, this research aims at contributing to the elaboration of the next framework that will help the space community to foster a wider use of COTS devices in space applications.

EPFL2021

Addressing the need to monitor concrete fatigue with Non Destructive Testing: results of Infrastar European project

Antoine Bassil, Imane Bayane, Eugen Brühwiler, Xiao Wang

Fatigue is one of the most prevalent issues, which directly influences the service life expectancy of concrete structures. Fatigue has been investigated for years for steel structures. However, recent findings suggest that concrete structures may also be significantly subjected to fatigue phenomena that could lead to premature failure of certain structural elements. To date, fatigue of reinforced concrete has been given little focus. Knowledge on the influence factors and durability/capacity effects on this material should be improved. Current technological means to measure fatigue in civil structures like bridges and wind turbines (both onshore and offshore) are outdated, imprecise and inappropriate. Meanwhile, this topic has got much more attention as time-variant loading on concrete structures plays an increasing role, e.g. in bridges with increasing traffic and heavier trucks, and for wind turbines for renewable energy production, e.g. for offshore wind turbine support structures affected by wind and waves. The European Innovative Training Networks (ITN) Marie Skłodowska-Curie Actions project INFRASTAR (Innovation and Networking for Fatigue and Reliability Analysis of Structures - Training for Assessment of Risk) provides research training for 12 PhD students. The project aims to improve knowledge for optimizing the design of new structures as well as for more realistic verification of structural safety and more accurate prediction of the remaining fatigue lifetime of existing concrete structures. First, the INFRASTAR research framework is detailed. Then it will be exemplified through the presentation of the major results of the four PhD students involved in the work package dealing with auscultation and monitoring. This includes the development and improvement of Fiber Optics (FO) and Coda Wave Interferometry (CWI) for crack sizing and imagery, new sensor technologies and integration, information management, monitoring strategy for fatigue damage investigation and lifetime prediction.

2018

Probing the buckling of pressurized spherical shells

Arefeh Abbasi, Pedro Miguel Nunes Pereira de Almeida Reis, Dong Yan

The prediction of the critical buckling conditions of shell structures is plagued by imperfection sensitivity. Non-destructive testing through point-load probing has been recently proposed to map the stability landscape of cylindrical shells. However, the counterpart procedure for spherical shells is still debatable. Here, we focus on the mechanical response of pressurized spherical shells containing a single dimple–like defect to a point probe. Combining experiments, finite element modeling, and existing results from classic shell theory, we characterize the nonlinear force-indentation response of imperfect shells at different pressurization levels. From these curves, we seek to identify the critical buckling pressure of the shell. In particular, the indentation angle is varied systematically to examine its effect on the probing efficacy. We find that the critical buckling point can be inferred non-destructively by tracking the maxima of the indentation force–displacement curves, if the probe is implemented sufficiently close to the defect. When probing further away from the defect, the test fails in predicting the onset of buckling since the deformation due to indentation remains localized in the vicinity of the probe. Using FEM simulations and shallow shell theory, we quantify the characteristic length associated with this localized deformation, both in the linear and nonlinear regimes. Our results demonstrate the limiting conditions of applicability for the usage of probing as a non-destructive technique to assess the stability of spherical shells.