The Sustainable Livelihoods Approach as an impact assessment tool for development interventions in rural Tigray, Ethiopia : opportunities & challenges

Measuring the impact and sustainability of development programmes requires the development of appropriate assessment tools. This paper examines the Sustainable Livelihoods Approach's (SLA) potential to be transformed to and called in as a practical instrument to evaluate the impact of development interventions in rural Tigray (Northern Ethiopia). Fieldwork has been carried out in communities in woreda Dogua Tembien using participant observation and open interviews as methods. Next to more general challenges of defining, measuring and comparing livelihood assets, context specific factors complicate the operationalisation of the SLA as an impact assessment tool in the area. The SLA distinguishes between livelihood assets on the one hand and transforming structures and processes on the other. The latter lend meaning and value to the former. This conceptual distinction is worthy as it makes the two-way interaction between both categories explicit and escapes from reducing institutions, organisations, policies and legislation to context or background. However, in practice the boundaries are fuzzy and not easy to interpret. The example of religion as a cross-cutting organizing principle illustrates this assumption. Moreover the distinction complicates the operationalisation of the SLA as it implies the meaning and value of capitals to be volatile and depending on the prevailing social, institutional and organisational environment. This is exemplified with the big transforming power of policy shifts in the area. For the SLA to serve as an impact assessment tool, it requires a culture- and policy-sensitive analysis of farmers' asset base. Only a sound understanding of the interactions between livelihood assets and transforming structures and processes can lead to a locally contextualised, meaningful and workable impact assessment tool that measures asset levels using indicators that reflect farmers' own criteria to judge development interventions

Frequency-phase modulated thermal wave radar : stepping beyond state-of-the-art infrared thermography

Thermal wave radar is a state-of-the-art non-destructive testing method inspired by radio wave radar systems. The underlying principle of the technique is the application of a modulated excitation waveform by which the total energy of the response signal can be compressed in time-domain through cross-correlation. This leads to an enhanced depth resolution and increased signal to noise ratio in optical infrared thermography. Frequency sweep and Barker binary phase modulation are the two popular and widely researched excitation waveforms of the technique. In this research, a novel frequency-phase modulated waveform is introduced, which is designed for optimized performance of thermal wave radar

Backside delamination detection in composites through local defect resonance induced nonlinear source behavior

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Multi-scale gapped smoothing algorithm for robust baseline-free damage detection in optical infrared thermography

Flash thermography is a promising technique to perform rapid non-destructive testing of composite materials. However, it is well known that several difficulties are inherently paired with this approach, such as non-uniform heating, measurement noise and lateral heat diffusion effects. Hence, advanced signal-processing techniques are indispensable in order to analyze the recorded dataset. One such processing technique is Gapped Smoothing Algorithm, which predicts a gapped pixel’s value in its sound state from a measurement in the defected state by evaluating only its neighboring pixels. However, the standard Gapped Smoothing Algorithm uses a fixed spatial gap size, which induces issues to detect variable defect sizes in a noisy dataset. In this paper, a Multi-Scale Gapped Smoothing Algorithm (MSGSA) is introduced as a baseline-free image processing technique and an extension to the standard Gapped Smoothing Algorithm. The MSGSA makes use of the evaluation of a wide range of spatial gap sizes so that defects of highly different dimensions are identified. Moreover, it is shown that a weighted combination of all assessed spatial gap sizes significantly improves the detectability of defects and results in an (almost) zero-reference background. The technique thus effectively suppresses the measurement noise and excitation non-uniformity. The efficiency of the MSGSA technique is evaluated and confirmed through numerical simulation and an experimental procedure of flash thermography on carbon fiber reinforced polymers with various defect sizes

Investigation to local defect resonance for non-destructive testing of composites

Local defect resonance (LDR) makes use of high frequency vibrations to get a localized resonant activation of a defective region. In this study, the LDR behavior of carbon fiber reinforced polymer (CFRP) coupons with three different types of damages is investigated using broadband measurements obtained with a scanning laser Doppler vibrometer (SLDV). First, the LDR response of flat bottom holes of different depths and sizes is evaluated using a signal-to-noise ratio. Next, results are obtained for ETFE inserts where the difference between (artificial) delaminations and inserts is outlined. At last, the vibrational response of a CFRP coupon with barely visible impact damage is investigated. This type of damage has a more complex structure, and it is shown that frequency band data (an alternative to the single frequency LDR) performs well in identifying such complex damage

Flash thermography of composites : evaluation of advanced post-processing approaches

Carbon fiber reinforced polymers (CFRP) are composite materials that offer a high stiffness-to-weight ratio in comparison to traditional metals, which explains their increasing use in many high-end applications (e.g. aerospace). However, composites are prone to internal damage that may deteriorate the structural integrity, and thus require reliable and non-destructive testing (NDT) approaches. Infrared thermography (IRT) is a promising NDT technique which provides fast, full-field measurements, and in which hidden defects are detectable based on their thermal signatures. In flash thermography (FT), which is the thermographic technique of interest for this contribution, the component’s surface temperature is rapidly elevated through the application of an intense optical flash. Subsequent recording of the cooling down of the stimulated surface, by means of a high-end infrared camera, allows to detect defects by searching for anomalies in the surface temperature (due to heat build-up above the defect). Considering the anisotropic diffusivity and high damping of thermal waves in CFRP, advanced post-processing techniques are indispensable to detect deep defects (> 2 mm in CFRP). In this paper, FT is performed on several CFRPs with various defects (flat bottom holes, Teflon inserts and barely visible impact damage). This thermographic dataset is then analyzed using various post-processing techniques, including pulsed phase thermography (PPT), principal component thermography (PCT), thermographic signal reconstruction (TSR) and dynamic thermal tomography (DTT), in order to improve the defect detectability and assessment. The performance of the employed processing techniques is critically evaluated

Enhanced detectability of barely visible impact damage in CFRPs : vibrothermography of in-plane local defect resonances

This paper demonstrates the enhanced detectability of barely visible impact damage in CFRPs through low power vibrothermography of in-plane local defect resonances (LDR). In-plane LDR (LDRxy), with a higher cut-off frequency than out-of-plane LDR (LDRz), generally enhances the rubbing interaction and viscoelastic damping of defects and leads to higher vibration-induced heating. The most prominent LDRz and LDRxy frequencies of an impacted CFRP are extracted from its vibrational spectra under a broadband sweep excitation, measured by a 3D infrared laser Doppler vibrometer. The sample is then inspected through lock-in vibrothermography at the extracted LDR frequencies and the distintively higher detectability of LDRxy compared to LDRz is evidenced. Moreover, it is observed that the thermal contrast induced by LDRxy is so high, that it allows for easy detection of impact damage by live monitoring of infrared thermal images during a single broadband sweep vibration excitation

An experimental study on the defect detectability of time- and frequency-domain analyses for flash thermography

A defect's detectability in flash thermography is highly dependent on the applied post-processing methodology. The majority of the existing analysis techniques operate either on the time-temperature data or on the frequency-phase data. In this paper, we compare the efficiency of time- and frequency-domain analysis techniques in flash thermography for obtaining good defect detectability. Both single-bin and integrated-bin evaluation procedures are considered: dynamic thermal tomography and thermal signal area for the time-domain approach, and frequency domain tomography and adaptive spectral band integration for the frequency-domain approach. The techniques are applied on various carbon fiber reinforced polymer samples having a range of defect sizes and defect types. The advantages and drawbacks of the different post-processing techniques are evaluated and discussed. The best defect detectability is achieved using the integrated procedure in frequency domain