New ECMA 74 operating conditions for personal computers and workstations

Annex C in ECMA 74 outlines the operating conditions for personal computers and workstations during acoustic testing. In practice, the way systems are used and designed changes over time. After InterNoise 2018 in Chicago, a special IT industry workgroup was formed with the goal to update this section in Annex C to better reflect current workloads during use. This paper outlines the new operating conditions that were developed by this workgroup. It describes the different operating modes to be measured, and how to set and document power and performance parameters during the acoustic measurements. In addition to the standard idle condition, it includes operating conditions selected from the following usage scenarios: 1) web browsing, 2) office productivity, 3) media content creation, and 4) power user/gaming.

Evaluation of Nonuniformity of Elastic Properties of Sheets Made from Closed-Сell Polyolefin Foams by Acoustic Method

The widespread use of polyolefin foams in strategically important industries is due to their high thermal, sound and vibration insulation properties. The aim of the work was to evaluate the non-uniformity of elastic properties over the area of sheets of polyolefin foams of various types using the acoustic non-contact shadow amplitude method of testing and confirmation by the structural analysis method.The article presents the developed installation and a new method of non-contact acoustic testing of sheets made of closed-cell polyolefin foams based on recording the amplitude of the pulse that passed through the sheet and allowing to assess to the unevenness of its elastic properties during scanning. Studies of uneven elastic properties were carried out on sheets of closed-cell polyolefin foams of the ISOLON 500 and ISOLON 300 brands which differ in material and manufacturing technology (technique of cross-linking, method and multiplicity of foaming).It is shown that the absolute amplitude of the signal and its spread relative to the average value is affected by the structure of the foam polyolefin material and its heterogeneity over the area of the studied sheet determined by the production technology which is confirmed visually using microscopy.Studies have shown the effect on the indications unevenness of the method of obtaining and the apparent density of the material. It is shown that the most uneven elastic properties and structure belong to sheets of polyolefin foam obtained by chemical cross-linking technology (the unevenness of Δ was 6.5 %). Among the physically cross-linked sheets of polyolefin foam the most uniform in structure and elastic properties are samples made of ethylene vinyl acetate with Δ = 3.8 %, as well as sheets with a high foaming rate (Δ = 3.9 %). The unevenness of structure of the studied sheets of polyolefin foams was confirmed by optical microscopy of sections in two mutually perpendicular directions.

Damage Characterisation in Composite Laminates Using Vibro-Acoustic Technique

The need to characterise in-service damage in composite structures is increasingly becoming important as composites find higher utilisation in wind turbines, aerospace, automotive, marine, among others. This paper investigates the feasibility of simplifying the conventional acousto-ultrasonic technique set-up for quick and economic one-sided in-service inspection of composite structures. Acousto-ultrasonic technique refers to the approach of using ultrasonic transducer for local excitation while sensing the material response with an acoustic emission sensor. However, this involves transducers with several auxiliaries. The approach proposed herewith, referred to as vibro-acoustic testing, involves a low level of vibration impact excitation and acoustic emission sensing for damage characterisation. To test the robustness of this approach, first, a quasi-static test was carried out to impute low-velocity impact damage on three groups of test samples with different ply stacking sequences. Next, the vibro-acoustic testing was performed on all test samples with the acoustic emission response for the samples acquired. Using the acoustic emission test sample response for all groups, the stress wave factor was determined using the peak voltage stress wave factor method. The stress wave factor results showed an inverse correlation between the level of impact damage and stress wave factor across all the test sample groups. This corresponds with what has been reported in literature for acousto-ultrasonic technique; thus demonstrating the robustness of the proposed vibro-acoustic set-up. Structural health monitoring, impact damage, acousto-ultrasonic testing, non-destructive testing.

CURRENT TRENDS IN DEVELOPMENT OF ACOUSTIC NON-DESTRUCTIVE TESTING METHODS IN AVIATION INDUSTRY (review)

The document includes the below main trends in development of acoustic non-destructive testing methods in aviation industry: automation and enhancement of the sensitivity the testing, development of Procedures for acoustic non-destructive testing methods for products in case of repair and use of products, probabilistic assessment of the outcomes of the ultrasonic non-destructive testing, mathematic simulation of the ultrasonic non-destructive testing, development of the ultrasonic non-destructive testing by applying state-of-the-art technologies, development of the low-frequency acoustic testing methods, development of a Procedure on training of specialists who conduct NDT. The experience of NRC «Kurchatov institute» – VIAM is pointed out to show an example on the implementation of main trends on ultrasonic testing development.

Quick assessment of the potato chip crispness using the mechanical-acoustic measurement method

Traditional assessment method for the food crispness was sensory analysis which was time consuming and needed experienced panelists. Aiming to to develop a quick evaluation of the food crispness, a mechanical-acoustic testing method was proposed where two parameters-maximum force (Fmax) and maximum acoustic energy in unit time (SEmax) were applied to assess the crispness of dried potato chips. It was found the mechanical-acoustic testing was completed in about 1.2 s and the potato chips had a statistic distributions for Fmax and SEmax. The brand A potato chips had a statistic average Fmax of 13.48 N and SEmax of 93.51 mV·ms. Three kinds of potato chips can be effectively differentiated according to the statistic average SEmax and Fmax. Sensory “crispness” had a good correlation with the statistic average SEmax. This work shows that it is feasible for a quick measurement of the food crispness using this mechanical-acoustic method.

Early stage crack detection in mechanically joined steel/aluminum joints by condition monitoring

Monitoring systems for machines, plants, materials and equipment are increasingly used in production processes. These online condition monitoring systems can detect damage or excessive loads at an early stage and can drastically reduce or prevent long downtimes of plants and machines as well as high repair and maintenance costs. This paper depicts a method for online crack detection with pattern recognition methods for specimens joined by self-pierce riveting under cyclic load in fatigue tests (laboratory application). A software specially conceived for this application was developed. This software, AnrissMF, uses active acoustic testing with a structure-borne sensor to detect cracks in the joints at a very early stage. It is shown in this paper that this software can detect cracks much earlier than classical failure criteria for joints (i. e. before any drop in stiffness or frequency is observed). Furthermore, the successful application of software AnrissMF for online crack detection during the fatigue strength test is presented.