Application of micro-tensile test for material characterization of mild steel DC01

During recent years, material characterization based on miniature tensile specimens has been investigated extensively. The Small Punch Test (SPT) is often used for determination of tensile properties but alternative miniature tensile specimen geometries have been suggested due to the limitations of the SPT specimen geometry. However, compared to SPT, the Micro-Tensile Test (M-TT) has a significant advantage since it does not need previous established correlations and enables direct results conversion into standard terms. In this paper, the applicability of the M-TT is investigated for material characterization including Lankford coefficients, hardening laws and stress-strain curves. For this purpose, mild steel DC01 M-TT samples were extracted from sheet in Rolling, Transverse and Diagonal Directions. Moreover, M-TT samples were machined to achieve different thicknesses for indicating thickness effects on strain path

Dynamic compression testing by means of Charpy pendulum

Mathematical modelling and virtual testing of components and structures represent a useful and economic tool for design and safety assessment. The basic mechanical properties which can be found in material standards are not relevant in cases where the real service conditions differ from those applied during standardised testing. Thus e.g. mechanical behaviour at higher strain rates can be interesting for the car components when the simulation of crash situations is used during structure development. The dynamic compression tests are usually performed by means of drop towers, by means of high speed hydraulic testing machines or Hopkinson bar method. At the Mechanical Testing Laboratory of the SKODA Research Inst. in Pilsen, Czech Republic, an instrumentation of Charpy pendulum testing machine was realised in order that it was possible to perform dynamic compression tests [Mentl V., Dzugan J.: Impact compression and tensile testing by means of Charpy pendulum, Int. conf. SUSI 2008 (Structures under Shock and Impact), Algarve, Portugal, 5/2008.], and the compatibility of obtained results in comparison with traditional impact compression tests was verified within the round–robin carried out by TC5 ESIS Sub-Committee on “Mechanical Testing at Intermediate Strain Rates” [Dzugan J., Mentl V.: Compression Round Robin Test Results, ESIS TC5 Meeting, CORUS UK, 2007]. A new striking tup and load measurement system were designed and calibrated. At the same time, a new software was developed which makes it possible to evaluate the test force-deformation record. The goal of this study was 1. to check the possibility of compression testing of high strength materials by means of Charpy pendulum, and 2. to study the strain rate influence on basic mechanical properties

Crack initiation determination for Charpy size specimens

SIGLEAvailable from TIB Hannover: RR 1847(366) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Crack lengths calculation by the unloading compliance technique for Charpy size specimens

The problems with the crack length determination by the unloading compliance method are well known for Charpy size specimens. The final crack lengths calculated for bent specimens do not fulfil ASTM 1820 accuracy requirements. Therefore some investigations have been performed to resolve this problem. In those studies it was considered that the measured compliance should be corrected for various factors, but satisfying results were not obtained. In the presented work the problem was attacked from the other side, the measured specimen compliance was taken as a correct value and what had to be adjusted was the calculation procedure. On the basis of experimentally obtained compliances of bent specimens and optically measured crack lengths the investigation was carried out. Finally, a calculation procedure enabling accurate crack length calculation up to 5 mm of plastic deflection was developed. Applying the new procedure, out of investigated 238 measured crack lengths, more than 80% of the values fulfilled the ASTM 1820 accuracy requirements, while presently used procedure provided only about 30% of valid results. The newly proposed procedure can be also prospectively used in modified form for specimens of a size different than Charpy size. (orig.)Available from TIB Hannover: RR 1847(385) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Thermo-physical properties investigation in relation to deposition orientation for SLM deposited H13 steel

Components produced by additive manufacturing (AM) exhibit a heterogeneous microstructure, hence results in anisotropic mechanical properties. There are very limited studies available on thermo-physical properties variation in relation to the deposition orientation. Variation in these properties may result in an uneven stress distribution. In this work, thermo-physical properties of H13 tool steel fabricated by selective laser melting (SLM) process were experimentally investigated. The effect of three deposition directions (vertical, horizontal and 45 degrees to base plane of build platform) on thermal expansion, thermal diffusivity, specific heat, thermal conductivity and simplified CCT diagram was studied. Additionally, mechanical properties and metallographic studies of the microstructure were carried out together with the porosity evaluation measurements across the specimens

Tensile Property Variation with Wall Thickness in Selective Laser Melted Parts

3D printed parts with complex geometries have different section thickness which leads to non-uniform mechanical properties due to microstructure and defect distributions. Hence, it is essential to characterise the localised mechanical properties to obtain a better understanding of the variability. The tensile property variability is captured by testing miniature sized tensile coupons that are extracted from different part locations which is more representative, when compared to testing printed tensile coupons. In the current work a benchmark study was first carried out to correlate miniature tensile properties with ASTM standard tensile test for different wall thickness in SLM Maraging steels. Following this, tensile property variation at different locations in an AM fabricated impeller part was studied. It was observed the thin sections in the part exhibited large variability in the elongation values. The effect of heat treatment on the tensile properties in the impeller was also studied.Mechanical Engineerin

The Use of Miniature Specimens to Determine Local Properties and Fracture Behavior of LPBF-Processed Inconel 718 in as-Deposited and Post-Treated States

This paper summarizes the assessment of directional anisotropy in local mechanical properties for Laser Powder Bed Fusion (LPBF) IN-718 bulk samples via the use of miniature samples excised from the bulk for both as-deposited and post-treated states. The quasi-static tensile properties at room temperature are investigated at several different locations along the build direction and at different orientations for both considered states. A comparison between the excised miniature tensile specimens and standard-sized sample results have also been conducted and exhibit very good agreement. Significant anisotropy is present in mechanical properties at different build heights for the as-deposited state, while the post-treated material exhibited more homogenous properties, both along the height and for different sampling orientations. However, significant reductions (e.g., >30%) in the strength (Yield, UTS) along with a significant increase in the reduction in area at fracture is found for post-processed materials. Metallography and fractography analyses were conducted in order to begin to determine the source(s) of this anisotropy for the as-deposited state

Mechanical properties characterisation of metallic components produced by additive manufacturing using miniaturised specimens

The various process-specific differences in techniques compared to traditional techniques can produce significantly different mechanical behaviour in additively manufactured (AM) parts compared to traditional bulk counterparts. Components produced by AM are built layer by layer via localised melting. Therefore, both location- and orientation-dependent properties can be expected. Since many AM parts take advantage of the design and topology freedom provided by AM, properties characterisation with the use of standard specimens is not always possible, requiring the use of small-sized specimen techniques. In the current paper, three AM-produced IN-718, Ti-6Al-4V and H13 parts using electron beam powder bed fusion and laser powder bed fusion are evaluated. Local mechanical properties have been assessed with the use of mini-tensile tests that were developed for cases where limited amounts of material are available. The results obtained demonstrate the ability to measure location- and orientation-dependent properties in AM components using such approaches and highlight that additional work by the AM community remains in order to determine the source(s) of such differences

The antimicrobial activity of honey, bee pollen loads and beeswax from Slovakia

The aim of this study was to test the antimicrobial activity of propolis, bee pollen loads and beeswax samples collected in the year 2009 from two locations in Slovakia to pathogenic bacteria, microscopic fungi and yeasts. The antimicrobial effect of the bee product samples were tested using the agar well diffusion method. For extraction, 99.9% and 70% methanol (aqueous, v/v) and 96% and 70% ethanol (aqueous, v/v) were used. Five different strains of bacteria, i.e. Listeria monocytogenes CC M 4699, Pseudomonas aeruginosa CC M 1960; Staphylococcus aureus CC M 3953; Salmonella enterica CC M 4420, Escherichia coli CC M 3988, three different strains of microscopic fungi, Aspergillus fumigatus, Aspergillus flavus, Aspergillus niger, and seven different strains of yeasts Candida krusei, Candida albicans, Candida glabrata, Candida parapsilosis, Candida tropicalis, Geotrichum candidum, Rhodotorula mucilaginosa, were tested. After 48 hours S. aureus was the bacterium most sensitive to the 70% ethanol extract of pollen, A. fumigatus was the most sensitive microscopic fungus (70% ethanol) and C. glabrata the most sensitive yeast (70% methanol). Microorganisms most sensitive to propolis extracts were L. monocytogenes, A. fumigatus (70% ethanol) and G. candidum (70% methanol). Most sensitive to beeswax extracts were E. coli, A. niger and C. tropicalis