Experimental techniques for ductile damage characterisation

Ductile damage in metallic materials is caused by the nucleation, growth and coalesce of voids and micro-cracks in the metal matrix when it is subjected to plastic strain. A considerable number of models have been proposed to represent ductile failure focusing on the ultimate failure conditions; however, only some of them study in detail the whole damage accumulation process. The aim of this work is to review experimental techniques developed by various authors to measure the accumulation of ductile damage under tensile loads. The measurement methods reviewed include: stiffness degradation, indentation, microstructure analysis, ultrasonic waves propagation, X-ray tomography and electrical potential drop. Stiffness degradation and indentation techniques have been tested on stainless steel 304L hourglass-shaped samples. A special interest is placed in the Continuum Damage Mechanics approach (CDM) as its equations incorporate macroscopic parameters that can represent directly the damage accumulation measured in the experiments. The other main objective lies in identifying the strengths and weaknesses of each technique for the assessment of materials subjected to different strain-rate and temperature conditions

Keberlanjutan Sistem Budi Daya Ternak Sapi Perah Pada Peternakan Rakyat Di Kabupaten Bogor

EnglishDairy farming system in Bogor Regency deals with threatening problems. This research aims to assess and to analyze sustainability of dairy farming system of smallholding farms in Bogor Regency. The respondents consisted of dairy farm area (Kunak) and smallholding farms in Cisarua District. Approach used in this study was a rapid appraisal for dairy farm system (Rap-Sibusape) using a multidimensional scaling (MDS) method. Results showed that smallholders in Cisarua and Kunak had index values of system dairy farms sustainability of 51.25 and 54.12, respectively. It indicated that the two areas are quite sustainable. Analysis five sustainable dimensions (ecology, economy, socio-culture, infrastructure technology, and institutional law) showed that ecology was sustainable on Kunak, and economy and socio-culture were not sustainable on both Kunak and dairy farm in Cisarua. Leverage analysis results showed that there were 15 out of 45 attributes influencing the sustainability index system. There were six key factors strongly influenced the system with low dependence among factors, i.e. (i) milk prices, (ii) feed carrying capacity, (iii) development cooperation, (iv) input subsidies, (v) micro finance, and (vi) socialization work. Improving dairy cattle farming in Bogor Regency requires sustainability index value enhancement of 15 sensitive attributes focused on 6 key factors affecting the dairy cattle farming system.IndonesianPeternakan sapi perah di Kabupaten Bogor menghadapi permasalahan yang mengancam keberlanjutan sistem, seperti (i) keterbatasan pakan hijauan, (ii) penurunan jumlah peternak, (iii) rendahnya mutu susu, (iv) penyakit ternak, dan (v) terbatasnya sarana-prasarana agribisnis. Oleh karena itu, perlu dikaji status keberlanjutan sistem peternakan sapi perah di Kabupaten Bogor untuk memperoleh manfaat optimal dari kinerja sistem. Penelitian ini bertujuan untuk menilai dan menganalisis keberlanjutan sistem peternakan sapi perah rakyat di Kabupaten Bogor yang diwakili oleh Kawasan Usaha Ternak (Kunak) dan peternakan rakyat Cisarua dengan metode rapid appraisal sistem peternakan sapi perah (Rap-Sibusape) menggunakan pendekatan multidimensional scaling (MDS). Penilaian Rap-Sibusape menunjukkan Kunak dan peternakan rakyat Cisarua memiliki rataan nilai indeks keberlanjutan sebesar 51,25 dan 54,12 sehingga berkategori cukup berkelanjutan. Analisis lima dimensi keberlanjutan (ekologi, ekonomi, sosial-budaya, teknologi-infrastruktur, dan hukum-kelembagaan) menunjukkan dimensi ekologi tidak berkelanjutan pada Kunak, dimensi ekonomi dan sosial-budaya tidak berkelanjutan pada Kunak dan peternakan rakyat Cisarua. Analisis leverage menunjukkan terdapat 15 atribut dari 45 atribut berpengaruh terhadap indeks keberlanjutan sistem peternakan sapi perah. Analisis prospektif menunjukkan terdapat 6 faktor kunci berpengaruh kuat terhadap sistem dengan tingkat ketergantungan antarfaktor yang rendah namun berpengaruh besar terhadap sistem. Enam faktor kunci tersebut yakni: (i) harga susu 5 tahun terakhir, (ii) daya dukung pakan, (iii) perkembangan koperasi, (iv) tingkat subsidi input, (v) lembaga keuangan mikro, dan (vi) sosialisasi pekerjaan. Pengembangan sistem peternakan sapi perah Kabupaten Bogor memerlukan peningkatan nilai indeks keberlanjutan melalui pengelolaan dan perbaikan 15 atribut sensitif dengan fokus pada perbaikan 6 faktor kunci yang berpengaruh terhadap sistem peternakan sapi perah

The Effects of Air and Underwater Blast on Composite Sandwich Panels and Tubular Laminate Structures

The resistance of glass-fibre reinforced polymer (GFRP) sandwich panels and laminate tubes to blast in air and underwater environments has been studied. Procedures for monitoring the structural response of such materials during blast events have been devised. High-speed photography was employed during the air-blast loading of GFRP sandwich panels, in conjunction with digital image correlation (DIC), to monitor the deformation of these structures under shock loading. Failure mechanisms have been revealed by using DIC and confirmed in post-test sectioning. Strain gauges were used to monitor the structural response of similar sandwich materials and GFRP tubular laminates during underwater shocks. The effect of the backing medium (air or water) of the target facing the shock has been identified during these studies. Mechanisms of failure have been established such as core crushing, skin/core cracking, delamination and fibre breakage. Strain gauge data supported the mechanisms for such damage. These studies were part of a research programme sponsored by the Office of Naval Research (ONR) investigating blast loading of composite naval structures. The full-scale experimental results presented here will aid and assist in the development of analytical and computational models. Furthermore, it highlights the importance of support and boundary conditions with regards to blast resistant design

Air conditioning, comfort and energy in india's commercial building sector

Before India's building sector can fulfil its CO2 abatement potential, it is imperative for new build projects, especially those which provide for commercial and public functions, to eschew the energy-intensive designs that characterized western commercial buildings of the 20th century. In the absence of an adaptive thermal comfort standard specifically for India's climatic and cultural context, the current trend is simply to design airconditioned buildings to meet the stringent ASHRAE and ISO "Class A" comfort specifications. This paper proposes a holistic Post Occupancy Evaluation (POE) study of a cross section of Indian office buildings purposively stratified across a range of energy intensities with diverse environmental control systems and design approach in different climatic zones to develop an adaptive thermal comfort standard. By climatically adapting indoor design temperatures, the standard will offer India a low-carbon development pathway for its commercial building sector without compromising overall comfort or productivity

An experimental methodology to characterise post-necking behaviour and quantify ductile damage accumulation in isotropic materials

The development of ductile damage, that occurs beyond the point of necking in a tensile test, can be difficult to quantify. An experimental methodology has been developed to accurately characterise the post-necking deformation response of a material through continuous monitoring of the specimens shape up until rupture. By studying the evolution of the neck geometry, the correct values of the local stress and strain have been determined in samples of grade 304L stainless steel and C110 copper. Notched bar specimens of various notch acuities were examined enabling the effects of stress triaxiality on ductile fracture to be determined. The methodology developed has provided a robust framework for macroscopic measurements of ductile damage during the necking process. To characterise the material degradation process, the elastic modulus reduction method was employed on hourglass-shaped specimens of the same materials. Stiffness degradation was measured using a small gauge extensometer during uninterrupted tensile tests with partial elastic unloadings. A metallographic study was conducted on progressively damaged specimens in order to validate the macroscopic damage measurements. A new non-linear ductile damage accumulation law has been developed and calibrated, which provides an advanced representation of the experimental results, and a significant improvement compared to linear accumulation models frequently employed. This realistic modelling approach considers the degradation of the material when it has undergone severe plastic deformation, and provides a more accurate representation of the near failure behaviour by considering the effects of stress triaxiality. The methodology provides accurate data for damage model development and calibration, to improve the predictions of remnant life from ductile damage in engineering components

Amyloid-β peptide 37, 38 and 40 individually and cooperatively inhibit amyloid-β 42 aggregation

The pathology of Alzheimer's disease is connected to the aggregation of β-amyloid (Aβ) peptide, which in vivo exists as a number of length-variants. Truncations and extensions are found at both the N- and C-termini, relative to the most commonly studied 40- and 42-residue alloforms. Here, we investigate the aggregation of two physiologically abundant alloforms, Aβ37 and Aβ38, as pure peptides and in mixtures with Aβ40 and Aβ42. A variety of molar ratios were applied in quaternary mixtures to investigate whether a certain ratio is maximally inhibiting of the more toxic alloform Aβ42. Through kinetic analysis, we show that both Aβ37 and Aβ38 self-assemble through an autocatalytic secondary nucleation reaction to form fibrillar β-sheet-rich aggregates, albeit on a longer timescale than Aβ40 or Aβ42. Additionally, we show that the shorter alloforms co-aggregate with Aβ40, affecting both the kinetics of aggregation and the resulting fibrillar ultrastructure. In contrast, neither Aβ37 nor Aβ38 forms co-aggregates with Aβ42; however, both short alloforms reduce the rate of Aβ42 aggregation in a concentration-dependent manner. Finally, we show that the aggregation of Aβ42 is more significantly impeded by a combination of Aβ37, Aβ38, and Aβ40 than by any of these alloforms independently. These results demonstrate that the aggregation of any given Aβ alloform is significantly perturbed by the presence of other alloforms, particularly in heterogeneous mixtures, such as is found in the extracellular fluid of the brain. This journal i