Estimating material elasticity by spherical indentation load-relaxation tests on viscoelastic samples of finite thickness

A two-step viscoelastic spherical indentation method is proposed to compensate for 1) material relaxation and 2) sample thickness. In the first step, the indenter is moved at a constant speed and the reaction force is measured. In the second step, the indenter is held at a constant position and the relaxation response of the material is measured. Then the relaxation response is fit with a multi-exponential function which corresponds to a three-branch general Maxwell model. The relaxation modulus is derived by correcting the finite ramp time introduced in the first step. The proposed model takes into account the sample thickness, which is important for applications in which the sample thickness is less than ten times the indenter radius. The model is validated numerically by finite element simulations. Experiments are carried out on a 10% gelatin phantom and a chicken breast sample with the proposed method. The results for both the gelatin phantom and the chicken breast sample agree with the results obtained from a surface wave method. Both the finite element simulations and experimental results show improved elasticity estimations by incorporating the sample thickness into the model. The measured shear elasticities of the 10% gelatin sample are 6.79 and 6.93 kPa by the proposed finite indentation method at sample thickness of 40 and 20 mm, respectively. The elasticity of the same sample is estimated to be 6.53 kPa by the surface wave method. For the chicken breast sample, the shear elasticity is measured to be 4.51 and 5.17 kPa by the proposed indentation method at sample thickness of 40 and 20 mm, respectively. Its elasticity is measured by the surface wave method to be 4.14 kPa. © 2011 IEEE.

Ultrastructural mechanical and material characterization of fossilized bone

Bone plays a key role in the paleontological and archeological records and can provide insight into the biology, ecology and the environment of ancient vertebrates. Examination of bone at the tissue level reveals a definitive relationship between nanomechanical properties and the local organic content, mineral content, and microstructural organization. However, it is unclear as to how these properties change following fossilization, or diagenesis, where the organic phase is rapidly removed and the remaining mineral phase is reinforced by the deposition of apatites, calcites, and other minerals. While the process of diagenesis is poorly understood, its outcome clearly results in the potential for dramatic alteration of the mechanical response of biological tissues. In this study, fossilized specimens of mammalian long bones, collected from Colorado and Wyoming, were studied for mechanical variations. Nanoindentation performed in both longitudinal and transverse directions revealed preservation of bone's natural anisotropy as transverse modulus values were consistently smaller than longitudinal values. Additionally, modulus values of fossilized bone from 35.0 to 89.1 GPa increased linearly with logarithm of the sample's age. Future studies will aim to clarify what mechanical and material elements of bone are retained during diagenesis as bone becomes part of the geologic milieu. © 2007 Materials Research Society.

Studies on the suitability of HDPE material for gill nets

The suitability of HDPE yarn and HDPE twine in place of nylon for gill nets has been studied. As regards total catch nylon gill net is found to be better than HDPE nets. However, statistical analysis of the catch in respect of quality fishes shows that HDPE yarn nets are equally efficient as nylon nets.

Status of the shrimp sector in Bangladesh in the context of HACCP and trade issues: a review

Shrimp culture in Bangladesh has emerged as an important aquaculture industry over the last three decades although its culture in greater parts of the farming area is done in traditional ways. In the meantime, the government of Bangladesh has taken necessary measures along with the private sectors to increase production, upgrade processing industries and to promote export performance. Long supply chain in raw material collection, inadequate infrastructure facilities, poor level of cool chain and lack of adequate HACCP-based training on hygiene and sanitation of different groups of people involved in the field level are the main problems of quality loss of raw materials. Shortage of raw materials results in poor capacity utilization of the processing plants. The growth of bagda (P. monodon) hatchery has expanded rapidly over the last few years, remaining mostly concentrated in Cox's Bazar region is enough to meet the target production. However, there is a shortage of pelleted shrimp feed in Bangladesh. A large number of export processors are now producing increasing amounts of value-added products such as individually quick-frozen, peeled and divined, butterfly cut shrimp, as well as cooked products. The export earnings from value added products is about half of the total export value. About 95% of total fish products are exported to European countries, USA and Japan and the remaining to the Southeast Asia and the Middle East. Most of the EU approved shrimp processing industries have been upgraded with laboratory facilities and provided HACCP training to their workers. As of now, HACCP is applied on the processing plants, but to ensure the quality of raw materials and to reduce risks, shrimp farms are also required to adopt HACCP plan. There is increased pressure time to time from importing countries for fish processors to establish effective quality assurance system in processing plants. Fish Inspection and Quality Control (FIQC) of the Department of Fisheries while having moderately equipped laboratories with chemical, bio-chemical and microbiological testing facilities and qualified technical personnel, the creation of facilities for testing of antibiotics is underway. FIQC mainly supervises quality aspects of the processing plants and has little or no control over raw material supply chains from farm to processing plants. Bangladesh export consignments sometimes face rejection due to reported poor quality of the products. Three types of barriers are reported for export of shrimp to EU countries. These are:(1) government participation in trade and restrictive practices (state aid, countervailing duties, state trading enterprises, government monopoly practices), customs and administrative entry procedures (anti-dumping duties, customs valuation, classification, formalities, rules of origin); (2) technical barriers to trade or TBT (technical regulations, standards, testing, certification arrangement); (3) specific limitations (quantitative restrictions, import licensing, embargoes, exchange control, discriminatory sourcing, export restraints, measures to regulate domestic prices, requirements concerning marking, labeling and packaging).