Acceptable Tolerance Limits Research Articles

Optimisation of springback predicted by experimental and numerical approach by using response surface methodology

Bending has significant importance in the sheet metal product industry. Moreover, the springback of sheet metal should be taken into consideration in order to produce bent sheet metal parts within acceptable tolerance limits and to solve geometrical variation for the control of the manufacturing process. Nowadays, the importance of this problem increases because of the use of sheet-metal parts with high mechanical characteristics (high strength low alloy steel). This work describes robust methods of predicting springback of parts in 3D modelling subjected to bending and unbending deformations. Also the effects of tool geometry in the final shape after springback are discussed. The first part of this paper presents the laboratory experiments in wiping die bending, in which the influence of process variables, such as die shoulder radius, punch-die clearance, punch nose radius and materials properties are discussed. The second part summarises the finite element analysis by using ABAQUS software and compares these results with some experimental data. The final results of the FEM simulation are in good agreement with the experimental ones. An optimisation methodology based on the use of experimental design method and response surface technique is proposed in the third part of this paper. This makes it possible to obtain the optimum values of clearance between the punch and the die and the optimum die radius, which can reduce the springback without cracking and damage of product.

Spatial registration of multichannel multi-subject fNIRS data to MNI space without MRI

The registration of functional brain data to the common brain space offers great advantages for inter-modal data integration and sharing. However, this is difficult to achieve in functional near-infrared spectroscopy (fNIRS) because fNIRS data are primary obtained from the head surface and lack structural information of the measured brain. Therefore, in our previous articles, we presented a method for probabilistic registration of fNIRS data to the standard Montreal Neurological Institute (MNI) template through international 10–20 system without using the subject's magnetic resonance image (MRI). In the current study, we demonstrate our method with a new statistical model to facilitate group studies and provide information on different components of variability. We adopt an analysis similar to the single-factor one-way classification analysis of variance based on random effects model to examine the variability involved in our improvised method of probabilistic registration of fNIRS data. We tested this method by registering head surface data of twelve subjects to seventeen reference MRI data sets and found that the standard deviation in probabilistic registration thus performed for given head surface points is approximately within the range of 4.7 to 7.0 mm. This means that, if the spatial registration error is within an acceptable tolerance limit, it is possible to perform multi-subject fNIRS analysis to make inference at the population level and to provide information on positional variability in the population, even when subjects' MRIs are not available. In essence, the current method enables the multi-subject fNIRS data to be presented in the MNI space with clear description of associated positional variability. Such data presentation on a common platform, will not only strengthen the validity of the population analysis of fNIRS studies, but will also facilitate both intra- and inter-modal data sharing among the neuroimaging community.

Optimisation of Springback Predicted by Experimental and Numerical Approach by Using Response Surface Methodology

Bending has significant importance in the sheet metal product industry. Moreover, the springback of sheet metal should be taken into consideration in order to produce bent sheet metal parts within acceptable tolerance limits and to solve geometrical variation for the control of manufacturing process. Nowadays, the importance of this problem increases because of the use of sheet-metal parts with high mechanical characteristics (High Strength Low Alloy steel). This work describes robust methods of predicting springback of parts in 3D modelling subjected to bending and unbending deformations. Also the effects of tool geometry in the final shape after springback are discussed. The first part of this paper presents the laboratory experiments in wiping die bending, in which the influence of process variables, such as die shoulder radius, punch-die clearance, punch nose radius and materials properties were discussed. The second part summarises the finite element analysis by using ABAQUS software and compares these results with some experimental data. It appeared that the final results of the FEM simulation are in good agreement with the experimental ones. An optimisation methodology based on the use of experimental design method and response surface technique is proposed in the third part of this paper. That makes it possible to obtain the optimum values of clearance between the punch and the die and the optimum die radius which can reduce the springback without cracking and damage of product.

Effect of Fixture Compliance on Thermally Enhanced Edge Registration in Microlamination

Microlamination involves the patterning, registration, and bonding of thin layers of material, called laminae, to produce highly paralleled, spatially intensified microchannel systems for the bulk processing of mass and energy. A Thermally Enhanced Edge Registration (TEER) technique has been developed for precision aligning large numbers of laminae in diffusion-bonding processes based on the differential thermal expansion between the laminae and bonding fixture. However, fixture tolerances necessary to promote buckle-free TEER bonding have been found to be very small (below 10 μm). This research focuses on the development of a new approach to thermal registration based on fixture compliance to permit looser fixture tolerances. An analysis based on both fin-buckling behavior and the compliance of the fixture is implemented to investigate the tolerance limit of a compliant TEER fixture. Experiments are conducted to verify the theoretical model. Results show that a compliant fixture can permit an acceptable tolerance limit in TEER.

First evidence of Dinophysistoxin-1 ester and carcinogenic polycyclic aromatic hydrocarbons in smoked bivalves collected in the Patagonia fjords

Diarrhetic shellfish poisoning (DSP) is a gastrointestinal disease caused by fat-soluble polyether toxins produced by dinoflagellates and accumulated in shellfish. Up to the present, only four fat-soluble polyethers have been known as diarrhetic shellfish toxins. Among them,*** Okadaic acid, Dinophysistoxin-1, Dinophysistoxin-2 and Dinophysistoxin-3. Outbreaks associated with DSP have occurred in the Chilean Patagonia fjords since 1970. Native people, who live in small communities close to the southern fjords, smoke fresh shellfish. During this popular smoking procedure, they impregnate the shellfish with polycyclic aromatic hydrocarbons, as incomplete combustion products, which are potent carcinogenic compounds, this product is sold in local markets without phycotoxins analysis or inclusion in any monitoring program. The present paper shows, DSP phycotoxins quantitation, using high performance liquid chromatography with fluorescent and mass spectrometric detection and the measurements of polycyclic aromatic hydrocarbons by gas chromatography with mass detection, in smoked shellfish samples. The presence of Dinophysistoxin-3, the Dinophysistoxin-1 ester (7- O-acyl-derivatives of dinophysistoxin-1), was assessed in all shellfish samples analyzed. The 7-OH in Dinophysistoxin-1 was esterified with palmitic fatty acid. The shellfish meat contains seven polycyclic aromatic hydrocarbons, among them fluoranthene, phenanthrene, anthracene, pyrene and benzo[a]pyrene. The gas chromatography-mass spectrometry analysis showed four of the six most frequent carcinogenic polycyclic aromatic hydrocarbons reported. The content of benzo[a]pyrene in the Razor Clam and Ribbed Mussel were 78.61 and 4.94 ng/g of shellfish dry weight, respectively. In both cases the benzo[a]pyrene amounts were greater than the acceptable tolerance limits of 1 μg/kg of sample. The Razor Clam samples also show amount further above the maximum label regulated by FAO/WHO (10 μg/kg). The presence of both type of compounds in the smoked shellfish samples analyzed, correspond to a dangerous combination, where the polycyclic aromatic hydrocarbons are carcinogenic compounds by themselves and DTX-1, is a potent tumor promoter.

Thickness Tolerance for Portland Cement Concrete Pavements

The thickness tolerance limit currently used by the Texas Department of Transportation for portland cement concrete pavements was developed about 50 years ago, when the pavement thickness was normally less than 10 in., and no additional study on the tolerance limit has been conducted since its development. Because the current thickness tolerances are independent of the design pavement thickness, they are very tight, especially for thicker pavements. These tight tolerances give difficulties in construction and in the use of nondestructive testing (NDT) methods for slab thickness determination because errors of NDT methods depend on the thickness. In this study, the sensitivity analysis of the slab thickness has been conducted to investigate whether the current thickness tolerance can be loosened and to propose acceptable thickness tolerance limits. The concepts to find the thickness tolerance have been developed on the basis of various methods, including the AASHTO pavement life prediction equation, the mechanistic distress prediction model, and fatigue failure models. The sensitivity of slab thickness to pavement performance has been investigated with those methods. The analysis results clearly show that the thickness tolerance should be dependent on pavement thickness. On the basis of the analysis results, reasonable approaches for thickness tolerance determination have been proposed.

An experimental study on the examination of springback of sheet metals with several thicknesses and properties in bending dies

The bending dies have significant importance in the sheet metals product industry. Moreover, the springback of the sheet metal should be taken into consideration in the bending die design. The amount of springback should be known in order to produce bent sheet metal parts within acceptable tolerance limits. In this research, an experimental study has been carried out on the determination of springback of bent products. Hence, the amount of springback of several sheet metals with different bending angles was obtained on a modular “V” bending die, which was designed and constructed, and the springback graphics were plotted. The results showed that these are in line with the results of previous researchers. The springback graphics for six different kinds of materials were realised by using four different bending methods in 18 different modular dies. The effects of bending methods on springback and convenience of the obtained graphics were discussed in detail. The results of the tests were evaluated statistically by using a personal computer and converted into graphics and tables. The useful data for practical design of bending dies by taking the springback into consideration was achieved with this study.

Quarantine problems: An analytical approach with special reference to palm weevils and phytonematodes

Regulatory control can prevent further spontaneous introduction of alien pests to Egypt or slow down the rate of spread of several recently introduced plant pests and diseases, limit their damage and/or allow time to develop alternative management strategies. The problem essentially is the impracticability of detecting the pest at its initial infestation site at a sufficiently early stage to have any chance of eradicating it. Pest spread to secondary foci within the country should be blocked through quarantine and certification programmes. Recognizing that zero tolerance requires sampling every unit in the lot, the default strategy is to define an acceptable tolerance limit for each pest sampled. The binomial probability distribution is presented as a base for determining probabilities of detecting various infestation levels as increasing numbers of samples are collected. Such a method saves time, labour and money in the detection and ensures the relative proportional certainty emanating from the inspected sample to the actual matter. However, a zero tolerance is required for the palm weevils. Neither Poisson nor the negative binomial distributions can be applied to such a zero tolerance or for soil sampling size to solely prove that the nematode is absent. Eventually, the tolerance limit must be backed up by sound technical information and consequent judgements for each specific case. Therefore, comprehensive precautions should be implemented for complete protection against pests and diseases as yet not found in Egypt.

Gas chromatography-mass spectrometric determination of polycyclic aromatic hydrocarbons in five species of fish from three sites in the Arabian Gulf

A gas chromatography-mass spectrmetroic (GC-MS) method was developed to measure six polycyclic aromatic hydrocarbons (PAHs) in 54 fish samples. Five fish species highly consumed by the local population (shrimps, Emperors, Rabbitfish, Doublebar Bream and Greasy Grouper) were selected from three different sites on the Gulf coast of Saudi Arabia where agricultural, municipal and petroleum industry activities take place. Variations in PAH levels among the three sites were not significant. Total concentrations of PAHs benzo(a)anthracene, chrysene, and benzo(b)fluoranthene ranged from non-detectable to 44.9 w g kg−1. In this study, concentrations of benzo(a)anthracene, chrysene, benzo(b)fluoranthene and total PAHs greater than the acceptable tolerance limit (1 w g kg−1) were found in 68.5, 40.7, 51.9 and 83.3% of the fish samples, respectively. PAH contents in fish vary considerably with species; Doublebar bream contain the highest while shrimps contain the lowest. This pilot study clearly shows that the consumption of fish could be a source of exposure of the local population to PAHs. Since there is a consensus on the substantial contribution of PAHs to cancer in humans, it would be interesting to conduct further research in order to determine the magnitude of the problem along other coastal regions of Saudi Arabia.

Mycoflora and occurrence of fumonisins in freshly harvested and stored hybrid maize

The study of the mycoflora in stored grain permits an evaluation of cereal storage conditions that affect grain deterioration and the risk of mycotoxin contamination. Abiotic factors can directly affect the relative frequency of fungal populations in stored grain. The aim of the present work was to study the influence of abiotic factors on variations of mycoflora of freshly harvested and stored maize in Brazil and the occurrence of fumonisins. Samples (195) of three hybrids of maize were analyzed monthly during one year. Microbiological analysis revealed a predominance of Fusarium spp, which presented the greatest total number of colony forming units per gram in the three hybrids, namely: Br 201 (11×10 4 to 5340×10 4 CFU/g), C 125 (18×10 4 to 2790×10 4 CFU/g) and Cx 322 (25×10 4 to 2940×10 4 CFU/g), followed by Penicillium spp, Aspergillus spp and 10 other fungal genera. Fusarium moniliforme Sheldon was the most prevalent species (59.2% of Fusarium isolates in Br 201, 55.4% in C 125 and 69.2% in Cx 322). Fusarium spp showed significant negative correlations with mean temperature and relative humidity of the air. Higher temperatures and relative humidity at the end of the study and high moisture content at the beginning of the study were observed. The CFU/g values recorded for the three predominant genera exceeded the internationally accepted tolerance limits. The mycotoxicological evaluation indicated contamination of 176 samples (90.2%) with fumonisin B 1 and of 190 samples (97.4%) with fumonisin B 2.

A Sensitivity Study on Optimum Delayed Feedback Vibration Absorber

A sensitivity analysis is presented for a novel tuned vibration absorber. The active tuning of the absorber is achieved using partial state feedback with a controlled time delay. The final structure, which is named Delayed Feedback Vibration Absorber (DFVA), is optimized to yield minimum Mpeak of the primary system involved for a given wide band of excitation frequencies. The optimization is performed over the absorber’s structural properties and the feedback control parameters. An optimal tuning over optimally designed passive absorber is conducted first, and separately a collective optimization over both the absorber structure and the control is studied. The assurance of the stability of the time-delayed system, which forms a critical constraint on the optimization, is also discussed. Regardless of the nature of the optimal operation, the parametric variations in the structure can influence the vibration absorption performance significantly. This concern is addressed via a sensitivity analysis. Primarily, the variations on the absorber stiffness and damping properties are studied. The findings of this effort provide tools for determining the acceptable tolerance limits of the absorber properties. [S0022-0434(00)02202-4]

Radiation myelopathy following transplantation and radiotherapy for non–Hodgkin’s lymphoma

Background: Combined modality therapy with chemotherapy and radiotherapy has become increasingly popular in the management of solid malignancies. However, unexpected toxicities may arise from their interactions. Methods and Materials: We report the case of a young woman with a large mediastinal non–Hodgkin’s lymphoma who underwent high-dose chemotherapy with autologous bone marrow transplantation and involved field radiotherapy, and who developed radiation myelopathy after a latent period of only 3 months. The spinal cord dose did not exceed 40.3 Gy in 22 fractions over 4.5 weeks, which is well within accepted tolerance limits. She had no other identifiable risk factors for radiation myelopathy, suggesting an adverse drug–radiation interaction as the most likely cause of her injury. Results and Conclusions: This represents the first report of radiation myelopathy at accepted safe radiation doses following high-dose chemotherapy with autologous bone marrow transplantation, and we recommend caution in the choice of radiotherapeutic dose in this setting.

Backcountry Encounter Norms, Actual Reported Encounters, and Their Relationship to Wilderness Solitude

Backcountry backpackers' norms concerning the maximum acceptable tolerance limits for visual-social contacts at three encounter sites (trailhead, trail, and campsite) were examined in the Great Smo...

Apparatus and method whereby wave energy is correlated with geometry of a manufactured part or the like or to positional relationships in a system

A way of automatically inspecting a machined part, for example, to a tolerance of 0.001 inches. A minicomputer monitors a change in phase, for example, of wave energy impinging upon a sample part and compares it with a change in phase of such energy for a standard or master part, any difference between the monitored changes being interpreted to determine if the sample is within acceptable tolerance limits. The inspection approach described uses no moving parts and can be used to inspect many dimensions of a part simultaneously in less than a second. Acoustic waves or microwave electromagnetic wave energy can be used to inspect parts of any shape. The inspection system disclosed can be used, as well, to monitor the geometry of an object over time to note any changes in said geometry. And the concepts of the inspection system can be employed in conjunction with robot-controlled devices to provide close-positioning data for such devices.

The relative biological effectiveness of fast-neutron and x-radiation; survival and cataract studies of Swiss mice.

The relative biological effectiveness (RBE) of fast-neutron and x-radiation is a concern of persons responsible for radiation safety measures, as well as those interested in the mechanisms of radiobiological action. The RBE of fast neutrons and x-rays has been found to vary when different criteria, different tissues, or different exposure patterns have been utilized in deriving the ratio (1, 2). In establishing an acceptable tolerance limit for neutron radiation, therefore, the most unfavorable effectiveness ratios must be considered. An earlier study by Evans (2) indicated that lens damage was one of the more critical biological effects of low-level neutron irradiation. Further study of the relative cataractogenic effectiveness of fast-neutron and x- or gamma radiation was then begun at this and other laboratories. Because the dosimetry of fast-neutron radiation had not been standardized, it seemed prudent also to determine a biological unit of exposure, the 30-day LD 50. This paper summarizes our observations on survival and cataract development after single exposures to several neutron sources as compared with observations after x-irradiation. Exposure Methods The animals utilized in all experiments were mice of an albino Swiss stock raised in our laboratory. At weaning time, the sexes were separated and put into stainless steel boxes, 8 mice of comparable age (no more than five days difference in date of birth) per box. The occupants of any one box were seldom all litter mates, thus tending to randomize the sampling. The sawdust in the boxes was changed three times per week; food and water were available at will. Mice from the stock colony were prepared for experimental use by clipping the toes to insure proper identification. The mice were irradiated at two and a half to three and a half months of age. The several boxes housing mice of the same age (± two days) were usually divided into two groups, one group for neutron irradiation and the other for x-irradiation. The several boxes in each group were randomly assigned to dose levels scattered over the entire range of exposures under investigation. The animals arbitrarily chosen as controls were not irradiated, but were otherwise transported, confined, and handled like the irradiated animals. In similar fashion, mice of different ages within the range of two and a half to three and a half months were allocated to the same or interspersed dose levels. With one exception (exposures to fission neutrons), experiments were repeated several times during a period of two to three years. The results of all repeated experiments have been combined for the final summary. X-radiation: The studies of x-radiation effects, which have extended over a period of seven years, were begun with the following exposure factors: 200 kv, 5 ma, 0.25 mm. Cu plus 1.0 mm.

The Influence of Item Modality on the Dimension Measured by a Test

WHEN A battery of proficiency tests for bombing-navigation systems mechanics was val idated, one of the tests, designed to measure ability to read dials and indicators, failed to dis criminate significantly among mechanics of dif ferent levels of proficiency. A task-o rie nted analysis and the unanimous opinion of experts in systems maintenance both indicated that the abil ity to read dials and indicators is an important part of routine maintenance skill. In seeking to account for the apparent failure of the te s t to measure this ability, it was suggested that the form of the items might be the cause. The 34 items on the test are all in five alter native multiple choice form. Each item pre sents a drawing of one of the dials in the system with the hand pointing to a typical value. Four of the responses consist of more or less plaus ible readings, and the fifth a none of the above is correct' ' type of statement. The mechanic being tested is supposed to read the dial and in dicate which response agrees best with his read ing. Actually, what may be happening is that the mechanic is making comparisons between the responses and the picture of the dial, and elim inating some or all of the responses as obvious ly wrong. The task offered by the test probably does not resemble the task he must perform on the job, when, rather than choose among four readings, he must get the reading from the dial without aid of any sort. This possibility seemed strong enough to warrant investigation, so a second form of the test was constructed, consisting of the same 34 items in completion form?that is, with blanks in which the mechanic was to write the value on the dial as he read it. His reading was consid ered correct if it fell within accepted tolerance limits (for that dial) of the actual reading. A cross-validation study of the battery was contemplated in the future. In the meantime, a decision was made to administer the two forms to graduates of a training course for mechanics and to analyze their scores to see whether or not the completion form measures the same thing that the multiple-choice form measures. If it does measure the same thing, it is no better than the multiple-choice test and there will be no need to include either form in the battery to be cross validated; if it measures something else, it will be worthwhile to include it.