Minimum Standoff Distance Research Articles

Effect of Abrasive Water Jet Parameters on the Drilling of Aluminum Foam Sandwiched with Glass Fiber Polymer Composites

To attain good geometric shape and size, machining of high-strength metal Fiber laminate becomes inevitable in the field of automotive industries. In this research, aluminum foam sandwiched with glass fiber reinforced polymer (GFRP) composites fabricated using a hand layup process. The glass Fiber composite was fabricated using aluminum foam with a thickness of 1 mm. The effect of abrasive water jet parameters such as pressure (P), stand-off distance (L), and nozzle diameter (D) on material removal rate (MRR) and Kerf angle (Ka) and Surface roughness were investigated. The results were compared without aluminum foam composites. Glass fiber composites with aluminum foam reduced the kerf angle by 44.18 %, and surface roughness (Ra) by 41.77 % as compared with glass fiber composites without aluminum foam. From the investigation, it was noticed that maximum pressure (220 Bar) and minimum stand-off distance (1mm) were optimum parameters for reducing the kerf angle and surface roughness. Also, Optical images of the hole were analyzed for surface quality.

Reduction of Cracks in Marble Appeared at Hydro-Abrasive Jet Cutting Using Taguchi Method.

The appearance of cracks in brittle materials in general and in marble, in particular, is a problem in the hydro-abrasive jet cutting process. In this paper is presented a method to reduce the appearance of cracks when cutting with a hydro-abrasive jet of marble by using statistical analysis. The Taguchi method was used, establishing the main parameters that influence the process. Research design was based on performing experiments by modifying the parameters that influence the process. In this way, it has been shown that the stochastic effects resulting from the marble structure can be reduced. A careful study was made of the behavior of marble under the action of the hydro-abrasive jet, and of the behavior of the whole process in the processing of brittle materials. Results of experiments confirmed the hypothesis that statistical analysis is a procedure that can lead to a decrease in the number of cracks in processing. The measurement was performed with precise instruments and analyzed with recognized software and according to the results obtained, the reduction of the number of cracks is achieved through use of low pressure, a minimum stand-off distance and a small tube diameter. In this way, the paper presents a new and effective tool for optimizing the cutting with a hydro-abrasive jet of marble.

Effect of the threaded nozzle on delamination and surface texture of PEEK CF30 composite machined by abrasive jet

Purpose The purpose of this study is to bring out the machining characteristics of abrasive jet machining on carbon fibre reinforced thermoplastic composites utilized in aerospace and biomedical applications. Biocompatibility materials such as carbon fibres and polyether thermoplastics, like polyether ether ketone (PEEK) are widely used in trauma and orthopaedic surgery. Due to the heterogeneity, layered construction of reinforcing phase bonds with a resin matrix and abrasiveness of the reinforcing fibre, traditional drilling of carbon fibre-reinforced composites (CFRPs) are always challenging task. Design/methodology/approach An investigation is carried out using abrasive jet machine for drilling PEEK filled with 30 Wt.% carbon fibre (CF 30) using threaded and unthreaded nozzle to study the effect of abrasive jet process variables on surface roughness (Ra) and delamination factor (DF). Pressure (P) and stand-off distance (SOD) as important technological abrasive jet factors were evaluated. It is found that higher abrasive jet pressure and minimum SOD maybe selected to achieve minimum delamination. Findings The study further reported that the threaded nozzle minimized the surface roughness by 43% and delamination factor up to 12%. Originality/value This study of experimenting and observing the machining characteristics of CF30 by using a threaded nozzle is being tried for the first time and the results are deliberated.

Sensor orientation and other factors which increase the blast overpressure reporting errors.

This study compared the response of the wearable sensors tested against the industry-standard pressure transducers at blast overpressure (BOP) levels typically experienced in training. We systematically evaluated the effects of the sensor orientation with respect to the direction of the incident shock wave and demonstrated how the averaging methods affect the reported pressure values. The evaluated methods included averaging peak overpressure and impulse of all four sensors mounted on a helmet, taking the average of the three sensors, or isolating the incident pressure equivalent using two sensors. The experimental procedures were conducted in controlled laboratory conditions using the shock tube, and some of the findings were verified in field conditions with live fire charges during explosive breaching training. We used four different orientations (0°, 90°, 180°, and 270°) of the headform retrofitted with commonly fielded helmets (ACH, ECH, Ops-Core) with four B3 Blast Gauge sensors. We determined that averaging the peak overpressure values overestimates the actual dosage experienced by operators, which is caused by the reflected pressure contribution. This conclusion is valid despite the identified limitation of the B3 gauges that consistently underreport the peak reflected overpressure, compared to the industry-standard sensors. We also noted consistent overestimation of the impulse. These findings demonstrate that extreme caution should be exercised when interpreting occupational blast exposure results without knowing the orientation of the sensors. Pure numerical values without the geometrical, training-regime specific information such as the position of the sensors, the distance and orientation of the trainee to the source of the blast wave, and weapon system used will inevitably lead to erroneous estimation of the individual and cumulative blast overpressure (BOP) dosages. Considering that the 4 psi (~28 kPa) incident BOP is currently accepted as the threshold exposure safety value, a misinterpretation of exposure level may lead to an inaccurate estimation of BOP at the minimum standoff distance (MSD), or exclusion criteria.

Modeling of surface roughness in abrasive water jet machining of AZ91 magnesium alloy using Fuzzy logic and Regression analysis

Surface irregularity of machined parts is one of the major machining characteristics that play an important role in determining the quality of engineering components. Abrasive water jet cutting has been proven to be an effective technology for processing various engineering materials. This work deals with the abrasive water jet machining of magnesium alloy (AZ 91). The abrasive water jet experiment was designed using response surface methodology (RSM). Surface roughness was measured on the machined magnesium alloy. Three variable input parameters such as water pressure (WP), Traverse speed (TS), and Stand-off distance (SOD) were selected as process parameters. Surface roughness was predicted fuzzy logic. Regression equation was used for predicting the SR value. From this investigation, it was observed that maximum pressure and minimum stand-off distance caused reduction in the surface roughness in the abrasive water jet machining of AZ91 magnesium alloy. Further, the developed fuzzy model was used to validate the results and it was found that the predicted values were in good agreement with a 95% confidence level. It was also evident that the fuzzy technique is helpful for better prediction of the experimental.

Study on key parameters of a new abrasive flow machining (AFM) process for surface finishing

The conventional abrasive flow machining (AFM) and its derivatives (i.e., magneto, electro-chemical, and ultrasonic-aided AFMs) demand special machining devices, which limits the application and dissemination of AFM. A new AFM is developed in this study, which demands no extra special devices except for a tool bar made with cemented carbide. The effect of dynamic viscosity of abrasive medium, standoff distance, and tool bar rotating speed on pressure and velocity distributions of flow field is investigated using a numerical model. Moreover, experiments are conducted to explore the influence of abrasive-laden medium and process key parameters on this new AFM finishing effect. The results indicate that the pressure and velocity of flow field reach their maximum at the middle of the minimum standoff distance between tool bar and workpiece. The optimum abrasive grain size utilized in this AFM is found to be related to the minimum standoff distance between tool bar and workpiece during finishing process. The obtained optimum tool bar rotating speed, traverse speed, and number of processing cycles are 19,200 r/min, 500 mm/min, and 500 cycles, respectively. This new AFM is anticipated to become an efficient and economic tool for surface finishing.

Effects of Hydrogen Addition on the Standoff Distance of Premixed Burner-Stabilized Flames of Various Hydrocarbon Fuels

The quenching distance of premixed hydrocarbon flames is of significant importance for studying flame/wall interactions and for understanding the unburned hydrocarbon emissions of internal combustion engines. Motivated by the fact that the standoff distance of premixed burner-stabilized flames could be used to investigate the behavior of head-on quenching distance of freely propagating flames despite the different physics involved, a parametric investigation on the standoff distances of methane, ethane, and propane burner-stabilized flames was conducted numerically using a detailed chemical kinetic mechanism, with a focus on the effects of hydrogen addition. Specifically, the minimum standoff distance was found to quantitatively correlate with the head-on quenching distance of premixed flames. The variations of the minimum standoff distance as a function of hydrogen fractions were then investigated in detail. The results showed that as hydrogen fraction increased, the minimum standoff distances decreased ...

Evaluation of Welding Parameter's Effects on Corrosion Behavior of Bronze-Carbon Steel Dual-Layer Explosion Welded Joint at Salt Enviroment

In the current investigation, corrosion behavior and microstructural variations of explosion-welded joint of bronze-carbon steel dual-layer plates were studied. The resultant curves of potentiodynamic's polarization tests demonstrated that the lowest corrosion rate was related to the sample with maximum explosive load thickness, and the highest corrosion speed was for the sample with minimum standoff distance. EIS test results of welded samples were indicative of creating a passive layer at the beginning of immersion process which showed that the polarization resistance has been reduced by increasing of explosive load thickness. So, the corrosion mechanism included two stages; at the beginning of immersion, for the samples with the lower thickness of explosive load, a passive layer would be created around the component due to higher concentration gradient and then, by removing of this layer, the galvanic couple determines the corrosion rate.

Damage and Risk Assessment for Single-Layer Reticulated Domes Subject to Explosive Blast Loads

In order to provide a better understanding of the dynamic behavior of single-layer reticulated domes subjected to explosive blast loads, a number of analyses are carried out on structures with different standoff distances ([Formula: see text]), explosive weights ([Formula: see text]), rise–span ratios ([Formula: see text] and other parameters. An equation for a structural damage factor is proposed to evaluate structural damage quantitatively. The damage states for single-layer reticulated domes are defined based on their structural dynamic performance and corresponding damage factors. Structural reliabilities for different standoff distances are obtained using the Monte-Carlo Analysis. A typical protective measure is bollards which are used to help ensure a minimum standoff distance. To illustrate the cost-effectiveness of such a protective measure, structural damage states and various losses, including direct and indirect economic loss and maimed and fatality loss, are considered for assessing the risk reduction, costs and benefits. It was found that the bollards significantly reduce the likelihood of structural progressive collapse or severe damage, and the optimal standoff distance can be determined.

Estimating safe scaled distances for columns subjected to blast

This paper is concerned with determining the minimum stand-off distance required to prevent column failures in reinforced concrete framed buildings. This is of interest because column failures can initiate progressive collapse, resulting in mass casualties. A technique is developed to determine the critical range at which failure will occur for a given weight of explosives and thus provide a safe scaled distance. The method is used to carry out a parametric study of a range of reinforced concrete columns of variable dimensions and strengths. The corresponding data were used to predict safe scaled distances for columns (with and without clearing). These values can be used to estimate the minimum stand-off distance required to prevent progressive collapses of buildings that may be subjected to deliberate blast loading.

Simplified design method for bridge piers subjected to unconfined blast hazards

The vulnerability of bridges to blast hazards is an increasing concern for engineers, government agencies, and the public. Blast hazards on structures can be classified as either accidental hazards or intentional blast attacks, and structures should be protected to mitigate these hazards. Current bridge design codes do not account for blast loading, and there is a need for guidelines for designing structures such as bridges and other structures to resist blast loads. The individual response of structural elements subjected to blast loads depends mainly on the standoff distance, charge weight, and the distribution of the blast pressure along the length of the loaded member. Structural components, such as bridge piers, subjected to blast hazards along with their connections, should be designed to have considerable ductility and energy absorption capacity. This paper presents a simplified design method for members subjected to unconfined blast loads, such as bridge piers. Estimating blast loads on a member due to specific blast scenario is complex. To simplify the analysis, dynamic blast loads were transformed into equivalent static loads, and simplified blast load response spectra were developed based on approximate blast pressure distributions. Blast response spectra can be used to analyze and design individual structural components subjected to blast loads in flexure, estimate the required ductility, and estimate the minimum standoff distance for the different probable blast charge weights. For complex critical structures, more rigorous analysis is needed, including the global response of the structure.

Acoustic properties of humpback whale songs

A vertical array of five hydrophones was used to measure the acoustic field in the vertical plane of singing humpback whales. Once a singer was located, two swimmers with snorkel gear were deployed to determine the orientation of the whale and position the boat so that the array could be deployed in front of the whale at a minimum standoff distance of at least 10 m. The spacing of the hydrophones was 7 m with the deepest hydrophone deployed at a depth of 35 m. An eight-channel TASCAM recorder with a bandwidth of 24 kHz was used to record the hydrophone signals. The location (distance and depth) of the singer was determined by computing the time of arrival differences between the hydrophone signals. The maximum source level varied between individual units in a song, with values between 151 and 173 dB re 1 microPa. One of the purposes of this study was to estimate potential sound exposure of nearby conspecifics. The acoustic field determined by considering the relative intensity of higher frequency harmonics in the signals indicated that the sounds are projected in the horizontal direction despite the singer being canted head downward anywhere from about 25 degrees to 90 degrees. High-frequency harmonics extended beyond 24 kHz, suggesting that humpback whales may have an upper frequency limit of hearing as high as 24 kHz.

Three-dimensional modeling of slab liquid jets used for heavy-ion fusion for beam line protection

IFE designs for thick liquid protection of heavy-ion inertial fusion reactors utilize banks of liquid jets to protect sensitive beam line components from neutrons and debris following target explosions. IFE designers must have knowledge of the surface quality of these jets in order to determine the distance between the jets and the ion beams that must propagate through the void spaces between them. Here, numerical simulations of such jet flows performed with the customized Flow3D solver are reported. These numerical simulations predicted no significant jet breakup in the region of interest, but did show surface and shape deformation that may end up determining the minimum standoff distance between jets and driver beams. The simulations also show small-droplet ejection that may adversely affect beam propagation characteristics. The intrusion distance of liquid into the beam lines was determined to be below 10% of the original jet thickness throughout the computational domain (up to 1 m downstream from the nozzle). Recommendations on how to avoid or minimize unwanted hydrodynamic phenomena (surface rippling and droplet ejection) by upstream conditioning and nozzle design are developed for free surface jets in vacuum in the context of a qualitative understanding of the physical mechanisms at play.

The acoustic field of singing humpback whales in the vertical plane

A vertical array of five hydrophones was used to measure the acoustic field of singing humpback whales. Once a singer was located, two swimmers with snorkel gear were deployed to determine the orientation of the whale and to position the boat so that the array could be deployed in front of the whale at a minimum standoff distance of 10 m. The spacing of the hydrophones was 7 m with the deepest hydrophone deployed at depth of 35 m. An 8-channel TASCAM recorder having a bandwidth of 24 kHz was used to record the hydrophone signals. The location of the singer was determined by computing the time of arrival differences between the hydrophone signals. The maximum source level varied between individual units in a song, with values between 180 and 190 dB. The acoustic field determined by considering the relative intensity of higher frequency harmonics in the signals indicate that the sounds are projected in the horizontal direction with the singer’s head canted downward 45 to 60°. High-frequency harmonics extended beyond 24 kHz, suggesting that humpback whales may have an upper frequency limit of hearing as high as 24 kHz.

Optimal Spacing for Casing Centralizers

Summary In the placement of centralizers on casing, it is necessary to integrate information on hole trajectory, casing properties, and centralizer performance. This paper summarizes the basic theory and algorithms for optimizing centralizer spacing based on these considerations. The algorithm predicts the wall forces in a three-dimensional (3D) borehole. Although centralizer placement is important in all wells, it is especially important for highly deviated boreholes and deep, heavy strings. With the detailed approach described here, centralizer placement design gives the operator greater confidence in the prediction of minimum standoff distance for these types of wells. Some examples of field applications are presented. Also, cementing results from field wells support the conclusion that good cement placement is obtained when adequate centralizers are used.

Stand-off distances on a flat flame burner

For a given stand-off distance of a laminar flame on a porous metal burner, it has been shown both experimentally and theoretically that there exists two solutions, a low-speed flame and a high-speed flame. For small enough stand-off distance there is no solution. The minimum stand-off distance is identified as the quasi-steady approximation to the extinction length for flames quenching in flows perpendicular to a heat sink. Measurements of flame speed, maximum flame temperature, and stand-off distance have been correlated for hydrogen, ethylene, and methane flames by a Peclet number dependent only on the ratio of the heat of combustion to the heat loss. The correlation agrees quantitatively with solution of one-dimensional flame equations where a Dirac-delta function models the reaction rate.