Helicopter Airframe Fatigue Spectra Truncation and Verification

2014 ◽  
Vol 891-892 ◽  
pp. 714-719 ◽  
Author(s):  
John Vine ◽  
Luther Krake ◽  
Beau Krieg
Keyword(s):  
Fatigue Damage ◽  
Fatigue Cracking ◽  
Rotor Blades ◽  
Test Duration ◽  
Large Numbers ◽  
The Us ◽  
Naval Air Systems Command ◽  
Truncation Techniques ◽  
Research And Design ◽  
Improved Methods

Helicopter airframe fatigue cracking is a cause of significant and growing cost of ownership and operational readiness concerns for the operators of (primarily) metallic airframe helicopters. Airframe fatigue has often had relatively low priority for helicopters, with research and design concentrated on the fatigue of flight critical rotating structural components such as rotor blades and pitch links. The Australian Defence Science and Technology Organisation (DSTO) and Naval Air Systems Command (NAVAIR) of the US Navy are collaborating to develop improved methods and technologies that can be used to assess the fatigue damage accrued by ageing helicopter airframes. The flight load sequences, or fatigue spectra, experienced by a helicopter airframe in its lifetime contain many billions of load cycles due to rotor revolutions. The application of spectra containing such vast numbers of load cycles is often impractical for reasons of test duration and cost, therefore spectra simplification techniques must be employed. To this end, truncation is a technique that is used to eliminate non-or lesser-damaging load cycles, producing spectra equivalent in terms of theoretical fatigue damage but with substantially fewer load cycles. This paper describes several truncation techniques that have recently been developed at DSTO specifically to deal with the very large numbers of load cycles that are characteristic of helicopter airframe fatigue spectra. These techniques, which include both sequence and frequency based approaches, feature tunable levels of truncation and allow for large reductions in numbers of turning points while maintaining high-fidelity and realistic fatigue spectra. Also detailed are preliminary results from a comprehensive coupon test program, which DSTO is using to experimentally verify that truncated and un-truncated spectra are approximately equivalent in terms of the fatigue damage that they produce.

Helicopter Airframe Fatigue Spectra Generation

2014 ◽  
Vol 891-892 ◽  
pp. 720-725 ◽  
Author(s):  
Luther Krake
Keyword(s):  
Fatigue Cracking ◽  
Rotor Blades ◽  
Certification Tests ◽  
The Us ◽  
Modes Of Vibration ◽  
Flight Loads ◽  
Naval Air Systems Command ◽  
Efficiency Test ◽  
Research And Design ◽  
Improved Methods

Helicopter airframe fatigue cracking is a cause of significant and growing cost of ownership and operational readiness concerns for the operators of (primarily) metallic airframe helicopters. Airframe fatigue has often had relatively low priority for helicopters, with research and design concentrated on the fatigue of flight critical rotating structural components such as rotor blades and pitch links. The Australian Defence Science and Technology Organisation (DSTO) and the US Naval Air Systems Command are collaborating to develop improved methods and technologies that can be used to assess the fatigue damage endured by ageing helicopter airframes. The flight load sequencesor fatigue spectraexperienced by a helicopter airframe in its lifetime contain many billions of load cycles due to rotor revolutions. Fatigue spectra developed for helicopter airframe certification tests are heavily simplified for reasons such as computational efficiency, test practicality and cost. Real airframe fatigue spectra are likely to be influenced by the modes of vibration that might be present on the airframe, the attenuation of the vibratory loading that is introduced at the main and tail rotors and the relative magnitudes and influences of both quasi-static (manoeuvre induced) and vibratory loading. To better capture such complexity, more realistic, higher fidelity fatigue spectra are required. Fatigue spectra generation involves creating realistic flight-by-flight sequences of flight conditions and assigning high-fidelity flight loads data to those sequences. This paper details DSTOs development of a novel computer-automated process which pseudo-randomly generates realistic sequences of flight conditions to match a known or assumed usage spectrum.

Reluctant Cold Warriors

2019 ◽  
Author(s):  
Vladimir Kontorovich
Keyword(s):  
Cold War ◽  
National Security ◽  
Soviet Economy ◽  
Accurate Analysis ◽  
Policy Makers ◽  
Large Numbers ◽  
The Us ◽  
Comprehensive Survey ◽  
The Cold War ◽  
The Military

The academic study of the Soviet economy in the US was created to help fight the Cold War, part of a broader mobilization of the social sciences for national security needs. The Soviet strategic challenge rested on the ability of its economy to produce large numbers of sophisticated weapons. The military sector was the dominant part of the economy, and the most successful one. However, a comprehensive survey of scholarship on the Soviet economy from 1948-1991 shows that it paid little attention to the military sector, compared to other less important parts of the economy. Soviet secrecy does not explain this pattern of neglect. Western scholars developed strained civilian interpretations for several aspects of the economy which the Soviets themselves acknowledged to have military significance. A close reading of the economic literature, combined with insights from other disciplines, suggest three complementary explanations for civilianization of the Soviet economy. Soviet studies was a peripheral field in economics, and its practitioners sought recognition by pursuing the agenda of the mainstream discipline, however ill-fitting their subject. The Soviet economy was supposed to be about socialism, and the military sector appeared to be unrelated to that. By stressing the militarization, one risked being viewed as a Cold War monger. The conflict identified in this book between the incentives of academia and the demands of policy makers (to say nothing of accurate analysis) has broad relevance for national security uses of social science.

Explosive Removal of Concrete From Reinforced Walls

2007 ◽  
Author(s):  
Denis D. Rickman ◽  
John Q. Ehrgott ◽  
Stephen A. Akers ◽  
Jon E. Windham ◽  
Dennis W. Moore
Keyword(s):  
Explosive Charge ◽  
Research Effort ◽  
Us Army ◽  
Steel Reinforced Concrete ◽  
The Past ◽  
The Us ◽  
Development Center ◽  
The Relationship ◽  
Improved Methods ◽  
Combat Environment

During the past several years, the US Army has focused considerable attention toward developing improved methods for breaching walls in the urban combat environment. A major thrust area is centered on finding improved methods to breach the toughest wall type that Army units are likely to face: a double (steel) reinforced concrete (RC) wall. One impediment to this effort is that the relationship between the contact explosive charge configuration and the quantity of concrete removed has not been thoroughly understood. The U.S. Army Engineer Research and Development Center has conducted a research effort to better define the effectiveness of various explosive charge configurations in breaching RC walls. This paper presents a discussion of results from this research.

Informal and ubiquitous: Colonias, premature subdivisions and other unplanned suburbs on America’s urban fringe

Urban Studies ◽  
2018 ◽  
Vol 56 (4) ◽  
pp. 722-740 ◽  
Author(s):  
Noah J Durst
Keyword(s):  
Federal Government ◽  
Low Income ◽  
Land Development ◽  
Poor Quality ◽  
Urban Fringe ◽  
Border Region ◽  
Diverse Populations ◽  
Urban Informality ◽  
Large Numbers ◽  
The Us

Along the US border with Mexico there are thousands of communities designated by the federal government as colonias, a name that highlights the large numbers of low-income, Hispanic immigrants that live in these communities. These subdivisions have been studied extensively in recent years, often using insights from the concept of urban informality. This research has highlighted the challenges posed by exploitative land sales practices, poor-quality or non-existent infrastructure and poor-quality housing in these communities. However, similar informal subdivisions exist along the urban fringe elsewhere across the US, though they are not designated as colonias by the federal government and scholars rarely consider their similarities to colonias in the border region. This study uses data on Census Designated Places from the American Community Survey, satellite imagery and county property records to examine the extent and nature of these subdivisions. The results illustrate that informal land development of the sort described here is not restricted only to the border region, to immigrant enclaves or to Hispanic communities. Instead, it is demonstrated that informal subdivisions exist in large numbers across Southern and Western states and, though their numbers are smaller, they are present even in the Midwest and Northeast. Moreover, these subdivisions are home to diverse populations and they provide important benefits such as expanded opportunities of homeownership for minorities and the poor.

Computing Hardware

2018 ◽  
Author(s):  
James A. Anderson
Keyword(s):  
World War Ii ◽  
Analog Computer ◽  
First Century ◽  
World War ◽  
Slide Rule ◽  
Fire Control ◽  
Large Numbers ◽  
The Us ◽  
Control Computer ◽  
Device Properties

Chapter 2 presents a kind of computation currently unfamiliar to most, the analog computer. Fifty years ago, they were considered viable competitors to the newer digital computer. Analog computers compute by the use of physical analogs, using, for example, voltages, currents, or shaft positions to represent numbers. They compute using the device properties, not logic. Examples include the balance, a simple device known for millennia; the “Antikythera mechanism,” a complex astronomical calculator from the first century BC; the slide rule; the US Navy’s Mark I fire control computer used for much of the 20th century to aim naval gunfire; and electronic analog computers built in large numbers after World War II. Analog computers can have advantages in ruggedness, simplicity, and reliability but lack the flexibility of digital computers.

Mechanistic–empirical damage analysis and impacts of reduced tire pressure on thaw weakened flexible pavements using the AI and MEPDG models

2012 ◽  
Vol 39 (7) ◽  
pp. 812-823
Author(s):  
Leonnie Kavanagh ◽  
Ahmed Shalaby
Keyword(s):  
Fatigue Damage ◽  
Flexible Pavements ◽  
Fatigue Cracking ◽  
Flexible Pavement ◽  
T Test ◽  
Pavement Design ◽  
Damage Analysis ◽  
Confidence Limits ◽  
Tire Pressure ◽  
Design Guide

A damage analysis was conducted on a spring weight restricted flexible pavement to quantify the effects of reduced tire pressure on pavement life and to compare the damage predictions from the Asphalt Institute (AI) and the Mechanistic Empirical Pavement Design Guide (MEPDG) models. The models were used to predict the number of repetitions to fatigue and rutting failure at three maximum loads and at high and low tire pressures. Based on the results, the AI and MEPDG predictions were statistically different for both fatigue cracking and rutting damage, based on the t-test at 95% confidence limits. The AI model predicted 31% lower fatigue damage than the MEPDG, but 56% higher rutting damage. However, both models produced similar trends in predicting the relative effects of reduced tire pressure and load levels on pavement life. The methodology and results of the analysis are presented in this paper.

Correlation of a Sinusoidal Sweep Test To Field Random Vibration

1997 ◽  
Vol 40 (6) ◽  
pp. 35-41
Author(s):  
Jimmy Hu
Keyword(s):  
Structural Properties ◽  
Fatigue Damage ◽  
Random Vibration ◽  
Test Duration ◽  
Vibration Level ◽  
Random Load ◽  
Life Goal ◽  
Test Specification ◽  
Measured Field ◽  
Lab Test

This paper presents a method for transferring the measured field random vibration into a sinusoidal sweep test by using the damage equivalence technique. This requires the fatigue damage generated in the sinusoidal sweep to be equivalent to the damage during the desired lifetime in the field operation. Based on this approach, a correlated lab-test specification, including the vibration level and test duration, can be determined according to the field random load input, the desired product life goal of a product, and the material/structural properties. If a generic test specification is required without knowing the material/structural properties, an approximate approach is proposed based on some engineering assumptions. In this paper, the development of a test specification for an automotive bracket is demonstrated as an application example.

US ‘big tech’ and organised workers will clash

2019 ◽  
Keyword(s):  
Support Staff ◽  
Employee Rights ◽  
Content Type ◽  
Labour Unions ◽  
Security Guards ◽  
Gig Economy ◽  
Large Numbers ◽  
The Us

Subject Organised workers and 'big tech'. Significance Given the US big tech’s high margins and large numbers of support staff, labour unions have made some inroads in organising their contract staff such as drivers, security guards and cafeteria workers. Tech companies have also seen increases in employee activism such as walkouts, although this has stopped short of full unionisation drives. Impacts The spread of the gig economy will sharpen political scrutiny of corporate practices on employee rights. Democratic politicians, in particular, will struggle to court both big tech and unions. Firms will partner with the NLRB, where possible, to prevent employees from using internal emails and messaging apps to stage strikes.

Preparation of cell populations with stabilized erythropoietic potential from the primitive streak chick blastodisc: Some implications for control of gastrulation

1978 ◽  
Vol 56 (6) ◽  
pp. 430-439 ◽  
Author(s):  
S. D. Wainwright ◽  
Lillian K. Wainwright
Keyword(s):  
Egg Yolk ◽  
Primitive Streak ◽  
Cell Suspensions ◽  
Erythroid Cells ◽  
High Concentration ◽  
Differentiated Cells ◽  
Viable Cells ◽  
Large Numbers ◽  
Cell Dispersion ◽  
Improved Methods

Improved methods for preparation from primitive streak chick blastodiscs of cell suspensions capable of forming erythroid cells in culture have been developed. When blastodiscs were preincubated with hyaluronidase in the absence of collagenase before cell dispersion and a high concentration of methyl-α-mannoside was present in all media, the yields of cells were some 10-fold higher than those obtained by former procedures. Cell suspensions obtained consisted almost entirely of viable cells, yielded large numbers of free mature erythrocytes in liquid culture, and formed erythroid colonies and bursts in solidified medium. The capacity to form differentiated cells after re sedimentation through Ficoll density gradients was partly stabilized.Addition of egg yolk homogenate to the blastodiscs immediately following treatment with hyaluronidase and to all media used thereafter largely stabilized the capacity to form erythroid cells during re sedimentation through Ficoll density gradients.Possible relevance of observations made during development of the procedures to the control of onset of cell migration in the process of gastrulation is indicated.

scholarly journals A survey of working conditions within biomedical research in the United Kingdom

F1000Research ◽  
2017 ◽  
Vol 6 ◽  
pp. 229
Author(s):  
Nick Riddiford
Keyword(s):  
Biomedical Research ◽  
Online Survey ◽  
Academic Research ◽  
Career Stage ◽  
The United Kingdom ◽  
Large Numbers ◽  
The Us ◽  
Toxic Environment ◽  
The Uk ◽  
The Guardian

Background: Recent articles have presented a bleak view of career prospects in biomedical research in the US. Too many PhDs and postdocs are trained for too few research positions, creating a “holding-tank” of experienced senior postdocs who are unable to get a permanent position. Coupled with relatively low salaries and high levels of pressure to publish in top-tier academic journals, this has created a toxic environment that is perhaps responsible for a recently observed decline in biomedical postdocs in the US, the so-called “postdocalypse”. Methods: To address the gulf of information relating to working habits and attitudes of UK-based academic biomedical researchers, a link to an online survey was included in an article published in the Guardian newspaper. Survey data were collected between 21st March 2016 and 6th November 2016 and analysed to examine discrete profiles for three major career stages: PhD, postdoc and principal investigator. Results: Overall, the data presented here echo trends observed in the US: The 520 UK-based biomedical researchers responding to the survey reported feeling disillusioned with academic research, due to the low chance of getting a permanent position and the long hours required at the bench. Also like the US, large numbers of researchers at each distinct career stage are considering leaving biomedical research altogether. Conclusions: There are several systemic flaws in the academic scientific research machine – for example the continual overproduction of PhDs and the lack of stability in the early-mid stages of a research career - that are slowly being addressed in countries such as the US and Germany. These data suggest that similar flaws also exist in the UK, with a large proportion of respondents concerned about their future in research. To avoid lasting damage to the biomedical research agenda in the UK, addressing such concerns should be a major priority.

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