For steel products which are subject to moving loads, such as automobile springs, crankshafts, and power takeoff shafts, it is important to know the endurance, or fatigue limit.
Simplified depiction of fatigue or endurance testing.
Specimens are prepared for testing and are subjected to bending as they revolve. In every revolution of the test machine the stress is reversed twice-under load.
With the initial specimen, stress is applied which is far beyond the breaking point. Testing is repeated with different specimens and the applied stress is gradually reduced until a specimen will undergo ten million reversals without breaking. This stress is referred to as the fatigue limit.
The Fatigue Limit is the maximum stress that a material can endure for an infinite number of cycles without breaking. It is also referred to as the Endurance Limit.
Ten million cycles is the engineering community’s testing approximation for infinite.
Image source: Steelways chart dated 1955 on steel testing from my personal archive.
One of the benefits of staying current on professional social media sites is the chance to find some new insights and people with great ideas.
I found this gem on Medical Product Device Development Network on LinkedIn today, and just had to share.
Our thanks to Mike Shipulski for the thought leadership about our contribution as engineers to our firms’ profitability.
You know you're committed to engineering when...
Here’s what Mike had to say about the contributions of engineers:
“We all want to increase profits, but sometimes we get caught in the details and miss the big picture:
Profit = (Price – Cost) x Volume.
“It’s a simple formula, but it provides a framework to focus on fundamentals. While all parts of the organization contribute to profit in their own way, engineering’s work has a surprisingly broad impact on the equation.
“The market sets price, but engineering creates function, and improved function increases the price the market will pay. Design the product to do more, and do it better, and customers will pay more. What’s missing for engineering is an objective measure of what is good to the customer.”
The US has a shortage of engineers, a fact that certainly can be recognized as hindering competitiveness in a world focused on technological innovation.
The President’s Job Council, launched a private sector initiative called 10,000 Engineers, to address the stagnating graduation rate of engineers in U.S. Colleges.
Paul Otellini PCJC Champion for 10,000 Engineers
Employer surveys we have seen indicate that science and engineering positions are the hardest jobs to fill.
In fact, it has been stated that there are three vacancies for every engineer currently graduating in the U.S.
Headed by Paul Otellini of Intel, the 10,000 Engineers program has already signed up 60 companies pledging to double their engineering internships in 2012. Nothing like a little time on task to build commitment to our exciting field of engineering. The internships represent an investment of about $70 million by the companies onboard.
Top Engineering universities are also developing a “Tech Standard Seal of Excellence” to recognize schools with the highest retention rates. (If you measure it- you can change the behavior.) The leading schools currently have very strong mentoring programs, examples for other schools to adopt.
The issue with engineering graduation rates turns out to be related to failure to retain aspiring students in university. Thirty five percent of students enrolled in science, math, and engineering programs leave them after the first year.
American engineers drive the innovations and technologies that improve our quality of life competitiveness and raise our standard of living. The PCJC’s 10,000 Engineers program is one way that the private sector has stepped up to help meet the challenge of having sufficient pool of engineering talent so that there will be new developments for our industry to make.
It is commonly held knowledge by most people that alloy steel is “stronger” or “better” somehow than “ordinary steel.” What makes a steel “alloy steel?” What makes alloy steel “different?”
Chromium, molybdenum, and vanadium are the alloying elements in H 13 tool steel
Alloy Steel
Steel is classified as an alloy steel when the maximum content of manganese exceeds 1.65%; silicon exceeds 0.5%; copper exceeds 0.6%, or in which a definite range or minimum quantity of the following elements are specified:aluminum, boron, chromium (up to 3.99%), cobalt, columbium, molybdenum, nickel, titanium, tungsten, vanadium, zirconium.
These elements alter the steel’s response to heat treatment, resulting in a wide range of possible microstructures and mechanical properties.
Alloying Elements
Alloying elements are always metallic- thus sulfur, phosphorus, carbon and nitrogen are NOT alloying elements.
Alloying elements are added to the steel for the purpose of increasing resistance to corrosion or chemical attack, improve hardness, improve hardenability, or to alter strength.
While the carbon content of steel is the best predictor of its properties, alloying elements are the ingredients that give a particular composition its own particular set of properties.
Key commercial takeaway
Alloying elements typically do not alter the properties of the steel until heat treated. So if someone is purchasing alloy steel and the application does not call for a heat treatment, further inquiry into why they are paying extra for alloy steel is in order.
” The majority of the health outcomes reviewed by the committee were placed into the category of inadequate/insufficient evidence to determine whether an association exists, which means that the studies were too few in number, limited in quality, inconsistent, or inconclusive in results to make an informed assessment. It also means that such an association cannot be ruled out. For diseases and disorders in this category, the committee has concluded that the epidemiologic studies cannot tell us whether exposure to the chemicals is associated with the disease or not.”
Regarding those cases where the evidence was suggestive of an association the National Academy’s report had this to say:
“The strongest evidence was in the category of limited/suggestive of an association, which means that there is some evidence that people who were exposed to TCE or PCE were more likely to have the disease or disorder but that the studies were either few in number or had important limitations. In many cases, the studies could not separate out the effects of individual chemicals because the people were exposed to mixtures. Some of these studies were of highly exposed groups of workers where detection of effects would be expected if present. Such studies might reach conclusions about solvents in general but not about TCE or PCE specifically. For diseases and disorders where the evidence is limited/suggestive of an association, the committee has concluded that the epidemiologic studies give some reason to be concerned that sufficiently high levels of the chemical may cause the disease, but the studies do not provide strong evidence that they actually do so. “
In the EPA’s just released Integrated Risk Information System final risk assessment for trichloroethylene, they ignore the National Academy of Science’s expert opinions on the science of Trichloroethylene. “The studies do not provide strong evidence...”
In the EPA’s latest IRIS assessment, EPA characterizes TCE as “carcinogenic to humans and a human noncancer health hazard.”
EPA 's Science
They state that “TCE is characterized as “carcinogenic to humans” by all routes of exposure. This conclusion is based on convincing evidence of a causal association between TCE exposure in humans and kidney cancer.”
According to National Academy of Science “the studies do not provide strong evidence.”
National Academy’s “No strong evidence” is EPA’s “Convincing evidence of a causal association.”
We wonder why the EPA decided not to heed the National Academy of Science-‘s findings- they were good enough for the Dept. of Navy and the Marine Corps?
We wonder what are the criteria that help EPA to decide when to believe the National Academy of Science and when not?
We wonder why EPA failed to take into account comments by the public and other government agencies when creating this assessment?
We wonder why evidence the National Academy of Sciences characterized as “limited or suggestive of an association” became “convincing” to the EPA?
We wonder is this just another regulatory effort to curtail manufacturing jobs in the United States?
“Manufacturing continued its growth in September as the PMI registered 51.6 percent, an increase of 1 percentage point when compared to August’s reading of 50.6 percent. A reading above 50 percent indicates that the manufacturing economy is generally expanding; below 50 percent indicates that it is generally contracting.”- September 2011 ISM Report.
The view in the marketplace for precision machined products is somewhat less clear.
Precision Machining is an important sector of Fabricated Metals Industry.
Here is a look at the ISM indicators for Fabricated Metals Manufacturing in September.
(Precision machining is a component of Fabricated Metals Manufacturing- the Fab Metal data reflects our machining industries.)
The ISM September 2011 data for Fabricated Metal Manufacturing shows:
New Orders- Growth
Production- Increase
Employment- Decrease
Deliveries- Faster
Inventories- Decrease
Customer’s Inventories- Too High
Prices- Fab Metals is only industry reporting lower prices (as well as higher prices)
Order Backlog- Increase
New Exports- Increase
Imports of Materials- Increase
It may not feel like Christmas, but only two of the above ten indicators (Customer’s Inventories and Employment) were negative for Fab Metals and Precision Machining.
Ford’s volume January – September was up 11.0 %, from 1,419,098 last year to 1,575,699.
GM’s volume January to September was up 16.3% from 1,634,884 a year ago to 1,902,150 by end of September 2011.
The light vehicle market is one of the markets most heavily served by PMPA member shops, and the Big Three mentioned above are particularly important indicators for our industry:
64 % of US production was from these three companies through September.
FYI recent SAAR:
2007- 16.1 million
2008- 13.8 million
2009- 11.9 million
2010- 11.55 million
This year’s additional 1.2 million is helping to keep many precision machining shops busy.
It is well known that centerless grinding processes allow parts to be held to tighter dimensional tolerances, achieve smoother surface finishes, and hold high degrees of straightness.
Cincinnati is the legacy technology.
Beyond these obvious advantages, all centerless grinding processes offer the following 5 Not So Obvious Advantages:
The grinding process is essentially continuous, because the loading time, when compared to grinding between centers, is exceedingly small.
The work is rigidly supported directly under the grinding cut as well as for the full length of the cut. This means that no deflection takes place during the grinding operation, permitting heavier passes than grinding between centers.
No axial thrust is imposed on the work while grinding. The absence of end pressure makes it possible to grind long pieces of brittle materials and to grind easily distorted parts.
Because the error of centering is eliminated, a true floating condition exists during the grinding process. This results in less stock needed and longer wheel life / yield.
Large quantities of smaller size work can be automatically ground by means of a magazine, gravity chute, or hopper feeder attachments, depending on the shape of the workpiece.
A few final thoughts: The degree of error in the centerless grinding process (setup or compensating for wheel wear) is reduced by half, since stock removal is measured on the diameter rather than the radius. Centerless grinding is a mature process, with few wear surfaces in the machine, and automatic lubrication, making maintenance a small part of the total cost of this process.
