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Knovel Solutions are the stories of engineers who have used Knovel to solve real life problems.
Every spring season, fans flock to baseball stadiums and cheer for their favorite teams and players. With an average attendance rate of 25,000 fans per game, stadium engineers need to create structures that ensure the safety and comfort of all attendees.
This problem comes from a design engineer working on replacing the sunshade support beams in a baseball stadium.
Knovel Solutions are the stories of engineers who have used Knovel to solve real life problems.
In building commercial aircraft, it is imperative for engineers to be precise in their work. Even the smallest error can become a costly failure. Engineers in the Aerospace industry need reliable sources to find effective design solutions for their projects.
This problem comes from a structural engineer at a leading aerospace company. He used information found on Knovel to fix a defect in the airplane frame caused by improper repair.
Read the rest of this entry »
Knovel Solutions are the stories of engineers who use Knovel to solve real life problems.
This problem comes from a marine engineer. As a part of the modernization plan at the shipyard where he works, the engineer needs to order new welding equipment. He decides to use Knovel to find images about advanced welding technologies suitable for marine applications.
The shipyard uses large volumes of plates and T shapes to make decks, bulkheads, shells and other structural components. As the need for weight and cost reduction grows, T-beams are being manufactured with stronger materials and smaller cross-sections. These thin materials are subject to significant distortion as they are welded. Some estimates place the cost of distortion at 30% of the structural cost of the ship.
The engineer must research processes and equipment for the mechanized welding of T- beams and flat panels with supporting girders in a way that minimizes distortion.
After compiling his data, the engineer will report back with his findings. The report should contain examples of successful implementations of the selected technology in marine applications.
Next Steps:
Research mechanized welding technologies used in marine applications and select the technology that meets the requirements
Report his findings
Researching welding technologies
The engineer starts by searching Knovel for ‘automatic welding’ (Click to run search):
On the search results page, he opens Chapter 9.2.1.2 Automatic Welding with Cored Wires in Ship Construction (6th Edition). The selection (below) states that SAW (Submerged Arc Welding) is the most commonly used welding technology for mechanized welding in shipbuilding.
Browsing further, the engineer reads that LBW (Laser Beam Welding) and HLAW (Hybrid Laser Arc Welding) are new welding techniques applicable for shipbuilding applications.
HLAW is of special interest to the engineer because this technique is recommended for the welding of T- beams and girder-supported flat panels for decks and superstructures to minimize the distortion of metal of moderate thickness. It is also very important that this technology is suitable for a wide range of steels and aluminum alloys.
Learning more about HLAW and application examples:
Now, the task of the engineer is to find out more about the technology, i.e., process parameters (speed of welding, metal grades, range of thicknesses, forms, positions, metal preparation, gaps, etc.), equipment, power consumption, advantages and disadvantages. The engineer searches Knovel for ‘hybrid laser arc welding’ (Click to run search):
On the search results page, he opens Chapter 9.1 Introduction in Failure Mechanisms of Advanced Welding Processes and navigates to pages 219-223 to read more about laser welding and HLAW.
Click here to read the engineer’s findings.
Going back to the search results page, the engineer opens another selection, Hybrid Laser-Arc Welding, to learn more about the implementation of HLAW technology to the welding of high-strength steel, Zn-coated steel, stainless steel, aluminum alloys and even dissimilar metals. He continues to browse this selection and finds a wide range of examples of successful application of HLAW in shipbuilding at shipyards in different European countries.
Finally, at the end of this chapter, he reads:
Searching for welding processes on Knovel, the engineer finds that:
On the basis of information gathered from Knovel, the engineer recommends the implementation of HLAW technology at his shipyard. His next steps are to start contacting suppliers and write the report.
Knovel Solutions are the stories of engineers who have used Knovel to solve real life problems.
FEA (Finite Element Analysis) methods often underestimate the impact of stress concentration on the strength of mechanical components. The example below walks through how stress concentration methodology found on Knovel can be used in the design phase to increase the strength of a mechanical part without FEA.
This common engineering problem comes in the form of a story from a bicycle component manufacturer. The manufacturer recently received a number of claims from customers related to the failure of pedal axles. In order to correct their design, an engineer was brought in to assess the problem and offer a solution.
An engineer was assigned the task of redesigning the axle to reduce stress by 10-15%, which was deemed to be sufficient in preventing failure of the axle.
(Configuration of axle at the point of failure, dimensions in millimeters)
What We Know:
Next Steps:
Researching Designs That Reduce Stress
The engineer starts with a search for ‘stress concentration’ (Click to run search)
Open the Peterson’s Stress Concentration Factors (3rd Edition) and review the table of contents. Chapter 3 of this book is dedicated to concentration factors at shoulder fillets:
(Click to enlarge)
And Section 3.4 Bending contains equations for calculations of stress concentration factors and recommended methods for reduction of stress concentrations.
Method 1: Streamline Fillet
One of these methods involves using a streamline fillet.
Looking through Chapter 3 for more information on streamline fillets, the engineer finds a table with proportions for these fillets (Table 3.1 below).
Unfortunately, the fillet designed according to this table would have increased the diameter of the axle shank to at least (1.475 x 12 mm) + 2 mm = 19.7 mm, where 1.475 is the fillet to axle diameter ratio (see highlighted value in the Table 3.1), 12 mm is the axle diameter, and 2 mm are added to account for a shoulder required to mount the bearing.
Such an increase in the axle diameter is not acceptable because of extra weight and design considerations.
Method 2: Variable Radius Fillet
Another method, suitable for any type of loading (including torsion), is recommended on page 140. It involves a compound radius fillet (also called double radius fillet):
(Click to enlarge)
Design & Testing of Variable Radius Fillet
At this point, the engineer decides to determine if he can reduce stress by using a double radius fillet (see Figure 3.11). He turns to Section 3.5.3 Compound Fillet.
Specifically, he wants to find out if using the radius r2=6 mm and r1=1.4 mm would reduce maximum stresses in the axle.
Two distinct maximum stress concentrations have to be calculated: one for the circumferential line I and another for the circumferential line II.
The drawing of the resulting axle with the diameter at circumferential line I 12 mm and diameter at circumferential line II 13.6 mm is shown in Fig. 2 below:
The chart (click to enlarge) for stress concentration factor for this case is provided on the page 165 of the book:
Since this chart is interactive on Knovel, the engineer uses it to quickly determine stress concentration factors for the axle with modified design:
Using Knovel Graph Digitizer for Chart 3.10 (see picture below), let’s determine stress concentration factors for original condition and for circumferential line I and calculate stress reduction:
(Click to enlarge)
Now let’s determine stress concentration factor for circumferential line II:
The stress concentration factor at this section is obviously higher. However, since the diameter is significantly larger, the nominal stresses are smaller and, as a result, the concentrated stresses are smaller than those for the circumferential line I:
These preliminary calculations have shown that the nominal stresses at the circumferential line II are 68.7% the nominal stresses at the circumferential line I. Thus, the maximum stresses are 88.4% of the maximum stresses at the circumferential line I.
The engineer would like now to verify these calculations because one point was extrapolated outside the range of the chart and therefore could be inaccurate. To calculate, he uses the equations provided at the top of the chart. For the original design with single radius r=2 mm (see Fig. 1):
And then for the double fillet design with radius r2 increased to 6 mm as shown in Fig. 2:
The calculations (click here to see all calculations) demonstrate that replacing a fillet with single radius r = 2 mm with a double radius fillet having r2 = 6 mm decreases the stresses by about 16% which is sufficient to solve the problem.
Alternate Methods
A few more methods of reducing stress concentration are proposed in Section 3.6 Methods of Reducing Stress Concentration at a Shoulder. The most interesting method for the pedal axle is a relief groove.
The advantage of this method is that the configuration of the axle remains the same.
The calculations demonstrate that replacing a fillet with single radius (r = 2 mm) with a double radius fillet (with r2 = 6 mm) decreases the stresses by about 16%, which is sufficient to reduce the stress of the axle to acceptable levels.
Knovel Solutions are the stories of engineers who have used Knovel to solve real life problems.
Because test drilling for oil and gas often occurs in hard to reach areas of the world, the logistics become an important component of planning, and all aspects of the primary materials (drill pipe and cement) chosen must be considered.
In this issue, we are concerned with estimating the weight of the materials to be delivered to the drilling site.
The engineer responsible for logistics at a drilling site needs to calculate the weight of materials to be ordered for a well drilling operation
What We Know:
Next steps:
*To perform the cement calculations, the engineer needs to know slurry yield for an A class cement with recommended water-to-cement ratio and allow for 25% excess of material without taking into account the additives.
Knovel Solutions are the stories of engineers who have used Knovel to solve real life problems.
In this issue, we help to answer a question submitted by an engineer working at one of the world’s leading manufacturers of sustainable industrial floor maintenance equipment. Their products clean high traffic industrial surfaces such as airports, warehouses and even the floors of the White House and Yankee Stadium.
For two weeks, the engineer who submitted this problem researched the best ways to find a solution.
He needed to protect the steel shaft and die-cast aluminum brush hub of a hard floor scrubber machine from failure in a locked-rotor condition. He knew that one method of protection is to design a shaft key that fails before there is any damage to more expensive parts.
His question:
Can a steel key protect the shaft and the brush hub of a floor scrubber from damage?
What We Know:
The shaft of a hard floor scrubber machine is made of steel and has a diameter of 11/16 in. The output torque is 250 in-lbf at 200 rpm. The driven brush hub is made of die-cast aluminum. The destructive shear stress for the shaft material is 32,000 psi, and destructive compressive stress for die-cast aluminum is 24,000 psi.
The questions are:
Finding the recommended dimensions
We start with a search for ‘key size for shaft diameter’. (Click to run search)
And open Table 1, Key Size Versus Shaft Diameter in Machinery’s Handbook (27th Edition) & Guide to Machinery’s Handbook:
From this table, the recommended dimensions of the key are 3/16 × 3/16 in.
Now let’s find the equations for calculation of the torque moment for the shaft and shaft key.
A quick search for ‘shaft key’ retrieves the chapter Design of Transmission Shafting in Machinery’s Handbook (28th Edition) & Guide to Machinery’s Handbook.
There is an equation for calculation of the shaft diameter on page 301:
Using this equation we can calculate the torsion moment corresponding to 80% of the dangerous stress in the shaft.
From Table 1 on page 302, we find that the Kt factor is 1.5 and factor B=1 because the shaft is solid. Opening chapter 17., Design of Shafts and Keys for Power Transmission on page 155, we find equations for the torque moment versus dimensions of the key:
In the equation, “2″ represents the compressive stress of the hub material. It is used because the value is smaller than the destructive stress of the steel.
When we appy the values to the equations, the result is:
As we can see, the torque moment at which the shearing stress in the key is dangerous is greater than the torque at 80% of dangerous compressive stress in the hub — and even greater than the torque at 80% of dangerous shear stress in the shaft. So the steel key of these dimensions will not protect the hub and even the shaft.
Let’s calculate the destructive shearing stress for the material of the key required to protect the hub and the shaft. In order not to damage the shaft and the hub, the torque moment of key shear should not exceed the moment Tc:
Therefore, to protect the shaft and the hub with the key of these dimensions, we have to use a material with a destructive shear stress that is not more than 9,600 psi. The allowable shear stress should not to be less than….
to handle the maximum output torque of 200 lbf-in. We then use Data Search to restrict our results to interactive properties data. Entering the field name shear strength and our value of 9,600 psi,
(Click to enlarge)
we find the interactive table Estimated Minimum Mechanical Properties of Wrought Aluminum Alloys – (engineering units) in the Aluminum Alloy Database.
In this table, we learn that 1060 H16 tempered alloy satisfies our requirements:
(Click to enlarge)
This alloy has an ultimate shear stress of 8,000 psi and a yield shear stress of 6,000 psi, which is higher than 2327 psi, allowable shear stress in the key calculated earlier for 200 lbf-in torque. Hence, this alloy is able to handle output torque of 200 lbf-in safely. Reviewing the properties of this material, we notice that the key thickness has to be increased to prevent failure due to crushing.
Our conclusions:
An engineer needs to design a temperature trigger to be used in a steam control valve. The valve is installed on a live steam line in a tank with water that is being pre-heated from 20 to 80ºC. The pressure of the steam is 2 atm.
Calculating boundary conditions and the thermal expansion coefficient of copper.
What We Know: The main component of the trigger is a 15-mm-long cantilever beam made from copper. It has a rectangular cross section of 1 x 3 mm (depth and width, respectively). It bends due to a temperature difference between the top and the bottom surface of the beam. The engineer has to calculate flexural deformation 2 mm from the free end of the beam. Read the rest of this entry »
An engineer working at a shipyard’s sheet metal fabrication shop has to calculate the maximum bend length for a metal sheet that needs to be bent 90° without bottoming.
What We Know:
The shop has a 30-ton press brake. Two V-dies are available with 2” and 1” openings, respectively. The sheet metal is 1/8″-thick AISI 4130 low-alloy steel. The engineer wants to calculate the bending capacity of the break for both dies in order to figure out the optimal cutting pattern for the sheet metal during fabrication.
After not finding a suitable calculation procedure in the manuals he has at-hand, the engineer turns to Knovel. Read the rest of this entry »
Relief valves protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits.
In this scenario, a bellows pressure relief (PR) valve needs to be sized in line with the mass flow rate for a gas pipeline with natural gas under critical flow conditions, i.e., when total superimposed pressure plus built-up back pressure is equal to or less than the critical flow pressure. An Engineer, a PE and mechanical engineering consultant in Florida, turned to Knovel. Read the rest of this entry »
