In recent years, there is a rapid increase in the application of perforated steel rib shear connectors in steel and concrete composite structures. The connectors must not only ensure shear transfer but also sufficient uplift resistance. The shear behavior of connectors has been extensively investigated. However, studies on uplift resistance are lacking so far.
Therefore, three push-out test specimens were tested to investigate the shear and tension behavior of perforated L-shaped and plain steel rib shear connectors. The failure modes of connectors were analyzed, and analytical models for the determination of uplift resistance were derived based on test results. The results showed that the ductility of perforated steel rib shear connectors under uplift force was smaller than that under shear force, and more severe concrete damage surrounding the rib and larger bending deformation of transverse steel bar was observed.
The rib flange of L-shaped perforated rib has a significant contribution to the uplift resistance. It was suggested to increase the rib height of L-shaped rib to avoid the horizontal crack at the height of the rib flange.
The validity of the proposed analytical models was confirmed by comparing the failure modes and capacities of specimens. In steel and concrete composite structures, various types of shear connectors, such as headed stud shear connector [ 1 ] and perforated steel rib shear connector [ 2 ], are arranged to ensure the composite action between the steel and concrete components.
A perforated steel rib shear connector is a thin steel plate with a number of uniformly spaced holes. After the holes in the perforated rib are filled with concrete, the concrete dowel can resist longitudinal shear and prevent uplift separation between steel and concrete components [ 2 — 5 ].Is Gravity An Illusion?
Though the headed stud shear connector is still the most widely used shear connector, there is an increase in applications of perforated steel rib shear connectors in the composite structures [ 5 — 9 ], owing to their ease of manufacture, excellent load bearing and deformation properties, superior antifatigue performance, and usefulness in slender concrete slabs [ 10 ].
In the literature, the shear behavior of perforated steel rib shear connectors has been studied extensively [ 41112 ] since the earlier research work of Leonhardt et al. The research studies on perforated steel rib shear connectors have shown that the shear behavior is significantly influenced by a number of parameters, including the hole diameter, the number of holes, the compressive strength of concrete, the thickness, length and height of the steel plate, the configuration of transverse steel bar in the hole, and the dimension of concrete slab [ 4 ].
Besides the traditional perforated steel rib with closed recesses, rib connectors with open recesses have developed in recent times.
For the rib connectors with open puzzle-shaped geometry, intense research for the assessment of the shear behavior of rib shear connectors was performed in [ 1314 ] for steel failure, in [ 15 — 17 ] for concrete failure, and in [ 18 ] for fatigue failure. These experimental and theoretical studies led to the development of design principles for puzzle-shaped rib shear connectors under shear forces.
With the increase of composite structures and the widespread use of perforated steel rib shear connectors, it is becoming more common for connectors to be subjected to uplift forces. The behavior of composite structures would be significantly affected by the performance of perforated steel rib shear connectors under uplift forces.A failure mode is the manner in which a system fails, or the manner by which a failure is observed.
So, it is not the same as the cause of the failure, but it describes the way a failure occurs. There are three kinds of failure modes: conceptual, technological and organizational. This text deals with technological failure modes only, and concentrates on embedded control systems. This chapter is very relevant for the embedded systems designer because such systems often work without human supervision and at places where human correction of the failure are expensive to execute.
Therefore, the designers should pay extra attention to what could go wrong in their system i. It is obvious that it is way better to avoid failures than to repair them, and that simple designs are easier in this respect than complex systems; however, making simple designs is still a form of engineering art, and not yet a structured engineering discipline.
Also keep in mind that many failures will not be detected by testing. Technological failure modes in embedded systems can be divided into two main groups: hardware failure modes and software failure modes; the toughest failures to prevent however, are those caused by subtle interactions between hardware and software. Some failures are not caused by hardware or software, but are caused on the system level. Due to the increasing capabilities and functionality of embedded systems, it is difficult to prevent or sometimes even detect failure modes.
One way to ensure reliability is extensive testing using techniques such as probabilistic reliability modeling. One of the problems with these techniques is that they are only used in the late stage of development.
It is better to design quality and reliability in, in the early stages of development. To detect failures in the design process it is important to perform different tests on the system especially on the software at the beginning of the design.
But tests are often expensive and they also should provide the correct information: the usability of test results depend on the quality of the test. So it is not always easy to come up with an appropriate test. Dynamic analysis in the software world is the testing and evaluation of software by executing programs on a processor.
An example of a dynamic analysis on hardware could be vibration and stress analysis. These days engineers have developed a static analysis for software, which is test-free: no specific tests need to be developed and the software can be checked for flaws without having to execute the program.
There are a number of possibilities to reduce the chance of failure occurrences. But some failures need to be treated more urgent than others. At first one should look at the frequency with which a systems fails, this is called the failure rate of a system. It is desired that systems don't fail, but if a failure is very rare it is often not necessary to take steps. Another aspect of a failure mode is its severity. An electrical appliance that short-circuits can be life-threatening, whereas the jamming of a valve in vending machine is less life-threatening.
Despite all the effort an engineer can put into designing a system that doesn't fail, failures will always occur. For example: an average cell phone these days contains as much as 2 million lines of software code. It is very likely that in one of those lines a fault is introduced. Systems are getting even more complex. For instance: that same cell phone is expected to have as much as 10 million lines of code in 10 years. Therefore, a design should be more robust.
Take for example again the jamming of a valve of the vending machine: the machine can light all its LEDs to signal something is wrong and cease providing soda until it is repaired. Failures are also to be expected when separate systems have to work together, for instance: the different robots in RoboCup. An other example of such a complex system are the robots of professor James McLurkin of MIT who have to perform the Star Wars theme tune together, but every robot can only play some notes.
So they have to cooperate in order to play the entire theme correctly. In some cases, it may therefore be more cost effective to not investigate in more trustworthy systems but to pay the failure costs.Colleague's E-mail is Invalid. Your message has been successfully sent to your colleague. Save my selection. Le, David, H. Clinical Orthopaedics and Related Research neither advocates nor endorses the use of any treatment, drug, or device.
Readers are encouraged to always seek additional information, including FDA approval status, of any drug or device before clinical use. Each author certifies that his or her institution approved the human protocol of this investigation, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation in the study was obtained.
Historically, polyethylene wear and its sequelae osteolysis, late instability, aseptic loosening were common causes for revision total knee arthroplasty TKA. Recently, polyethylene manufacturing has become more consistent; furthermore, a clearer understanding of the importance of oxidation on polyethylene performance led to packaging of the polyethylene bearings in an inert environment. This improved the quality and consistency of polyethylene used in TKA, raising the question of whether different failure modes now predominate after TKA.
The purpose of this study was to determine the current reasons for 1 early and 2 late failures after TKA at one high-volume arthroplasty center. We reviewed all first-time revision TKAs performed between and at one institution, yielding a group of revision TKAs in patients. Mean age at the time of revision was 64 years SD 10 years.
Mean time to revision was 35 months SD 23 months. Preoperative evaluations, laboratory data, radiographs, and intraoperative findings were used to determine causes for revision. Early failure was defined as revision within 2 years of the index procedure. The primary failure mechanism was determined by the operating surgeon. In contrast to previous studies, wear-related implant failure in TKA was relatively uncommon in this series.
Changes in polyethylene manufacturing, sterilization, and storage may have accounted for some of this difference; however, longer-term followup will be required to verify this finding. Infection, instability, and stiffness represent the most common causes of early and late failure.
Strategies to improve outcomes in TKA should be aimed at infection prophylaxis and treatment, surgical technique, and patient selection. Level III, therapeutic study. See Instructions for Authors for a complete description of levels of evidence. One projection has suggested that bythe number of primary TKAs performed in the United States annually will grow to 3. This increase in demand will represent a major economic burden [ 17 ].
Medicare data estimate a USD 4. Historically, common causes of failure in TKA have included infection, instability, stiffness, and osteolysis secondary to polyethylene wear [ 235689131516 ].
InSharkey et al. In the mids, new manufacturing techniques for polyethylene appeared to have a major impact on implant survivorship.
Tensile Mechanical Properties and Failure Modes of a Basalt Fiber/Epoxy Resin Composite Material
Polyethylene that was gamma-sterilized in air was prone to oxidation, which reduced the resistance of polyethylene to fatigue and thus predisposed it to early mechanical failure [ 4 ]. By the late s, major orthopaedic implant manufacturers began polyethylene sterilization in inert environments. Tibial inserts that were gamma-sterilized in inert environments exhibited improved mechanical properties, including a lower incidence of delamination in the first decade of implantation [ 12 ].
Whether these changes in manufacturing processes have resulted in a shift in the dominant failure modes after contemporary primary TKA which may well be different now than they were at the time of Sharkey et al's work in [ 13 ] is not known. However, to improve patient health and minimize economic burden, future research must identify the leading causes of TKA failures to help guide our efforts to improve survivorship.Check out our lug calculator based on the methodology described here.
Analysis of a lug is deceptively complex since there are several simultaneous, interacting failure modes. These failure modes are associated with different areas of the lug, as illustrated in the figure below Note: Figure not to scale :.
The failure modes for the lug are listed below. The numbers correspond with the labeled sections from the above figure:. This method is based on first principles as well as on the simplified method outlined in Bruhn and involves making simplifying assumptions about the nature of the failure. While it is relatively easy to perform, it only gives an approximate determination of the adequacy of the lug and should not be employed for critical structure.
A factor of safety is calculated for each of the failure modes, and as long as each factor of safety is acceptable then the lug can be considered to pass.
The figure below shows the lug in blue and the pin in green. Try our lug calculator based on the methodology described here. Tension failure across the net section occurs over the cross-section highlighted in red in the figure below:. The ultimate tensile load is the load that would result in tensile failure across the net section, and is given by:. The equation above assumes a uniform tensile stress over the cross-section.
In reality there will be a stress concentration due to the flow of stress around the hole. A simple and conservative approach is to calculate the length of a single shear plane as:.
If it is desired to account for a slightly longer shear plane, it is common practice to consider a 40 degree line extending from the center of the shear pin. At the point where that 40 degree line intersects the pin hole, extend the shear plane horizontally to the outer edge of the lug. In this case, L sp is calculated as:. This loss is calculated as:. Note that if the lug end is flat then r is infinity and Z is zero.Oper Dent 1 March ; 40 2 : — Thirty extracted human permanent maxillary molars were endodontically treated.
Standardized preparations were done with 2-mm intracoronal extensions of the endocrowns into the pulp chamber. A compressive load was applied at 35 degrees to long axis of the teeth using a universal testing machine until failure.
Failure load was recorded, and specimens were examined under a stereomicroscope for modes of failure and microleakage. In conclusion, although using resin nanoceramic blocks for fabrication of endocrowns may result in better fracture resistance and a more favorable fracture mode than other investigated ceramic blocks, more microleakage may be expected with this material.
Restoration of endodontically treated teeth continues to be a challenge in reconstructive dentistry. A common protocol of restoring such teeth has been to build up the tooth with a post and core to aid the retention of an overlying crown. This can be achieved through a direct approach using a prefabricated intraradicular post followed by a direct core material or through an indirect post and core restoration for teeth with more extensive loss of tooth structure.
However, many clinical and laboratory studies have reported that placing a post will contribute to the retention of the core portion of the restoration but may have a weakening effect on the root.
With the increasing popularity of adhesive dentistry, a shift in treatment decisions toward more conservative modalities has been observed, and the need for conventional post and cores has become less clear.
Endocrowns use the available surface of the pulp chamber axial walls as macroretentive resources and adhesive resin cement as a means of micromechanical retention.
Endocrowns are especially indicated in cases of inadequate clinical crown length, insufficient interocclusal space, and extensive loss of dental tissues that do not allow the use of an adequate ferrule.
This approach has shown promising results and comparable short-term survival when compared to post, core, and crown systems. Teeth were sectioned parallel to the occlusal surface at 2 mm above the cementoenamel junction CEJ to remove occlusal tooth structure and to deroof the pulp chamber. Removal of pulp tissues was done with an endodontic reamer, and determination of root canal lengths was done radiographically with endodontic files inserted in the canals.
Root canals were obturated with a thermoplasticized gutta-percha Calamus Dual, Dentsply Maillefer, Woodinville, WA, USA and root canal sealer AH 26 sealer, Dentsply Maillefer according to the manufacturer's instructions, providing a standardized filling procedure.
The teeth were individually fixed in fast-cure acrylic resin Fastray, Harry J. The roots were embedded in resin up to 2 mm below the CEJ simulated bone level. Intracoronal height of the prepared walls was reduced to 2.
A standardized cavity preparation was performed in all teeth limited to removal of undercut areas of the pulp chamber and alignment of its axial walls with an internal taper of degrees using a tapered diamond coated stainless-steel bur with a rounded end GKR, Edenta, Basel, Switzerland held perpendicular to the pulpal floor.
All internal line angles were rounded and smoothed using the same type of bur. The axial walls were prepared from the pulpal side to provide for a standardized cavity wall thickness of 2.Electronic components have a wide range of failure modes. These can be classified in various ways, such as by time or cause.
Failures can be caused by excess temperature, excess current or voltage, ionizing radiationmechanical shock, stress or impact, and many other causes.
In semiconductor devices, problems in the device package may cause failures due to contamination, mechanical stress of the device, or open or short circuits. Failures most commonly occur near the beginning and near the ending of the lifetime of the parts, resulting in the bathtub curve graph of failure rates. Burn-in procedures are used to detect early failures. In semiconductor devices, parasitic structuresirrelevant for normal operation, become important in the context of failures; they can be both a source and protection against failure.
Applications such as aerospace systems, life support systems, telecommunications, railway signals, and computers use great numbers of individual electronic components.
Analysis of the statistical properties of failures can give guidance in designs to establish a given level of reliability. For example, power-handling ability of a resistor may be greatly derated when applied in high-altitude aircraft to obtain adequate service life.
A sudden fail-open fault can cause multiple secondary failures if it is fast and the circuit contains an inductance ; this causes large voltage spikes, which may exceed volts. A broken metallisation on a chip may thus cause secondary overvoltage damage.
The majority of electronic parts failures are packaging -related. Thermal expansion produces mechanical stresses that may cause material fatigueespecially when the thermal expansion coefficients of the materials are different. Humidity and aggressive chemicals can cause corrosion of the packaging materials and leads, potentially breaking them and damaging the inside parts, leading to electrical failure.
Exceeding the allowed environmental temperature range can cause overstressing of wire bonds, thus tearing the connections loose, cracking the semiconductor dies, or causing packaging cracks. Humidity and subsequent high temperature heating may also cause cracking, as may mechanical damage or shock.
During encapsulation, bonding wires can be severed, shorted, or touch the chip die, usually at the edge.
Dies can crack due to mechanical overstress or thermal shock; defects introduced during processing, like scribing, can develop into fractures. Lead frames may contain excessive material or burrs, causing shorts. Ionic contaminants like alkali metals and halogens can migrate from the packaging materials to the semiconductor dies, causing corrosion or parameter deterioration.
Glass-metal seals commonly fail by forming radial cracks that originate at the pin-glass interface and permeate outwards; other causes include a weak oxide layer on the interface and poor formation of a glass meniscus around the pin. Various gases may be present in the package cavity, either as impurities trapped during manufacturing, outgassing of the materials used, or chemical reactions, as is when the packaging material gets overheated the products are often ionic and facilitate corrosion with delayed failure.
To detect this, helium is often in the inert atmosphere inside the packaging as a tracer gas to detect leaks during testing. Carbon dioxide and hydrogen may form from organic materials, moisture is outgassed by polymers and amine-cured epoxies outgas ammonia.
Formation of cracks and intermetallic growth in die attachments may lead to formation of voids and delamination, impairing heat transfer from the chip die to the substrate and heatsink and causing a thermal failure. As some semiconductors like silicon and gallium arsenide are infrared-transparent, infrared microscopy can check the integrity of die bonding and under-die structures. Red phosphorusused as a charring-promoter flame retardantfacilitates silver migration when present in packaging.
It is normally coated with aluminium hydroxide ; if the coating is incomplete, the phosphorus particles oxidize to the highly hygroscopic phosphorus pentoxidewhich reacts with moisture to phosphoric acid. This is a corrosive electrolyte that in the presence of electric fields facilitates dissolution and migration of silver, short-circuiting adjacent packaging pins, lead frame leads, tie bars, chip mount structures, and chip pads.
The silver bridge may be interrupted by thermal expansion of the package; thus, disappearance of the shorting when the chip is heated and its reappearance after cooling is an indication of this problem. Electrical contacts exhibit ubiquitous contact resistancethe magnitude of which is governed by surface structure and the composition of surface layers.
Soldered joints can fail in many ways like electromigration and formation of brittle intermetallic layers. Some failures show only at extreme joint temperatures, hindering troubleshooting.
Thermal expansion mismatch between the printed circuit board material and its packaging strains the part-to-board bonds; while leaded parts can absorb the strain by bending, leadless parts rely on the solder to absorb stresses.
Thermal cycling may lead to fatigue cracking of the solder joints, especially with elastic solders; various approaches are used to mitigate such incidents. Loose particles, like bonding wire and weld flash, can form in the device cavity and migrate inside the packaging, causing often intermittent and shock-sensitive shorts.X-ray tubes are a proven, cost effective way to produce X-radiation useful in the medical, inspection and scientific fields.
For over years X-ray tubes have made advances owing to new applications, materials, processing equipment and design. Today two types of tubes dominate: rotating anode tubes used primarily for medical purposes from 25 kilovolts kV to kV, and stationary anode tubes used in the inspection industry from 25 kV to over kV with some in the million volt range. Stationary anode tubes typically operate at milliamperes in nearly continuous duty and can be on for many hours at a time.
Rotating anode tubes operate in excess of milliamperes but are used primarily in a pulsed mode of about 1 millisecond to 10 seconds. This factor limits the useful life of the X-ray tube. Many scientific disciplines are required and must be controlled to produce a quality product. The integration and control of the X-ray tube and generator is critical to producing anticipated technical results and long tube life.
Embedded Control Systems Design/Failure modes and prevention
X-ray tubes age and have a limited life because the characteristics and materials used begin a gradual degradation and are consumed so that performance gradually decreases until they no longer perform satisfactory.
Normal Filament Burn Out: The electron beam in an X-ray tube is supplied by a tungsten filament which has been used since the inception of electron tubes and also in incandescent light bulbs.
Despite experimentation with other emitters: dispenser cathodes, Lanthanum and Cerium hexaboride, thorium and rhenium doped tungsten, pure tungsten has remained the best filament material. The filament is made from wire which is wound into a helix and inserted into a cup which acts as a focusing element to form the necessary rectangular electron beam.
The helix serves to strengthen the filament and provides increased surface area to maximize electron emission. Tungsten wire is readily available and processed into useable forms. The wire is relatively strong, rugged and keeps its shape when stresses such as vibration and shock are controlled.
X-ray tube manufacturers stabilize and strengthen the filaments with a process called recrystallization. This changes the raw fibrous wire microstructure into one which the crystal structure has a length to diameter ratio in the range of 3 to 6. Recrystallization is accomplished by heating the wire very rapidly to about Celsius in a few seconds and holding it there for a very short time. A common parameter for filaments is the filament life.
When hot tungsten slowly evaporates from its surface, the higher the temperature the greater the evaporation rate. Hot spots evaporate tungsten more readily and the wire thins more at these locations, ultimately burning open. The higher the filament temperature the more the tungsten grains grow with time and the quicker the notching progresses.
Additionally if high inrush currents are allowed with a cold filament this accelerates burn out by overheating the thinned spots. This represents a reduction of 5. Wilson, Journal of Applied Physics, vol. Accelerated Filament Burn Out: X-ray tube characteristics are affected by several factors including: tube current, tube voltage, anode to cathode spacing, target angle and the focal spot size electron beam size.
Only the anode to cathode high voltage and the filament current temperature determines the tube emission. The emission is governed by the Richardson-Duschman equation which is very dependent on filament temperature; the higher the temperature, the more emission. The filament in a tube runs hotter when more tube current is demanded from the tube at a fixed voltage or when more tube current is demanded but the tube runs at a lower voltage.
Failure of electronic components
For example two cases are compared for a stationary anode tube. First: a tube operating at kV 1 milliampere mAcompared to 5 mA. In this tube the filament is calculated to run about degrees Kelvin, compared to degrees Kelvin at 5 mA.
The degree increase produces an evaporation rate 21 times as much for the 5 milliampere operation compared to 1 mA. XX No. Second, for the same tube operated at 40 kV 5 mA compared to kV and 1 mA the temperatures are K and K respectively which reduces life by a factor of about 43 times. Interestingly, a relatively small decrease in life is experienced with a low tube current when the tube voltage is reduced; for example kV vs.
This shows that tube current increases produced by filament temperature increases are much more important than tube voltage changes. Individual tube types as well as individual tubes of a single type will vary from these examples. Filament failures due to burn-out are caused by high operating temperatures; the higher the temperature, the sooner the filament burns open.
Tungsten evaporates from the filament surface but in a non-uniform way, so hot spots are formed which evaporate more rapidly.