Accurate Testing Starts with the Preload

Often when visiting customer sites, our service engineers find machines that have basic setup problems that can have a large effect on the accuracy of test results. A very common problem is testing with poorly preloaded grip locknuts. Placing a specimen under tension also places all items in the load string – grips, grip adapters, load cell, and so on – under tension as well.


Grips Supplied with Locknuts
If the locknut is insufficiently tight, the forces experienced during a test, particularly a cyclic test, can cause backlash in the load string leading to errors in the test data. Before testing, make sure that you preload the load string, using a load greater than the expected maximum load, and tighten the grip locknuts while the load is applied. Read more

Full Fluid Jacket – Liquid Body Armor

Humans have waged war on one another for centuries. Weapons have evolved from sticks and stones through cutting and bludgeoning implements to today’s smart bombs and missiles. But the evolution of the means to protect oneself from the impact of those weapons has not kept pace. However, a new technology combining two advanced materials – Kevlar and shear-thickening fluid – may hold the promise of light, flexible and effective full body armor.

Today’s body armor is a compromise between protection and agility. Most modern body armor comprises many layers of woven Kevlar, sometimes with ceramic plates to give extra protection. Kevlar is an aramidic fiber, which forms hydrogen bonds between its chains of molecules and thus has a very high tensile strength and high toughness. It is five times stronger than steel on an equal weight basis and it already saves countless lives.

Although Kevlar offers vastly increased protection for the wearer, it does have some drawbacks. For effective protection, up to 30 or 40 layers of Kevlar are needed. This many layers, together with additional ceramic plates, make the armor bulky, stiff and heavy, meaning that the wearer cannot move around as easily. Also, body armor does not offer protection for extremities, such as arms, legs or the neck because the number of layers of Kevlar needed to offer sufficient protection would be too stiff and bulky for use as sleeves, trousers, and so on.

A great deal of largely US-military-funded research has taken place over the last few years into combining Kevlar fabric with a shear-thickening fluid. Shear-thickening fluid is an example of a "smart material," a class of materials that can sense and respond to changes in the environment, for example through the application of electricity or magnetism, or to changes in temperature. Shear-thickening fluids increase their viscosity in response to changes in pressure. An example of a fluid under research is ethylene glycol containing suspended nano-particles of silica. Under normal conditions, the particles are weakly bonded to each other and can move around with ease. The shock of an impact strengthens those chemical bonds and the particles lock into place. Once the force from the impact dissipates, the bonds weaken again.

The liquid technology can improve both the performance and the utility of Kevlar fabric. Saturating Kevlar fabric in a shear-thickening fluid causes the fluid molecules that are already bonded with each other to also form weak chemical bonds with the polymer chains of the Kevlar fibers. The weak bonding allows the fabric to remain flexible. When a projectile strikes the fabric, it becomes rigid within two-thousandths of a second, preventing penetration. Furthermore, the reduced flow of the fluids in the liquid armor restricts the motion of the fabric yarns in relation to each other, resulting in an increase in the area over which the impact energy is dispersed. As a result, the material does not distort as much as the standard body armor, which generally extends inwards substantially when a projectile strikes, causing considerable pain and injury. Once the event is over, the fabric returns to its former flexible state.

The mechanical properties of the material are being evaluated using a wide range of tests and test equipment. Drop towers test puncture resistance with knives and icepicks as well as various shapes and sizes of instrumented tups. Load frames are used to test resistance to abrasion, fiber pullout, and tearing. Gas guns are used to fire ballistics such as bullets and shrapnel.

Impregnating Kevlar with a shear-thickening fluid strengthens the fabric to such an extent that improved protection can be achieved with a material that is one-third the thickness of Kevlar alone. Therefore, the body armor can be lighter, more flexible and yet offer greater protection from projectiles, shrapnel and explosive devices – the major causes of injury and death in modern conflicts. Seventy per cent of all non-fatal injuries and sixteen per cent of deaths in a war zone are due to trauma to extremities. Because fewer layers are necessary with the new material, supple armor for arms and legs is now possible. Extremity armor using shear-thickening fluid impregnated Kevlar could significantly reduce the number of injuries in battle as well as saving lives.
Read more

The Burj Khalifa – Cast in Concrete

The Burj Khalifa, the world’s tallest building, has a laundry list of superlatives. Greatest number of stories, highest occupied floor, longest travel distance elevator, world’s highest swimming pool. Perhaps none of these would have been achievable without the great advances that have been made in concrete technology over the past 20 to 30 years.

Until the 1990s, concrete wasn’t a cost-effective solution for the construction of tall buildings – it had limited strength, it was heavy, and fabrication was longer than for steel construction. Generally steel was looked at as the solution for super-tall buildings.
However, there have been significant advances in many aspects of concrete technology with great increases in strength, modulus and durability. High-performance concrete (HPC) mixtures provide a wide range of mechanical and durability properties to meet the design requirements of a structure. Even so, the challenges facing the structural and construction engineers on the Burj Khalifa project have been huge. Most of the Burj Khalifa is a reinforced concrete structure, except for the top, which consists of a structural steel spire with a diagonally braced lateral system. 330,000 m3 (431,600 yd3) of high-performance concrete is used throughout the building.

One of the major requirements for the successful completion of this project was the ability to pump the concrete slurry up to a height of 600 meters (1968 feet) in a short enough time span (around 30 minutes) to ensure the concrete remained workable and retained its high performance properties. Three high-pressure pumps were used at the construction site to lift concrete up to crews working at unprecedented heights.

To decrease construction time, the concrete was designed to be self-consolidating (SCC), meaning a concrete mix that leveled itself solely due to its own weight, with little or no vibration. It spread into place, filled formwork, and packed tightly into even the most congested reinforcement, all without any mechanical vibration.

Great care was necessary to achieve and maintain the desired performance of concrete in this region. The Middle East is not a benign environment for concrete due to the extremely wide range of temperatures experienced throughout the year. The ability to pump and place concrete at high ambient temperature to significant heights while preventing excessive cracking and possible service life issues in the strong drying conditions was vital for the efficient and economic use of HPC. During the summer months, when shade temperatures can exceed 50°C (122°F), the concrete’s water content was almost completely composed of flake ice to achieve the common limit of 32°C (90°F). Whenever possible, and in particular during the hottest months, all pumping of concrete took place at night.

The importance of extensive testing of the concrete could not be overstated. Prior to the construction of the tower, extensive concrete testing and quality control programs were put in place to ensure that all concrete works were done in agreement with all parties involved. These programs started from the early development of the concrete mix design until the completion of all test and verification programs. Five different concrete mixture designs were tested. The testing regimes included, but were not limited to the following:

• Test the mechanical properties of each mixture, including compressive strength, modulus of elasticity, and split tensile strength
• Test and measure the concrete properties (fresh and hardened) before and after pumping
• Test for creep and shrinkage for all mixtures
• Test for water penetration and rapid chloride permeability
• Test the shrinkage of the concrete mixtures
• Pump simulation testing for all concrete mixtures grades up to at least 600 meters (1968 feet)

The Burj Khalifa is the current state-of-the-art in super-tall buildings, exploiting the latest advances in construction materials and methods. The result is a structure that surpasses anything that has been achieved before. Read more

Seeking Your Input .....

We've been blogging and you've been reading, but are you finding what you've expected at the Instron Community?

We're interested in hearing your input on articles to focus on for 2012 - more technical tips, more industry news ..... What do you find beneficial? I've included a poll on the right side of our blog - please take a few moments to fill it out or include your comments below.

Thanks so much and happy holidays! Read more

Liquidmetal – Not Just for Terminators

Materials scientists have been trying for years to discover and develop a product that could be molded into complex shapes with the ease and low expense of plastic while retaining the strength and durability of metal. Recently, a team led by Dr. Jan Schroers, a materials scientist at Yale University and the former Director of Research at Liquidmetal Technologies, has recently developed some metal alloys that can be blow molded like plastics into complex shapes that can't be achieved using regular metal, without sacrificing the strength or durability that metal affords.

Dr. Jan Shroers with metal bottle
Photo courtesy of Dr. Shroers

Liquidmetal is a commercial name for a series of bulk metallic glass (BMG) alloys developed by a CalTech research team and marketed by a firm called Liquidmetal® Technologies. BMG alloys are solid at room temperature, but they become increasingly soft and liquescent at higher temperatures rather than exhibiting a fixed melting point as with a conventional metal.

It’s the atomic structure of a BMG alloy that differentiates it from a conventional metal. The atomic structure of a conventional metal is crystalline, with repeating crystal patterns in planes, and usually containing dislocations, or irregularities, in the structure. The tendency of the crystalline structure to slip and deform under load limits the overall mechanical performance of conventional metals.

The atomic structure of BMG alloys is amorphous, where no discernible patterns exist in the atomic structure. The absence of grain boundaries and dislocations results in a material with a large elastic strain limit and a very high yield strength, close to the theoretical limit. As an example, one zirconium-based BMG alloy exhibits a yield strength of up to 2 GPa and an elastic strain limit of about 2%. BMG alloys also demonstrate excellent corrosion resistance, very high hardness, and excellent anti-wearing characteristics, while also being able to be heat-formed in processes similar to those used with thermoplastics.

Liquidmetal was introduced commercially in 2003 and has been used to manufacture electronic casings, medical devices, jewelry materials, and sporting goods. Die-casting is the main manufacturing process, but it is subject to conflicting demands. The conditions needed to obtain high-quality casts are slow cooling and small temperature gradients. In a die-cast process, the liquid BMG must fill the entire mold cavity while at the same time be cooled fast enough to avoid crystallization. This makes casting of parts with complex geometries difficult.
Schroers claims that the alloys can be blow molded just as cheaply and as easily as plastic. So far his team has created several complex shapes, such as metallic bottles, watch cases, miniature resonators, and biomedical implants that are seamless, twice as strong as steel, and can be molded in less than a minute.

On the tech blog Cult of Mac, Schroers said it is likely Apple, who has been interested in the possibilities afforded by BMGs for some time, will invest heavily in commercializing the technology. Apple has a long history of pioneering cutting-edge manufacturing techniques, and its long-standing interest in design makes it likely to explore the material’s capabilities.
Sources
“Amorphous Metal Alloys Form Like Plastics”, Advanced Materials & Processes, January 2006, Jan Schroers and Neil Paton
“Thermoplastic blow molding of metals”, Materials Today, Jan-Feb 2011, Volume 14, Number 1-2, Jan Schroers, Thomas M. Hodge, Golden Kumar, Hari Raman, Anthony J. Barne, Quoc Pham, and Theodore A. Waniuk.Yale University.
“Stronger than steel, novel metals are as moldable as plastic.” ScienceDaily, 8 Feb, 2011. Web.
“The Superplastic Forming of Bulk Metallic Glasses”, Journal of Metals, 2005, 57, 35-39, Jan Schroers Read more

When Did You Last Change Your Oil?

It’s no secret that hydraulic fluid contamination leads to increased wear and corrosion, and decreased fluid life and system performance. At the same time, you want to maximize the life of your oil to reduce costs and downtime. It’s a balancing act.

Here are some tips for getting the most out of your hydraulic fluid:

• Don’t skimp on quality. Use a good quality hydraulic fluid from a reputable manufacturer following the specification recommendations from the pump and system manufacturer.
• Keep hydraulic fluid clean, cool, and dry. Maintain filtration and use clean lines to transfer hydraulic fluids into your equipment.
• Proactively analyze both your used fluid and your in-service fluid for contamination, oxidation, and to assess wear on the system.

Increasing the frequency of fluid changes may prove to be particularly cost effective in the long term. Research by the British Hydromechanics Research Association (BHRA) and National Engineering Laboratory indicated potential life extension factors of 10 - 50 times were possible on a variety of hydraulic equipment depending on oil contamination level. Read more

Q. Our testing lab is moving to a new building. Do our testing systems require recalibration after the move?

We strongly recommended that you recalibrate your systems after a move. In fact, many ASTM and ISO testing standards such as ASTM E4 and ISO 7500-1, have a mandatory requirement for recalibration.

If you have questions about this or you would like assistance with moving and recalibration of your system, please contact your local Instron service office. Additionally, we recommend taking into account other appropriate services at this time including preventive maintenance, system set up, and training. If you would like assistance with moving and recalibration of your system or if you have questions, please contact your local Instron service office. Read more

Syringe Testing is Painless!

Nobody really likes getting shots; however they have become less inconvenient for patients throughout the years thanks to the constant improvement of the design and materials used by syringe manufacturers.

Plastic disposable syringes were first introduced in 1961. The “disposable revolution” brought considerable benefits, the main one was the drastic reduction of infections transferred between patients since a syringe was only used once. In addition, the new disposable syringes optimized medical operations because the sterilization process for reusable glass syringes was no longer required.

One key factor in the shot process is how much force is required to operate the plunger of the syringe in both directions. This force level must allow the doctor or nurse to easily operate the syringe without causing harm to the patient.

Watch a video of a test (which meets ISO 7886-1 Annex G) that measures the required forces to operate the plunger of a disposable syringe.

Read more

Building Bridges at SAMPE

With more than 250 people in attendance and anticipation, we hosted the 3rd Annual Bridge Contest at the 20th SAMPE France Technical Meeting. This year we had 10 teams from 8 universities trying their hand at building a bridge strong enough to beat the other nine teams ....

We saw carbon fiber bridges constructed of special shapes (a fish belly), square bridges, and a very thin and flexible bridge which never broke. All teams did a great job constructing their bridges - it was impressive!

The winning bridge, designed with an arche shape, was from University Paul Sabatier, Toulouse with a strength of nearly 30 kN.

Next year, we'll need to supply a floor machine for the contest.

In addition to all those who participated in the contest, we like to give a special thanks to Mr Kauffmann and Magnin from SAMPE France.

Other pictures will be available soon on the Sampe France website - be sure to check them out! Read more

The Versatility of Milk Crates

About 24 months ago my car was vandalized and left resting on two milk crates ... why was it "resting" on the crates? Because my alloy wheels where missing. As much as I was shocked that someone would steal my wheels, I was more amazed that milk crates had the strength to hold up my Honda Civic ... and it got me thinking, "how much force can a milk crate take before failing?"

So we put the crates to the test - watch the video!

Read more

Instron Named Supplier of the Year

To find our place in the UK Plastics Testing Industry, we attended Interplas, where we met many customers and potential customers. This allowed our Application Experts the opportunity to understand and learn more about the market. During Interplas, we were entered into the European Plastics Product Manufacturer (EPPM) Supplier of the Year Awards; a contest where an independent research company contacted readers of EPPM and ask who is their preferred supplier. Based on 11 different categories, as well as overall brand image in 2011, Instron came out on top, winning Testing & Inspection Machinery Supplier of the Year.

It's not every day a Materials Testing Manufacturer is voted "Supplier of the Year" ..... so, we'd like to take this time to thank the readers of EPPM and everyone who made this a reality for Instron! Read more