Advancements in Forensic Engineering Techniques
Forensic engineering of today gives a lot of emphasis on finding out the cause of malfunction of consumer items. The reason for this is businesses are being increasingly sued about allegedly faulty products. Also an ongoing need is felt of investigating explosions, fires, and rail and air crashes and other major accidents or potential crimes. The techniques used by forensic engineering in the past and in the present don’t differ a lot with each other. However, there is a definite improvement and accuracy in these techniques regarding coming to a conclusion. Knowing about these various techniques is quite interesting.
Techniques Used in the Past
The main techniques used previously by forensic engineering included:
- Analysis of the material used in terms of its microstructure
- Verification of associated temperatures
- Review of weights carried
- Analysis of the performance of the component
- Appraisal of witness evidence
These were normally done using x-ray diffraction, optical microscopy and chemical analysis.
Techniques Used Today
The techniques used in the past are required to be used even today. However they have become easier because of the introduction of more number of important concepts and techniques. Let’s see what they are.
Fracture mechanics is the study of loads applied to the components that contain cracks. It began in the 1920s with the concepts of Griffith on the fracture of easily breakable solids like glass, where he proposed that the strength of fracture was inversely proportional to the square root of largest crack’s length. Afterwards in the 1950s when fracture was seen in metals with no previous plastic (permanent) deformation, the fracture mechanics concepts were developed.
These concepts can be express as:
KIc = QÛfv (_a)
where KIc is fracture sturdiness, a task of the material
a is crack length
Q is a geometrical factor, associated to crack and component geometry
By analyzing the size of the crack, which has caused failure, and material, the stress that has brought about the failure can be measured and compared to the expected design stresses. By using fracture mechanics as factor of the design process, particularly in high integrity constructions and high power materials like oilrigs and aircrafts, it is rare to get instant quick fracture.
More often cracks develop by fatigue (recurrent stresses) or stress-corrosion (synergy between corrodant and tension-associated stress). This growth of crack is a function of intensity of stress (KI = QÛv (_a), where Û = stress).
Scanning Electron Microscope
SEM - Scanning Electron Microscopes
The surface of fractures can be examined at magnifications of thousands to find out modes of failure, and also the chemical structure of key factors of the microstructure. Commercial electron microscopes used for scanning were brought into use in the mid-60s. Their major benefit over traditional optical microscopy includes a greater magnification to 40-50000 from the optical microscope’s 1-2000 and a greater depth of focus by a factor of around 300. It enables to take a glance at fracture surfaces, which will be too coarse for proper optical examination and to examine polished parts at magnification of over 1000.
Scanning electron microscope works by casting an electron beam on a specimen, the focusing point being scanned line by line across the entire specimen. The back-scattered electrons, secondary electrons and emitted x-rays can build up images. Within the last decade, a more sophisticated kind of SEM has been made available which is called Environmental Scanning Electron Microscope (ESEM). Non-metal samples don’t require a conducting layer and may be inspected up to atmospheric pressures, creating great chances in both forensic engineering and sciences.
Secondary electrons will create an image of the object’s shape and so, will be used on surfaces of the fractures and on etched and polished sections. Back-scattered electron contrast is a function of atomic number, while the x-rays used for detecting the elements occurring the sample (EDAX analysis).
Finite Element Analysis
Finite element analysis involves determining temperatures at all locations and stresses within a body by numerical mathematics rather than analytical explanation of basic shapes. It depends on the segregating a body into separate elements that may be squares, triangles or other shapes, and studying the response of the body as one because the sum of the response is same as that of each component of the body.
Each part is typified by the value of an entity (displacement, stress) at the nodes (corners) of the part and values at locations in between were evaluated by interpolation. The technique was found out in the 50s for structural engineering problems, particularly in the aeronautical industry.
The term “finite element” was first used in 1960 and in the late 60s there was a generalization of the technique to solve problems in all other areas except structural engineering, like heat transfer.
Finite Element Analysis
Because calculations were numerical and elements were usually small in comparison to the size of structures or components, the usage of finite element technique was a bit limited till powerful yet cheap computing facilities (software and hardware) came into existence. In the beginning, problems solved with this technique were mono-dimensional but the advancement of the technique, particularly with greater computing power available, has been pulled out to 2 and 3 dimensions.
Computational Fluid Dynamics
Computational fluid dynamics makes use of numerical mathematics to find out effects of fluid (solids or gases) on structures or components. It also depends on a structure or component into a group of control volumes. For each of the groups, equations will be determined to describe the fluid (gas or liquid) flow. The increase in fire or a turbine blade’s cooling with compressor air can be modeled.
The technique became popular in the 1960s previously in the big aerospace companies.
With the reduction in the costs of computer software and hardware, the use of computational fluid dynamics has been greatly increased in the last decade. This has lessened the requirement of some wind tunnel testing and sped up the creation of solutions to design problems including fluid flow.
Computational Fluid Dynamics
Impact dynamics includes the use of analytical and numerical models and codes to determine the structure’s behavior when struck by rapidly-moving projectiles. The models of impact events have been taken to be important actually because experimental work in these fields can be hard, pricy and in some situations, illegal. For example, penetration of the skin of an aircraft by a portion of a missile, the passing of a shock wave from a blowing explosive or projection of a non-piercing projectile near a fuel tank.
In this field, computational techniques have become extremely important. Over the last 15 years, these techniques have left the nuclear and defense laboratories, particularly as sophistication in computational perspectives to finite element analysis as well as computational fluid dynamics have made the execution of models to dynamic procedures feasible.
The key to success of forensic engineering companies can be maintaining highly qualified and specialized experts in the field and a varied workload. Analyzing of patented engineering items is a very special branch of forensic engineering which investigates cases where one company has breached the patent of another. In such cases, which are complex and intricate, and also expensive to both the parties, forensic engineering can find out easy and inexpensive solution so that the case can be solved soon. So, forensic engineering can be a profession that will need most of its members to work part-time. These will include chartered engineers, several having post-graduate degrees in a specialty subject and more senior members may be Fellows of the concerned engineering or scientific institutions.