#materials failure

Study compares physics and AI approaches for crack detection in powder compaction

Researchers at the Free University of Bozen-Bolzano, Italy, have compared physics-based simulation with machine learning (ML) for detecting cracks during powder compaction, concluding that the two approaches are best viewed as complementary tools rather than competing technologies. Crack formation during compaction remains a challenge in Powder Metallurgy, the authors explain, with defects compromising the mechanical integrity of sintered components. Finite element modelling can predict where cracks are likely to occur by analysing stress development within the compact, but the simulations are too computationally intensive for routine production monitoring. Machine learning, meanwhile, can analyse press sensor data in near real time, although its predictions are often criticised for lacking a clear physical explanation.

Creep

Also known sometimes as cold flow, creep is the slow plastic, or permanent, deformation of solid materials that occurs over time when said materials are subjected to constant stress. Creep is most significant in solid materials that are operated at high temperatures, such as jet engine turbines, as the rate to failure is typically faster the higher the temperature. Several internal mechanisms contribute to creep, dependent on materials' microstructures, properties, composition, etc., including dislocation movement, grain boundary sliding, and diffusion. Creep is not just limited to polycrystalline metallic solids; plastic, wood, concrete, and glass materials, among others, also experience creep.

Fouling

Fouling can be defined as "the settlement, and sometimes the growth, of undesired materials on solid surfaces in a way that reduces the efficiency of the affected part." Though it rarely leads to catastrophic failure of materials, fouling nevertheless impacts a part's function, leading to a failure of its intended purpose. Like corrosion, fouling has considerable economic impact. There are numerous types of fouling, including biofouling (accumulation of living organisms), precipitation fouling (accumulation of crystals precipitating from solution), and particulate fouling (accumulation of particulates), among others.

Though similar, with overlap in their definitions, fouling and corrosion are not necessarily the same thing. (Though corrosion fouling is one type of fouling where the corrosion deposits build up, and fouling corrosion is another thing entirely, where corrosion is caused by fouling.) Corrosion is caused in-situ, as a result of reactions with the material/part. Fouling is caused by build up of ex-situ material, i.e., material that is not a component of the part that is being fouled.

The effect of fouling on heat exchanges is of particular interest to the industries involved, as is membrane fouling.

Environmental Stress Cracking

One of the most common causes of brittle failure in thermoplastics is known as environmental stress cracking (beyond thermoplastics, it is more common in amorphous plastics than crystalline or semi-crystalline plastics). Environmental stress cracking refers to the fact that the failure is caused by both chemical exposure (the environment the plastic is exposed to) and stress - it is not the same as chemical attack and requires both components. This type of failure is also often referred to as an 'unexpected' failure, because the failure of a part can occur long after the chemical exposure that led to the issue. As such, testing for resistance to environmental stress cracking can take months.

Atomic-level engineering enables new alloys that won't break in extreme cold

Navigating the extreme cold of deep space or handling super-chilled liquid fuels here on Earth requires materials that won't break. Most metals become brittle and fracture at such low temperatures. However, new research is pioneering an approach to build metal structures atom by atom to create tough and durable alloys that can withstand such harsh environments. Traditional strengthening approaches are often not good enough for these applications. For example, a common heat treatment technique called precipitation hardening strengthens metals by creating tiny hard particles within their structure. But in extreme temperatures, the materials can lose their ductility (the ability to bend, stretch or be pulled into a new shape without breaking) and fracture suddenly.

Improved rubber processing makes material ten times stronger and resistant to cracking

Throughout its nearly 100-year manufacturing history, the crack resistance of natural rubber—one of the world's most widely used biomaterials—hasn't improved much. Until now. Materials researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have devised a way to produce natural rubber that retains its key properties of stretchiness and durability while greatly improving its ability to resist cracking, even after repeated cycles of use. The work is published in Nature Sustainability and is led by Zhigang Suo, the Allen E. and Marilyn M. Puckett Professor of Mechanics and Materials at SEAS. "Improving crack resistance will extend the material's service lifetime and therefore improve its sustainability," said first author and former SEAS postdoctoral researcher Guodong Nian.

Constance Tipper (16 February 1894 – 14 December 1995)

An English metallurgist, Constance Tipper (born Constance Fligg Elam) studied engineering at Newnham College in Cambridge in 1912. She would go on to hold a number of positions at various laboratories in the UK. By 1949 she had gained a position at Cambridge University, becoming the only full-time female faculty member in engineering. Tipper's research focus was primarily on the strength of metals and she is most well known for her work establishing existence of the ductile to brittle transition temperature in steels in the 1940s. The Tipper test is still used today to determine the brittleness of steels. She is also noted as the first person to study metal fracture surfaces using scanning electron microscopy.

Fracture Toughness

The fracture toughness of a material is typically defined as the critical stress intensity, above which cracks in a material will grow and lead to failure. This definition relies on preexisting cracks or flaws in a material, however while these flaws can be the initial stages of a crack they can also be pores in a material, inclusions, weld defects, etc. Fracture toughness for a given material is usually given as a range, as it can depend on environmental conditions as well as the respective stress and flaw orientations and the size/thickness of the part.