Finite Element Method for Ship Composite-Based on Aluminum

*Prantasi Harmi Tjahjanti and Septia Hardy Sujiatanti*

### **Abstract**

The structure and construction of ships made of aluminum alloy, generally of the type of wrought aluminum alloy, when experiencing fatigue failure caused by cracking of the ship structure, is a serious problem. Judging from the 'weaknesses' of aluminum material for ships, this chapter will explain the use of alternative materials for ship building, namely aluminum-based composite material which is an aluminum alloy AlSi10Mg (b) ship building material based on the European Nation (EN) Aluminum Casting (AC) - 43,100, with silicon carbide (SiC) reinforcement which has been treated with an optimum composition of 15%, so that the composite material is written with EN AC-43100 (AlSi10Mg (b) + SiC \* / 15p. Composite ship model using ANSYS (ANalysis SYStem) software to determine the distribution of stress. The overall result of the voltage distribution has a value that does not exceed the allowable stress (sigma 0.2) and has a factor of safety above the minimum allowable limit, so it is safe to use. The reduction in plate thickness on the EN AC-43100 (AlSi10Mg (b)) + SiC \* /15p composite vessel is significant enough to reduce the ship's weight, so it will increase the speed of the ship.

**Keywords:** ship composite based on aluminum, EN AC-43100 (AlSi10Mg (b) + SiC\*/15p, software ANSYS, stress distribution

#### **1. Introduction**

The choice of material for ship building is carried out with several considerations, including physical properties, mechanical properties, material prices, and labor skills needed for the production process. Based on the material used to build ships, in fact it can be divided into two major parts, namely (a) steel ships and (b) non-steel ships. Non-steel ship materials include aluminum alloys which have been developing for more than 30 years and have replaced steel, namely in the use of commercial ships and on surface warships, especially for the deck and superstructure [1]. Even in Indonesia, on 18 December 2008, the Indonesian Navy (AL) launched its first warship (KRI), named KRI Krait-827 made of aluminum, with a speed of 25 knots. This warship is lighter than ships made of iron/steel (Jawa Pos, Desember 2008). The purpose of using aluminum/aluminum alloy is due to the density and modulus of aluminum 1/3 of the steel, thus significantly reducing the overall weight of the ship. The use of aluminum has become an alternative material used as a hull material in ship construction. Almost all of them use wrought aluminum with aluminum of marine grade: main alloy part magnesium (Mg) (alloys of marine grade), marine grade aluminum 5052 (used only for above water), marine

grade a luminum 5083 (used for underwater hulls), marine grade aluminum 5086, and marine grade structure of aluminum 6061.

However, the structure of a ship made of aluminum alloy, if it experiences fatigue failure caused by cracks in the ship's structure, it is a serious problem. Cracking itself is usually caused by a combination of rotational stress (torque) and stress concentration interacting with areas of the weak material [2]. The rate of structural cracking in aluminum is 30 times faster than the crack rate in steel when tested at the same stress with the same crack size [3]. On the other hand, the wear resistance on aluminum is also low [4], because aluminum is classified as a "soft" material compared to other metals.

To 'fix' the aluminum material into a strong and hard material, namely adding/ mixing it with a reinforcing material, which is a research to get a new material, called Composite Material is grouped in Metal Matrix Composite (MMC) [5–7]. If the method of mixing between the matrix and the reinforcement uses the casting method, it is called Metal Matrix Cast Composite (MMCC). Furthermore, if the metal used is aluminum-based, it is called Aluminum Metal Matrix Cast Composite (AMMCC).

Centered on the 'weaknesses' of ship aluminum sheet, this chapter offers an alternative sheet for shipbuilding, namely silicon carbide (SiC) reinforcement composite material based on aluminum. This aluminum alloy is made by casting aluminum alloy. Aluminum casting (AC) alloy is written: AlSi10Mg (b) in accordance with DIN EN (European Nation) 1706 expressed in chemical symbols written as EN AC-AlSi10Mg (b) and expressed in numeric, written EN AC-43100, so that the writing is combined to become EN AC-43100 (AlSi10Mg (b)). Reinforcement is SiC which has been treated with an optimum composition of 15% (written SiC\*), so that the composite material is written with EN AC-43100 (AlSi10Mg (b) + SiC\*/15p.

From the background above, this chapter will explain about making a numerical model of ships from the composite material EN AC-43100 (AlSi10Mg (b) + SiC \*/ 15p with the help of ANSYS ver.12.0 software to find out how the stresses are distributed. Wave input given is still water and dynamic waves (induced wave), not wave spectrum. Can be applied therein. From the results, it will be known which part of the ship building, the composite material AlSi10Mg (b) + SiC \*/15p can be applied therein.

#### **2. Ship composite base on aluminum**

#### **2.1 Aluminum alloy EN AC-43100 (AlSi10Mg(b)) as matrix**

EN AC43100 (AlSi10Mg(b)) alloy is an alloy of silicon aluminum which cannot be heat treated. It has strong flowability in a liquid state and almost no cracks occur in the freezing process [8]. This alloy is commonly used in the welding of aluminum alloys, both cast and wrought alloys as a welding medium or metal [Bergsma & Kassner, 1996]. The physical and mechanical properties of AlSi10Mg (b) can be seen in **Table 1**.

While the mechanical properties of aluminum casting EN AC-43100 (AlSi10Mg (b)) are summarized in **Table 2**.

#### **2.2 Silicon carbide (SiC) ceramic particles as reinforcement**

Silicon Carbide is a chemical compound composed of carbon and silicon alone. Created by electrochemical sand and carbon reactions at high temperature s. Silicon carbide has excellent abrasive properties, and has been developed and


#### **Table 1.**

*Physical and mechanical properties of aluminum AlSi10Mg (b) (casting material).*

manufactured for over a hundred years into grinding wheels and other abrasive goods. High power, low heat expansion, high thermal conductivity, high hardnes, high elasticity modulus, excellent heat shock resistance and superior chemical inertness are the general properties of silicon carbide.In a crystal lattice, silicon carbide with a tetrahedral chemical structure of carbon and silicon atoms has a strong bond which results in a very hard and strong material. Silicon carbide prevents acids or alkaline salts to strike. In air, SiC forms a protective layer of silicon oxide at 1200° C, which can be used up to 1600°C. The high thermal conductivity combined with low thermal expansion and high strength gives this material exceptional resistance to heat shock.

Nowadays, silicon carbide has grown into a high technological quality ceramic with outstanding mechanical properties. Applications are commonly used in abrasive materials, refractories, electrical conductors and have resistance heating, ignition, and electronic component applications. The engineering properties of silicone carbide are shown in **Table 3**.

In fact, numerical modeling of wrought aluminum vessels has never been possible. It existed until recently, because small ships are already set and included. So it is necessary to decide if the material can be used for shipbuilding. Ship composite EN ACAlSi10Mg(b) + SiC\*/15p must be numerically rendered Ship Modeling. Analysis of numerical computation using ANSYS software version 12.00 for seeing the stress distribution that occurs does not surpass the stress permits (0.2 sigma with that obtained from the tensile test), and also if it is safe for factor protection. The provided wave input is still induced by water and wave (the quasi-static one).

#### **3. Numerical modeling ship**

#### **3.1 Type and sizes ship**

Type of composite boats (EN AC-AlSi10Mg (b) + SiC\*/15p) to be modeled numerically using software ANSYS version 12.0 is Fast Patrol Boats with length over all (LOA) is 42.0 meters. Ship size is as follows:


**Table 2.** *Mechanical*

 *properties of aluminum*

 *casting.*

#### *Finite Element Methods and Their Applications*

## *Finite Element Method for Ship Composite-Based on Aluminum DOI: http://dx.doi.org/10.5772/intechopen.94973*


#### **Table 3.**

*Technical properties of silicon carbide.*


Shape hull of Fast Patrol Boat is known as V shaped hull, especially on the front (**Figure 1**). Planning regulations adapted to use the class from the Bureau Classification Indonesia (BKI) [10].
